Applied Surface Science (v.216, #1-4)

Author Index (I-VIII).

Subject Index (IX-XXXII).

Preface by Akio Hiraki (1).

The National Si-Soft Project by Chun-Yen Chang; Charles V. Trappey (2-7).
Taiwan’s electronics industry emerged in the 1960s with the creation of a small but well planned integrated circuit (IC) packaging industry. This industry investment led to bolder investments in research, laboratories, and the island’s first semiconductor foundries in the 1980s. Following the success of the emerging IC manufacturers and design houses, hundreds of service firms and related industries (software, legal services, substrate, chemical, and test firms among others) opened for business and completed Taiwan’s IC manufacturing supply chain. The challenge for Taiwan’s electronics industry is to take the lead in the design, manufacture, and marketing of name brand electronic products. This paper introduces the Si-Soft (silicon software) Project, a national initiative that builds on Taiwan’s achievements in manufacturing (referred to as Si-Hard or silicon hardware) to launch a new wave of companies. These firms will contribute to the core underlying technology (intellectual property) used in the creation of electronic products.
Keywords: Si-Soft; Taiwan electronics industry; Electronics design;

The Si18O desorption yield was measured in the Si(0 0 1) surface temperature region from 900 to 1300 K at the 18 O 2 incident energies of 0.7, 2.2 and 3.3 eV by using supersonic 18 O 2 molecular beams. The real-time in situ O 1s photoemission spectroscopy was performed during surface chemical reactions of the O2 molecules with the Si(0 0 1) surface. The increase of SiO desorption yield with increasing incident energy shown in a temperature region higher than 1000 K implies that the angular distribution of SiO desorption changes toward the forward direction in addition to the incident energy-induced backbond oxidation. In turn, the desorption yield increased with decreasing incident energy in a temperature region from 900 to 1000 K. Oxygen uptake curves obtained by the real-time in situ O 1s photoemission spectroscopy revealed the coexistence of the passive and the active oxidation. The formation of the oxide-nucleus and their growth due to the enhanced O2 sticking by the action of incident energy suppress the SiO desorption.
Keywords: Oxidation; Photoemission spectroscopy; Si(0 0 1); Oxygen molecule; SiO; Synchrotron radiation;

Adsorption of Si atom on H-terminated Si(0 0 1)-2 × 1 surface by Tomihiro Hashizume; Hiroshi Kajiyama; Yuji Suwa; Seiji Heike; S. Matsuura; Jun Nara; Takahisa Ohno (15-18).
Adsorption and diffusion of Si atoms on a hydrogen-terminated Si(0 0 1)-2×1 surface is studied using scanning tunneling microscopy/spectroscopy and first-principles total-energy calculations. We find that the Si atoms randomly adsorb at the bridge site of Si dimers forming SiH2 clusters at room temperature, and move into the off-centred inter-bridge site after annealing at 250 °C.
Keywords: Silicon; Surface; Adsorption; Hydrogen termination; STM; First principles;

Temperature dependence of flat Ge/Si(0 0 1) heterostructures as observed by CAICISS by Ryo Tsushima; Mitsuhiro Katayama; Toshiaki Fujino; Masato Shindo; Tomohisa Okuno; Kenjiro Oura (19-23).
We have investigated temperature dependence of flat Ge/Si(0 0 1) heterostructures fabricated by hydrogen-surfactant mediated epitaxy, by means of coaxial impact-collision ion scattering spectroscopy (CAICISS). The transition temperature at the onset of surface roughening increases with the film thickness, which improves their thermal stability. Notably, for the thick films, the change in film morphology to a large island structure occurs in an almost first-order phase transition manner. These findings are consistent with our scanning electron microscopy (SEM) and atomic force microscopy (AFM) observations. The thickness dependence of the transition temperature can be correlated with strain relaxation at the surface of the initial film.
Keywords: Ge/Si(0 0 1) heteroepitaxy; Hydrogen surfactant; Film morphology; Thermal stability; Surface roughening; CAICISS;

Anomalously large band-bending for HF-treated p-Si surfaces by D. Watanabe; A. En; S. Nakamura; M. Suhara; T. Okumura (24-29).
Electronic properties of the HF-treated Si surfaces have been characterized by the Kelvin method combined with surface photovoltage (SPV) measurements. With the use of 340 nm ultraviolet light source, a relatively large SPV of −0.45 V was detected at a photocurrent density of 1 mA/cm2 for the diluted (e.g. 4.5%) HF-treated p-Si(0 0 1) surface. On the other hand, no SPV was induced for the HF-treated n-Si(0 0 1) wafer. This result indicates that there is anomalously large surface band-bending toward the surface, and Fermi-level position at the surface is pinned in the vicinity of the bottom of the conduction band at the HF-treated p-Si(1 0 0). It is considered that the residual fluorine responsible for an anomalously large band-bending at the p-Si(1 0 0) surface treated with HF. Furthermore, the value of the built-in potential for the HF-treated p-Si(0 0 1) surface was estimated to be about 0.60 eV at the room temperature from the result of the temperature dependence of the effective saturation current.
Keywords: Kelvin method; Surface photovoltage (SPV); H-terminated Si surface; Surface band-bending; Fermi level;

An offset of a straight step, called a kink, is occasionally formed on semiconductor surfaces. The motion of the kink on the Si(1 1 1) 7×7 surface in the [ 1 ̄ 1 ̄  2] step was studied in detail by high-temperature scanning tunneling microscopy (STM), and thermal fluctuations of the kink displacement along the step edges was observed. The kink displacement did not diverge with time, suggesting that a restoring force acts on the kink. The displacement, however, could be clearly represented by the gaussian distribution and it was therefore considered to be a Brownian particle. The temperature dependence of the mean square displacement of the kink position showed that the displacement is a thermal activation process with an apparent activation energy of 1.54±0.1 eV. From the equation of motion on the kink displacement including an incoming and outgoing flux as a fluctuation source, the phenomenological Langevin equation was derived. The activation energy of the kink displacement is related to the diffusion coefficient of the two-dimensional adatom gas and the latent heat of the atoms from the kink site to the surface adatom.
Keywords: Si(1 1 1); Atomic step; Kink; Surface diffusion;

Study of Sb adsorption on the Si(0 0 1)–In(4 × 3) surface by D Gruznev; Y Furukawa; M Mori; T Tambo; V.G Lifshits; C Tatsuyama (35-40).
The process of Sb adsorption onto Si(0 0 1)–In(4×3) surface phase has been studied using scanning tunneling microscopy (STM), reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES) techniques. Above 400 °C, Sb tends to destroy the initial In-induced phase and terminate the surface forming Sb/Si(0 0 1) interface. Between 400 and about 200 °C, however, the decomposition of In-induced reconstruction becomes partial; removing of In atoms from InSi bonds results in the relaxation of substrate atoms to the sequence of dimer rows separated by 4a 0 which is also destroyed by further Sb adsorption. Below 200 °C, the (4×1) structure remains intact against Sb deposition. In this case, In and Sb atoms form disordered layer mediated by the corrugation of (4×1) structure.
Keywords: STM; Si(0 0 1)–In(4 × 3); Sb adsorption; Partial decomposition;

We have investigated the surface stress evolution under nitridation process of silicon oxide by plasma exited nitrogen. The compressive surface stress, which had been formed by thin oxide on Si(1 0 0) were relaxed by the nitridation. During the nitridation, more than 40% of the initial compressive stress in 3 nm oxide was relaxed. We measured the stress evolution for plasma oxide films and thermal oxide films with thickness of 2–5 nm and found the same amount of the relaxation of oxide stress. Less than 3% of nitrogen was incorporated in SiO2, and not located at the SiO2/Si interface but uniformly distributed in the film with forming a N–Si2O bonding.
Keywords: Surface stress; Stress relaxation; Silicon oxide; Oxynitride; Plasma nitridation;

Novel post CMP cleaning using buffered HF solution and ozone water by Ching-Fa Yeh; Chih-Wen Hsiao; Wen-Shan Lee (46-53).
Post chemical mechanical polishing (CMP) cleaning is a key process for copper (Cu) CMP in dual damascene interconnection technology. During the post CMP cleaning, it is an important issue to minimize organic and Cu contamination residues on the dielectric surface. This study proposed a novel post CMP cleaning using HAL buffer hydrofluoric (BHF) solution and ozone (O3) water cleaning. The performance of the proposed cleaning technology was investigated and compared to conventional citric solution cleaning, which is currently used in post Cu CMP cleaning. From roughness, contamination residues and electrical characteristics, the proposed cleaning technology showed better performance than citric solution cleaning did. This excellent cleaning performance is attributed to the surface etching and contamination elimination effect of HAL BHF solution and O3 water. Based on the experimental results, the proposed cleaning technology is feasible and superior to the conventional post CMP cleaning.
Keywords: BTA; Buffered HF; Cu; Ozone water; Post CMP cleaning;

We have studied 6H-SiC(0 0 0 1)Si surfaces with and without Ni atoms on top. 6H-SiC(0 0 0 1) clean surfaces were obtained by resistive heating of a SiC sample for a few minutes at about 1100 °C in UHV. Structural change of such clean 6H-SiC(0 0 0 1) surface was studied by scanning tunneling microscope (STM) after heat treatment at several temperatures. Then we deposited 1–2 Å of Ni on thus cleaned surface. The initial stage of the adsorption process of Ni atoms on 6H-SiC(0 0 0 1) substrate was analyzed using STM to clarify Ni islands formation. Furthermore, we heated Ni(1–2 Å)/6H-SiC(0 0 0 1)Si specimens at 400–800 °C. After heating at 600 °C, 2√3×2√3 surface structure was observed. Structure model of this surface has been proposed.
Keywords: Low index single crystal surfaces; SiC; Ni/SiC; Nano-structures; Reconstruction; Scanning tunneling microscopy;

Hydrogen-related structural changes on CVD diamond (1 0 0) surfaces by ultra-high-vacuum annealing by J. Nakamura; S. Fukumoto; T. Teraji; H. Murakami; T. Ito (59-64).
Using an ultra-high-vacuum (UHV) scanning tunneling microscope (STM), we have investigated surface atomic structures of single-crystalline (1 0 0) diamond homoepitaxially grown by means of a microwave-plasma (MWP) chemical-vapor-deposition (CVD) method. STM images taken from B-doped (p-type) as-grown (H-terminated) diamond samples showed partially amorphous-like structures and partially unclear features related to (2×1)/(1×2) structures characteristic of H-terminated diamond (1 0 0). While the latter structures became clearer with increasing periods and temperatures of UHV annealing treatments well below 500 °C, substantially clear (2×1)/(1×2) structure images were obtained only after a sufficient annealing above 500 °C. A moderate UHV annealing at 150–200 °C sometimes resulted in the presence of disordered short-range (3×1) structures featured by row separations of 0.35 and 0.40 nm in very limited areas beside the (2×1)/(1×2) structures. These observations suggest the existence of both CH and CH2 bonds at the topmost surfaces, substantially small but possible changes in surface fractions of the CH and CH2 species during the UHV annealing and the final surface occupation of the CH bonds. In addition, STM images differently featured for both occupied and unoccupied states of the (2×1) structure are discussed in relation to bonding and anti-bonding states of the surface CH bonds.
Keywords: CVD diamond; Surface structure; STM; UHV annealing; Hydrogen;

Laterally microstructured devices suitable for applying high electric fields above ≈106  V/cm have been fabricated on homoepitaxially grown chemical vapor deposited (CVD) diamond thin layers using a focused ion beam (FIB) technique with 30 keV Ga ions. Characteristic regions of the microstructure fabricated on the undoped diamond were found to clearly change only after a high electric field ≥1×106  V/cm was applied to a non-implanted narrow volume. An energy-dispersive X-ray (EDX) analysis confirmed that substantial Ga accumulations occurred mainly in the positively-biased region to which ≈1018 Ga ions/cm2 were implanted to form graphitized (conducting) layers. A similar phenomenon was also observed in the graphitized region adjacent to the positively-biased side of the parallel thin graphitized layers both of which sandwiched the field-applied volume. This phenomenon clearly verifies that implanted Ga ions can easily diffuse in the graphitized layer having substantial amounts of lattice defects under the presence of hot carriers created in such high electric fields. The present FIB fabrication process combined with a newly developed Ga removing process demonstrates the possibility for realization of high electric field-compatible diamond devices with graphitized (metallic) areas to a submicron accuracy.
Keywords: Diamond thin film; Microstructure; Focused ion beam; Gallium implantation; High electric field;

Effect of Ni–Cu substrates on phase selection of hexagonal and cubic boron nitride thin films by Shigeo Kotake; Takaya Hasegawa; Kazutaka Kamiya; Yasuyuki Suzuki; Takami Masui; Yoshihiro Kangawa; Kohji Nakamura; Tomonori Ito (72-77).
In this study, the dependence of the phase selection of BN on the lattice parameter and the crystal structure of the substrate was clarified. BN thin film was prepared by reaction RF sputtering method on polycrystalline Ni–Cu complete solid solution alloy. Using empirical potentials, the polytypes of BN thin films were systematically investigated by considering lattice constraint due to various interface atomic arrangements and orientations such as c-BN or h-BN on cubic (0 0 1) or (1 1 1) substrates. From IR spectrum, merely c-BN phase was observed from the specimen on Cu and Ni0.8–Cu0.2 alloy. Moreover, the empirical potential calculations reveal that c-BN thin films on (0 0 1) substrates can be stabilized in the substrate lattice parameter of 3.2<a<4.4  A ̊ including Cu and Ni at both thin film and interface regions. From these experimental and calculated results, the strain energy at the semiconductor–metal interface proved to be dominant factor for the phase selection of BN thin films.
Keywords: Cubic and hexagonal boron nitride; Reaction RF sputtering; Lattice mismatch; Metal–semiconductor interfaces; Nickel and copper alloy;

Anisotropy of lateral growth rate in liquid phase epitaxy of {0 0 1} InP by Toshio Kochiya; Yutaka Oyama; Ken Suto; Jun-Ichi Nishizawa (78-82).
The angular dependences of the lateral growth rate are determined as the functions of growth temperature and growth time in liquid phase epitaxy of (0 0 1) InP at low growth temperature of 330–450 °C. From the deformation of artificially made tables after epitaxy, it is shown that the lateral growth rate has a strong anisotropy in [1 1 0] direction especially at low growth temperature (T g<400 °C). This indicated that kink density was high in [1 1 0] direction on InP(0 0 1) surface. It is also shown that the anisotropy of lateral growth rate decreases as the growth temperature becomes high.
Keywords: InP; LPE; Crystal morphology; Surface and interface phenomena; Surface migration; Anisotropy;

Lattice distortion near InGaP compound semiconductor surface due to surface treatment of bias sputtering by T. Emoto; Y. Yoshida; K. Akimoto; A. Ichimiya; S. Kikuchi; K. Itagaki; H. Namita (83-87).
Strain fields near InGaP surfaces due to bias sputtering are affected by the bias voltage used in this surface-cleaning treatment. Measured rocking curves of an InGaP113 reflection under grazing X-ray incidence conditions consisted of a main peak and broad sub peaks. The shape of the broad sub peaks was due to a compositional fluctuation near the subsurface. Changes in the main peak versus bias voltage curves indicate that bias sputtering introduces a tensile strain to the InGaP surface. Furthermore, changes in the sub peak versus supplied bias voltage curves indicate that excessive sputtering generates a heavy compositional fluctuation near the InGaP subsurface. In conclusion, based on the measured strain and compositional fluctuation, a heavy compositional fluctuation generally causes a large tensile strain near the InGaP surface.
Keywords: III–V semiconductor; Synchrotron radiation analysis; Strain; Sputtering; Oxide-semiconductor interface;

An influence of grain boundaries in cadmium mercury telluride (CMT) Cd x Hg1−x Te films with a cellular or polycrystalline structure on the processes of segregation of point defects and generation and recombination of carriers under laser irradiation is studied. It is established that the intergrain path of CMT films, acting as electrical active interface, can fulfill the function of sinks, recombination inclusions as well as create potential barriers for recombination of the charge carriers. The laser-stimulated photosensitization of CMT films with a cellular structure, a jump in current–illumination characteristics (CICs) and anomalous injection-level dependence of the nonequilibrium carrier lifetime in CMT polycrystalline films at high illumination intensities are analyzed.
Keywords: Cd x Hg1−x Te polycrystalline film; Laser irradiation; Grain boundary; Segregation; Photoconductivity; Potential barriers;

Passivation of defects in polycrystalline Cu2O thin films by hydrogen or cyanide treatment by S. Ishizuka; S. Kato; Y. Okamoto; T. Sakurai; K. Akimoto; N. Fujiwara; H. Kobayashi (94-97).
The effects of the passivation of defects in polycrystalline nitrogen-doped cuprous oxide (Cu2O) thin films with hydrogen or cyanide treatment were studied. In the photoluminescence (PL) measurements, although the emission was not observed before treatment, luminescence of Cu2O at around 680 nm was observed after each treatment. This improvement in the luminescence property may be due to the passivation of non-radiative recombination centers by H or CN. The hole carrier concentration increased from the order of 1016 to 1017  cm−3 with hydrogen or cyanide treatment. From these results, both the hydrogen and cyanide treatments were found to be very effective to passivate defects and improve the optical and electrical properties of polycrystalline Cu2O thin films. The thermal stability of the passivation effects by the cyanide treatment is, however, superior to that by the hydrogen treatment.
Keywords: Cuprous oxide; Sputtering; Hydrogen treatment; Cyanide treatment;

Modification of GaAs and copper surface by the formation of SiO2 aerogel film as an interlayer dielectric by Sung-Woo Park; Sang-Bae Jung; Min-Gu Kang; Hyung-Ho Park; Hae-Cheon Kim (98-105).
For the application of SiO2 aerogel film to GaAs based devices, the changes of interfacial chemical bonding state of HCl-cleaned (or S-passivated) GaAs surface were investigated using monochromatic X-ray photoelectron spectroscopy after immersing the GaAs in each constituent of SiO2 sol. A large amount of oxide was formed on the HCl-cleaned GaAs after the treatment using tetraethoxysilane and de-ionized water due to hydroxyl group in SiO2 sol, while the S-passivated GaAs was not oxidized. The interfacial surface of GaAs was also investigated after the removing SiO2 aerogel film formed by supercritical drying. The aerogel film showed 80% of porosity and low dielectric constant of 1.8. Normally the oxidation of GaAs was successfully suppressed with S-passivation, however during the supercritical drying due to the high temperature and pressure, S-passivation layer was completely decomposed, and GaAs-oxides and elemental As were generated somewhat, but less than the case of HCl-treated GaAs.Furthermore, the formation of SiO2 aerogel film on copper metal substrate was revealed to induce a modification of metal surface. The modified and oxidized state of copper surface formed during the formation of the aerogel film was found to be not greatly influenced on the leakage current behavior of SiO2 aerogel/Cu system.
Keywords: SiO2 aerogel; GaAs; Copper; Sulfur passivation; XPS;

Interface formation and properties of α-NPD thermally deposited on CVD diamond films by Min-Seung Chun; Tokuyuki Teraji; Toshimichi Ito (106-112).
We have investigated the interface formation between hydrogen- or oxygen-terminated homoepitaxial (1 0 0) chemical-vapor-deposited (CVD) diamond film and N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4″-diamine (α-NPD) using X-ray photoelectron spectroscopy (XPS) to confirm both possibilities of CVD diamond as hole transport layer and transparent anode electrode for α-NPD as a possible organic light-emitting diode (OLED) material. In the case of α-NPD deposited on the H-terminated diamond substrates, the peak positions of both C 1s and N 1s spectra shifted to their lower binding energy sides, clearly differing from those in case of α-NPD deposited on a Si substrate where no remarkable peak shift was observed. This suggests that some electrons were transferred from the H-terminated CVD diamond to the deposited α-NPD. In the case of O-terminated diamond, however, completely different variations were found for the measured XPS peaks. No thickness-dependent peak shift was observed while the relative energy position of the α-NPD C 1s to the diamond C 1s was higher by 1.7 eV. The possible origin of the interface interaction is discussed in relation to band bending effect, change in the surface dipole layer between the H- and O-terminated diamond and change in energy levels of the α-NPD molecular orbitals after the interface formation.
Keywords: XPS; CVD diamond; Interface; Band bending; α-NPD; OLED;

Contactless electrical characterization of surface and interface of SOI materials by S Nakamura; D Watanabe; A En; M Suhara; T Okumura (113-118).
Electronic properties of the surface as well as the interface of silicon-on-insulator (SOI) materials have been characterized by the Kelvin method combined with surface photovoltage (SPV) measurements. In order to separate the interface properties from the surface ones, we used the data for the bulk Si surface, which was treated in the same manner, i.e. dipping in a diluted HF solution, as for the SOI surface. From the temperature dependence of the SPV for the bulk Si, the values of the built-in potential, the surface state density and the surface recombination velocity were determined to be about 0.60 eV, 6×1011  cm−2 and 6×103  cm/s, respectively, for the HF-treated Si surface. By taking these values into account, we analyzed the SPV data for separation by implanted oxygen (SIMOX) wafer. The values of the interface state density and the interface recombination velocity at the buried-oxide/SIMOX interface were estimated to be about 3×1012  cm−2 and 3×104  cm/s, respectively.
Keywords: Kelvin method; Surface photovoltage; Silicon-on-insulator; Contactless IV method; Surface; Interface;

In previous studies, device-quality Si–SiO2 interfaces and dielectric bulk films (SiO2) were prepared using a two-step process; (i) remote plasma-assisted oxidation (RPAO) to form a superficially interfacial oxide (∼0.6 nm) and (ii) remote plasma enhanced chemical vapor deposition (RPECVD) to deposit the oxide film. The same approach has been applied to GaN–SiO2 system. Low-temperature (300 °C) remote N2/He plasma cleaning of the GaN surface, and the kinetics of GaN oxidation using RPAO process and subcutaneous oxidation during the SiO2 deposition using an RPECVD process have been investigated from analysis of on-line Auger electron spectroscopy (AES) features associated N and O. Compared to single-step SiO2 deposition, significantly reduced defect state densities are obtained at the GaN–dielectric interfaces by independent control of GaN–GaO x (x∼1.5) interface formation by RPAO, and SiO2 deposition by RPECVD.
Keywords: GaN–dielectric interfaces; Surface leaning; Subcutaneous oxidation; Ga2O3; SiO2; MOSd devices;

Remote plasma-assisted nitridation or RPN is demonstrated to be a processing pathway for nitridation of Zr and Hf silicate alloys, and for Al2O3, as well. The dependence of nitrogen incorporation on the process pressure is qualitatively similar to what has been reported for the plasma-assisted nitridation of SiO2, the lower the process pressure the greater the nitrogen incorporation in the film. The increased incorporation of nitrogen has been correlated with the penetration of the plasma-glow into the process chamber, and the accompanying increase in the concentration of N2 + ions that participate in the reactions leading to bulk incorporation. The nitrogen incorporation as been studied by Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS) and X-ray absorption spectroscopy (XAS).
Keywords: Remote plasma nitridation; Auger electron spectroscopy; X-ray photoelectron spectroscopy; X-ray absorption spectroscopy; Zirconium and hafnium silicate alloys; Al2O3;

The phase transition from Langmuir-type adsorption to two-dimensional (2D) oxide island growth during initial oxidation on the Si(0 0 1) surface was investigated by real-time Auger electron spectroscopy (AES) combined with reflection high-energy electron diffraction (RHEED). Curve-fitting analysis of the oxygen uptake curve obtained by O-KLL Auger electron intensity revealed that the phase transition occurs steeply at ∼630 °C and no oxidation occurs after completion of 2D growth of oxide islands, whereas oxides grows gradually at the interface following Langmuir-type adsorption. It was observed that the very thin oxide layer grown at 616 °C is more easily decomposed than that grown at 653 °C in spite of almost the same thickness. Furthermore, the RHEED intensity ratio between half-order spots indicated that etching of the surface starts suddenly just at the phase transition temperature of ∼630 °C. The steepness of the phase transition, the sudden start of SiO desorption and the difference in the interfacial oxidation and decomposition between two oxidation schemes are comprehensively interpreted using a surface reaction model in which O2 adsorption on the Si(0 0 1) 2×1 surface changes drastically from barrier-less adsorption into dimer backbonds for Langmuir-type adsorption to formation of desorption precursor SiO in pairs with dimer vacancies for 2D oxide island growth, and coalescence of SiO leads to nucleation and 2D growth of oxide islands.
Keywords: Silicon; Oxidation; Auger electron spectroscopy; Reflection high-energy electron diffraction (RHEED); Surface chemical reaction; Real-time monitoring;

Theoretical study on the initial processes of nitridation of silicon thin film by Seiichi Yoshida; Kentaro Doi; Koichi Nakamura; Akitomo Tachibana (141-148).
The initial processes of nitridation of silicon thin film have been examined by means of the first-principle calculations. The nitrogen atom on the bare silicon(1 0 0) surface stays around the surface due to the dangling bond of the first-layer silicon, and the large stabilization on the bare silicon surface raises the energy barrier of the penetration of the nitrogen atom into the surface. The nitrogen atom on the H-terminated silicon surface can penetrate into the surface by crossing over the small energy barrier. In the nitridation by using nitrous oxide (N2O) molecule, N2O can be adsorbed only with the large NN bond length, and then an exothermic elimination of nitric oxide (NO) molecule from the adsorbed nitrogen atom on the bare silicon surface takes place. The electronic processes have been discussed in terms of the quantum mechanical energy densities, which give new images of microscopic electronic stresses in the interaction system.
Keywords: Formation of SiON film; Hydrogen termination; Nitridation of silicon surface; First-principle calculation; Quantum mechanical energy density;

The growth and structural evolution of the carbon nitride (CN x ) film, deposited by rf magnetron sputtering in Ar/N2 discharge, were studied. The CN x (0.23≤x≤0.71) films were deposited on Si(1 0 0) at rf power between 50 and 250 W. Simultaneously, Ar/N2 gas ratio was varied from 0 to 18 with total pressure kept at 6.6×10−1  Pa. The composition, structure, and chemical bonding configuration of the CN x films were found to be strongly dependent on deposition parameters (rf power and Ar/N2 gas ratio). Based on these results, a relationship between deposition parameter and film properties ([N]/[C] ratio, surface roughness, and sp3/sp2 bond ratio) was established.
Keywords: Carbon nitride (CN x ); rf magnetron sputtering; Structural modification;

The role of vacuum ultraviolet in H2 plasma treatment on SiO2 aerogel film by Sang-Bae Jung; Hyung-Ho Park; Haecheon Kim (156-162).
SiO2 aerogel film has been drawn an attention as excellent dielectric material due to its ultra low dielectric constant. SiO2 aerogel film could exhibit the improved electrical property after plasma treatment due to the removal of organic group. However, the role of vacuum ultraviolet (VUV) was not investigated in spite of high energy of VUV radiated during plasma processing. In this work, the radiation effect of VUV on SiO2 aerogel film was investigated during H2 plasma treatment. H2 gas was selected from its lightest atomic mass and strong photon emission in the VUV region. LiF single crystal was used as a VUV filter to permit the transmittance of the VUV radiated from H2 plasma but not with chemical species and reactive ions. It was found that VUV radiation during H2 plasma treatment plays a role of removal of organic group and rearrangement of siloxane bond.
Keywords: Low-k; SiO2 aerogel film; Hydrogen; Plasma; LiF filter; Vacuum ultraviolet;

Deposited metal layers on single crystal silicon can react at low temperature in an oxidizing ambient to produce silicon oxide. Akio Hiraki carried out the pioneering work in the early 1970s at California Institute of Technology. In this study Au/Si is revisited and compared with the Ag/Si system. Under oxidizing ambient conditions where oxide layers are formed in the Au/Si, no detectable oxide layers are formed in the Ag/Si system. The Ag layers agglomerates into a discontinuous film.
Keywords: Silicon; Gold; Silver; Oxidation; Agglomeration; Electronegativity;

Surface and interface study of Cu (film)/SiC (substrate) system by Z. An; M. Hirai; M. Kusaka; M. Iwami (169-173).
We have investigated the diffusion, agglomeration, and reaction at Cu/3C–SiC interface, using soft X-ray emission spectroscopy (SXES) and photoemission electron microscopy (PEEM). By measuring Si Kβ emission, the diffusion and/or agglomeration of Cu atoms at Cu (60 nm)/3C–SiC interface were found to occur obviously after annealing at 350 °C and to be enhanced with increasing annealing temperature. PEEM observations for a Cu (30 nm)/3C–SiC sample indicated that the Cu film began agglomerating at 550 °C annealing from the edge of the Cu film on the 3C–SiC substrate. The agglomeration spread from the edge to the middle region of the Cu film with the increase of temperature. At 850 °C annealing, the Cu agglomeration was observed in the whole area of the Cu film. The formation of Cu3Si was found from SXES analysis for Cu/3C–SiC(0 0 1) specimens annealed at temperatures higher than ∼850 °C, which indicates the agglomerated material observed by PEEM at 850 °C is Cu3Si.
Keywords: Silicon carbide; Copper; Diffusion and agglomeration; Interface reaction; X-ray emission; Photoemission electron microscopy;

Effect of Al interlayers on two-step epitaxial growth of CoSi2 on Si(1 0 0) by Osamu Nakatsuka; Hiroyuki Onoda; Emi Okada; Hiroya Ikeda; Akira Sakai; Shigeaki Zaima; Yukio Yasuda (174-180).
We have performed the two-step epitaxial growth of CoSi2 on Si(1 0 0) surfaces with Al interlayers. Microstructures of the surface and the interface during the growth have been investigated by scanning tunneling microscopy and transmission electron microscopy (TEM). At the first-step growth, the introduction of an 1-monolayer (ML)-thick Al interlayer prior to a 3-ML-thick Co layer deposition on the Si clean surface results in the formation of two dimensional islands of epitaxial CoSi2 with higher coverage, compared to the case without the Al interlayer. Cross-sectional TEM observations revealed atomically-flat CoSi2–Si interfaces. At the second step, CoSi2 is epitaxially grown on these islands that acts as a template layer. In-depth growth of CoSi2 domains is also observed to occur forming {1 1 1} facets at the CoSi2–Si interfaces. Effects of the Al interlayer on the growth morphology of epitaxial CoSi2 are discussed.
Keywords: CoSi2; Interface; Epitaxy; STM; TEM; Two-step growth;

Diffusion barrier properties of nano-crystalline TiZrN films in Cu/Si contact systems by Mayumi B. Takeyama; Takaomi Itoi; Eiji Aoyagi; Atsushi Noya (181-186).
Ternary nitride TiZrN films with nano-crystalline grains of 2–10 nm in size and ∼90 μΩ cm in resistivity were successfully prepared as a material applicable to a thin diffusion barrier of low electrical resistivity. In the Cu/TiZrN/Si contact system, a TiZrN film with ∼10 nm thickness is the barrier adequate to suppress the extremely small quantity of Cu penetration into the Si substrate upon annealing at 600 °C for 1 h without significant structural change and solid-phase reaction. The observed stable nano-crystalline structure and chemically inert characteristic of TiZrN were the dominant features for the successful demonstration of high performance barrier properties of thin TiZrN films.
Keywords: Metallization; Contacts; Diffusion barriers; Nano-crystalline; TiZrN;

Nano-structure of transition-metal (Ti, Ni)/SiC system: photo-emission electron microscopy and soft X-ray fluorescence spectroscopy by Masaaki Hirai; Joselito P. Labis; Akihiko Ohi; Chihiro Kamezawa; Yuhji Morikawa; Kenichi Yoshida; Masahiko Kusaka; Motohiro Iwami (187-191).
We have studied nano-structure of transition-metal film (Ti, Ni)/SiC (substrate) contact systems by using a photo-emission electron microscopy (PEEM) and a soft X-ray fluorescence spectroscopy (SXFS). The PEEM and SXFS studies using light sources of a Hg lamp and a synchrotron radiation, respectively, have been applied to a nondestructive buried interface analyses and a surface nano-structure study for a thin-film (Ti, Ni)/substrate (3C–, 4H–SiC) contact system.A PEEM image after a heat-treatment of Ti (10 nm)/3C–SiC contact system at 800 °C has shown small clusters of 2–3 μm in diameter on a specimen surface. On the other hand, a PEEM image of Ni (4 nm)/3C–SiC contact system has shown uniform surface morphology with increasing annealing-temperature up to 650 °C. Therefore, Ti (ultra thin film)/SiC (substrate) system is expected to be a good candidate to form nano-structure on top, whereas Ni is suitable for uniform contact at elevated temperatures.In SXFS, we have studied in-depth structure through the electronic states from deep inside to near surface region by changing an angle of incident light against a sample surface. Valence band electronic structure in the top thin-film for Ti/4H–SiC contact system is considered to be a combination of Ti-silicide and -carbide and/or graphite from SXFS study. On the other hand, it is the case that Ni/4H–SiC contact system is composed of Ni-silicide with crystallized graphite due to a heat-treatment until 950 °C.
Keywords: SXFS; PEEM; Nano-structure; 3C–SiC; 4H–SiC; Transition-metal;

Properties of GaN and AlGaN Schottky contacts revealed from IVT and CVT measurements by T Sawada; Y Izumi; N Kimura; K Suzuki; K Imai; S.-W Kim; T Suzuki (192-197).
Interface properties of metal/GaN, AlGaN Schottky structures formed on oxide-etched and intentionally oxidized surfaces are studied by IVT and CVT measurements. The characteristics support the previously proposed “surface patch” model, where the patches with low Schottky barrier heights (SBHs) cause a leakage current. The true SBHs were obtained from high-temperature IV curves with S-values of 0.28 and 0.20 for n- and p-GaN samples, respectively. Thermally oxidized GaN surfaces represented a reduction of the effective SBH for Ni/n-GaN sample. IVT characteristics showed that the leakage current due to surface patches is comparable with that of the oxide-etched sample. The current drift was less than 0.1% within the range of 1–104  s. On the other hand, anodized GaN surface led to increase of the SBH up to 0.3 eV, owing to formation of a relatively thick oxide layer. The oxide-etched Au/n-Al0.2Ga0.8N sample on HEMT wafer represented a considerably reduced effective SBH at RT, because of a tunneling leakage current. However, the true SBH was deduced to be 1.4 eV from the IVT characteristics. The annealing in N2 flow was again effective to improve the interface properties.
Keywords: GaN; AlGaN; Schottky barrier height; Native oxides; IVT; CVT;

We have proposed a mechanism of nonideality in nearly ideal Au/n-Si Schottky barriers (SBs), which explains various experimental observations called the T o anomaly. Because of the nature of the metal-induced gap states (MIGS), positively ionized defects induced by the process very close to the interface are considered to cause local lowering of the Schottky barrier height (SBH) due to filling-up of the MIGS. The formulation of the defect density is revised to be consistent with the experimental observations. There is a potential drop of more than 100 mV at about 20 Å from the interface due to the space–charge of the defects. The saddle potential for the low-SBH spot is lowered by this potential drop. Therefore, the local SBH lowering is observable in the IV characteristics.
Keywords: Schottky barrier; Silicon; Inhomogeneity; Defect; Potential distribution;

Interface-controlled Gd2O3/GaAs system for ferroelectric memory application by Jun-Kyu Yang; Woo Sik Kim; Hyung-Ho Park (203-207).
The formation of Gd2O3/substrate-GaAs structure was accomplished by two-step electron-beam (e-beam) deposition including ultra-thin Gd-metal and successive Gd2O3 layers. The deposition was carried out on HCl-cleaned GaAs containing elemental As on it. The pre-deposition of Gd-metal removes elemental As state in GaAs surface and forms interfacial state free from GaAs-oxides. However, Gd-metal turns to be oxide during the deposition by absorbing oxygen from GaAs surface and atmosphere. The successive deposition of Gd2O3 was performed with in situ anneal of the substrate and this permitted preferential growth of Gd2O3 with oriental relationship with substrate GaAs as Gd2O3{1 1 1}〈1 1 0〉||GaAs{0 0 1}〈4 7 0〉 with less than 1.5% of lattice mismatching. Capacitance–voltage (CV) and current density–voltage (JV) measurements indicated that the interface was seriously degraded when the anneal temperature exceeded 600 °C. The feasibility of Gd2O3 film as a buffer layer for ferroelectric-gate/GaAs structure was proved.
Keywords: Gd inter-layer; GaAs; Lattice match; Preferred orientation;

Built-in interface in high-κ gate stacks by Masahiko Hiratani; Kazuyoshi Torii; Yasuhiro Shimamoto; Shin-Ichi Saito (208-214).
The advantage of using the Al2O3 gate dielectric is discussed from thermodynamic and kinetic standpoints. We fabricated n-field effect transistors with Al2O3 dielectrics and built-in interfacial SiO2 having thicknesses of 0.6–2.0 nm to investigate the effect on electron mobility and gate leakage current. The mobility was reduced and the shift in flat-band voltage was increased with decreases of the thickness of the interfacial SiO2. We propose that a fixed charge is generated at the interface of Al2O3/interfacial SiO2, it induced Coulomb scattering to the surface channel, and that the electron mobility is consequently reduced. The plot of gate leakage current against the total physical thickness, which includes Al2O3 and interfacial SiO2 dielectrics, showed the enhanced leakage current. This suggests that the band offset may be lowered at the interface of ultra-thin SiO2/Si beneath the Al2O3 dielectric.
Keywords: High-κ; Gate stack; Interface; Mobility; Fixed charge;

Band offset energies in zirconium silicate Si alloys by Gerald Lucovsky; Bruce Rayner; Yu Zhang; Gunther Appel; Jerry Whitten (215-222).
Transition metal silicates, (ZrO2) x (SiO2)1−x , with dielectric constants, k>10 have been proposed as alternative dielectrics for advanced Si devices. Studies by X-ray absorption, X-ray photoelectron and Auger electron spectroscopy are combined to identify the compositional variation of the valence and conduction band offset energies with respect to Si in Zr silicate alloys. The minimum conduction band offset energy, associated with localized Zr 4d-states, is ∼1.4 eV, and is independent of alloy composition, while valence band offsets decrease monotonically with increasing ZrO2 content. Differences between the coupling of tunneling electrons to localized Zr 4d and extended Si 3s states, characterized by respective tunneling masses of ∼0.5m o and ∼0.2m o, combine to contribute to a minimum in the direct tunneling current in the mid-silicate-alloy composition range, x∼0.4–0.6.
Keywords: Plasma processing and deposition; Auger electron spectroscopy; X-ray photoelectron spectroscopy; X-ray absorption spectroscopy; Zirconium silicate alloys; Semiconductor-dielectric band offset energies;

Diffusion and incorporation of Zr into thermally grown SiO2 on Si(1 0 0) by Masanori Yamaoka; Hideki Murakami; Seiichi Miyazaki (223-227).
We have studied the Zr diffusion into ultrathin thermally grown SiO2 on Si(1 0 0) from Zr-rich oxides at 750–1000 °C in N2 ambient with combination of photoemission measurements and wet-chemical SiO2-thinning in a dilute HF solution. The chemical bonding features incorporated Zr atoms into SiO2 and the influence of the Zr incorporation on the gap states have also been evaluated by analyzing X-ray photoelectron and total photoelectron yield spectra, respectively. The measured Zr depth profiles show that the Zr diffusion at 750 and 900 °C can be characterized as the cases under constant-surface-concentration conditions with the diffusion constants of ∼1×10−19  cm2/s at 750 °C and ∼1×10−18  cm2/s at 900 °C, while the diffusion at 1000 °C is likely to be the case under a constant-total-concentration condition. No increase in the gap states with Zr incorporation into SiO2 is confirmed by total photoelectron yield measurements.
Keywords: High-k gate dielectrics; Zr-silicate; Diffusion; X-ray photoelectron spectroscopy; Photoelectron yield spectroscopy; Defect state density;

Comparison of thermal and plasma oxidations for HfO2/Si interface by S. Hayashi; K. Yamamoto; Y. Harada; R. Mitsuhashi; K. Eriguchi; M. Kubota; M. Niwa (228-233).
The HfO2/Si interface stability has been investigated by using a rapid thermal annealing (RTA), an inductively coupled plasma (ICP) and a reactive sputtering, as a comparison of thermal and plasma oxidations of the Hf/Si interface. Reduction in both capacitance equivalent thickness (CET) and leakage current density (J g) was difficult to be attained by the thermal oxidation since it accompanies the crystalline HfO2 with SiO2-like interface. Advantage is found for the plasma oxidation technique to oxidize Hf metal at low temperatures remaining the HfO2 in an amorphous phase with silicate interface. Reduction in both CET and J g was attained by the plasma oxidation and a Hf metal pre-deposition technique.
Keywords: HfO2; Reactive sputtering; RTA; Plasma; Oxidation;

Chemical and electronic structures of Lu2O3/Si interfacial transition layer by H. Nohira; T. Shiraishi; T. Nakamura; K. Takahashi; M. Takeda; S. Ohmi; H. Iwai; T. Hattori (234-238).
The composition of transition layer (TL) formed between Lu2O3 and Si(1 0 0) substrate was determined non-destructively by applying newly developed depth profiling method to the angle-resolved Si 2p and Lu 4d photoelectron spectra. The conduction and valence band alignments of Lu2O3 with respect to Si(1 0 0) were also determined from the measurement of O 1s photoelectron spectra and valence band spectra.
Keywords: High-K; Lu2O3; Transition layer; Silicate; Depth profiling; XPS;

Oxygen radical treatment applied to ferroelectric thin films by Ichirou Takahashi; Hiroyuki Sakurai; Atsuhiko Yamada; Kiyoshi Funaiwa; Kentarou Hirai; Shinichi Urabe; Tetsuya Goto; Masaki Hirayama; Akinobu Teramoto; Shigetoshi Sugawa; Tadahiro Ohmi (239-245).
A low dielectric constant ferroelectric Sr2(Ta1−x ,Nb x )2O7 (STN) film formation technology which is applied to floating gate type ferroelectric random access memory (FFRAM) has been developed. The high ferroelectric performance of the STN capacitor has been achieved by plasma PVD and an oxygen radical treatment using microwave-excited (2.45 GHz) high-density (>1012  cm−3) low electron temperature (<1 eV) Kr/O2 plasma. Oxygen radical treatment can effectively oxidize ferroelectric film at 400 °C.
Keywords: Sr2(Ta1−x ,Nb x )2O7 (STN); Oxygen radical treatment; Low temperature treatment; Oxidizing ferroelectric effectively; Kr/O2 plasma;

Reliability of silicon nitride gate dielectrics grown at 400 °C formed by microwave-excited high-density plasma by Ichiro Ohshima; Weitao Cheng; Yasuhiro Ono; Masaaki Higuchi; Masaki Hirayama; Akinobu Teramoto; Shigetoshi Sugawa; Tadahiro Ohmi (246-251).
Silicon nitride gate dielectric metal-nitride–semiconductor (MNS) having a Si3N4 film grown at 400 °C by microwave-excited high-density plasma has been developed. We demonstrated the electric characteristics of the MNS capacitors with the Si3N4 film grown by microwave-excited high-density plasma using krypton (Kr) gas. The MNS capacitors have larger TDDB lifetime and have lower leakage current capability compared with the MOS capacitors. The TDDB lifetime of the Kr/NH3 Si3N4 is three times larger than that of the Ar/NH3 Si3N4. Furthermore the TDDB characteristics of Si3N4 on (1 1 0)Si are same as those of Si3N4 on (1 0 0)Si.
Keywords: Si3N4; MNS; Reliability; Krypton; Insulator; Si surface orientation; Plasma nitridation;

Electronic structure and energy band offsets for ultrathin silicon nitride on Si(1 0 0) by Seiichi Miyazaki; Masahiro Narasaki; Atushi Suyama; Masanori Yamaoka; Hideki Murakami (252-257).
For the interfaces of CVD Si3N4 on Si(1 0 0) and directly-nitrided Si(1 0 0), chemical bonding features, energy band offsets and defect state density distributions have been studied using high-resolution X-ray photoelectron spectroscopy and total photoelectron yield spectroscopy. At nitride–Si(1 0 0) interfaces, SiN bonding states in which each Si atom is bonded with one or three N atoms are formed predominantly, being presumably related to the structural strain induced by SiN bonding at the interface. For nearly stoichiometric SiN x (x≥1.3) in the thickness range of 1.0–17 nm which was prepared by 750 °C CVD or 700 °C direct-nitridation, the energy band gap was determined to be 5.4±0.1 eV from the energy loss spectra of N 1s photoelectrons. By analyzing the valence band spectra of thin SiN x /Si(1 0 0) heterostructures, the valence band offset between such SiN x and Si(1 0 0) was obtained to be 1.9±0.1 eV. For the direct-nitridation of Si(1 0 0) at 600 or 700 °C, an interface state density as low as ∼1010  eV−1  cm−2 near Si midgap was confirmed by total photoelectron yield measurements.
Keywords: Silicon nitride; Band offset; Energy band gap; Photoelectron spectroscopy; Defect density;

The role of hydrogen migration in negative-bias temperature instability by Jiro Ushio; Kikuo Watanabe; Keiko Kushida-Abdelghafar; Takuya Maruizumi (258-263).
The role of hydrogen in negative-bias temperature instability (NBTI) at Si/SiO2 and Si/SiO x N y interfaces was investigated by using molecular models of the interfaces and first-principles calculations. The results suggest that the hydrogen is likely to migrate as an electrically neutral atom rather than a proton. It was found that the hydrogen migration at the Si/SiO x N y interface lowers the hole-trapping reaction energy, while that at the Si/SiO2 interface makes it higher. This means that the more severe NBTI at the Si/SiO x N y interface compared to that at the Si/SiO2 interface is caused by the migrated hydrogen.
Keywords: NBTI; Density functional theory; Interface; Hydrogen; Water;

New intrinsic pair defects in silicon dioxide interface by Isao Kitagawa; Takuya Maruizumi (264-269).
Oxygen vacancy (OV) and peroxy linkage (PX) pairs in silicon dioxide are investigated using ab initio density functional calculations. We find that the pair defects in which the peroxy linkage is located adjacent to the oxygen vacancy have an electron-trapped thermodynamic charge state level in the silicon band gap and that the geometrical structure of the electron-trapped level is the asymmetrical double SiOSi bond structure of the pair defect.
Keywords: Oxygen vacancy; Peroxy linkage; Pair defect; Thermodynamic charge state level; Ab initio calculation;

Microscopic mechanism of interfacial reaction during Si oxidation by Toru Akiyama; Hiroyuki Kageshima (270-274).
The reaction of atomic oxygen at the SiO2/Si(1 0 0) interface is studied based on total-energy electronic-structure calculations. It is found that the reaction in which an O atom in the oxide inserts into the SiSi bond of the substrate is largely exothermic. The calculated energy barrier of 0.87 eV for this reaction is lower than the experimentally reported activation energy (2.0 eV) for the interfacial reaction in the dry oxidation. The results would help us clarify the microscopic mechanism of Si oxidation, especially in identifying the form of oxidant in the dry oxidation.
Keywords: Si oxidation; SiO2/Si interface; Atomic oxygen; First-principles calculation; Energy barriers;

(0 0 1)-Oriented GaAs metal–insulator–semiconductor (MIS) structures having a silicon interface control layer (Si ICL) were fabricated on surfaces having Ga-rich (4×6) reconstructions. Si ICL was grown by molecular beam epitaxy. MIS structures were fabricated by partially converting Si ICL to SiN x by direct nitridation, and further depositing a thick SiO2 layer on top as the main passivation dielectric by plasma-assisted chemical vapor deposition. Reflection high-energy electron diffraction, in situ X-ray photoelectron spectroscopy and MIS capacitance–voltage (CV) techniques were used for characterization. The initial surface reconstruction was found to have a surprisingly strong effect on the degree of Fermi level pinning at the MIS interface. In contrast to the standard As-rich (2×4) surface, which results in strongly pinned MIS interfaces, the novel SiO2/SiN x /Si ICL/GaAs MIS structures formed on “genuine” (4×6) surface realized complete unpinning of Fermi level over the entire band gap with a minimum interface state density of 4×1010  cm−2  eV−1 range.
Keywords: Surface passivation; GaAs; Fermi level pinning; MIS structure; (4 × 6) Surface; Surface passivation; CV method;

The compositional transition layer in SiO2/Si(1 0 0) interface is studied with high-resolution Rutherford backscattering spectroscopy (HRBS). The HRBS spectra of thin SiO2 films on Si, which are prepared by pyrogenic oxidation, are measured at various incident angles. The spectrum shows a sharp Si surface edge and a relatively broad edge corresponding to the SiO2/Si interface. The thickness of the compositional transition layer in the SiO2/Si interface and the energy loss straggling are determined simultaneously from the observed spectra. The obtained thickness of the transition layer is 0.53±0.08 nm. The obtained energy loss straggling agrees with the empirical formula given by Yang et al.
Keywords: SiO2/Si; Transition layer; High-resolution; Rutherford backscattering spectroscopy; Energy loss straggling;

Depth profiling of oxynitride film formed on Si(1 0 0) by photon energy dependent photoelectron spectroscopy by K. Nishizaki; H. Nohira; K. Takahashi; N. Kamakura; Y. Takata; S. Shin; K. Kobayashi; N. Tamura; K. Hikazutani; T. Hattori (287-290).
Si 2p and N 1s spectra arising from a oxynitride film formed on Si(1 0 0) surface were measured in the photon energy range from 556 to 1471 eV, where the electron escape depth in SiO2 changes from 1.68 to 3.80 nm. It was found for the first time that the photon energy dependence of N 1s and Si 2p photoelectron spectra can be nearly reproduced if the depth profile of nitrogen atoms is known.
Keywords: Depth profiling; Photoelectron spectroscopy; Synchrotron radiation; Oxynitride;

Interfacial chemistry and structures of ultrathin Si oxynitride films by M. Oshima; K. Kimura; K. Ono; K. Horiba; K. Nakamura; H. Kumigashira; J.-H. Oh; M. Niwa; K. Usuda; N. Hirashita (291-295).
Ultrathin SiON films with different nitrogen profiles grown by the plasma-enhanced CVD method and the rapid thermal nitridation (RTN) of SiO2 with an NO gas have been analyzed by high-resolution angle-resolved photoelectron spectroscopy using bright synchrotron radiation to investigate interfacial chemistry and in-depth distribution of nitrogen atoms based on the second nearest neighbor effect of N 1s chemical shift. It is found that the CVD-deposited SiON film has a three-layer structure consisting of homogeneously-distributed N atoms in the [Si-Si3−x N x ]3N chemical state, N atoms in the (SiSi3−x O x )3N chemical state of about two monolayers, and the top SiO2 layer. In contrast, N atoms in the NO-RTN SiON film exist at the SiON/Si interface as a double layer consisting of the [Si-Si3−x N x ]3N lower layer and the (SiSi3−x O x )3N upper layer with the concentration of 3.9×1014 and 1.7×1014  cm−2, respectively, based on the N 1s chemical shift of about 0.6 eV.
Keywords: Interfacial chemistry; Ultrathin Si oxynitride films; Photoelectron spectroscopy; Interfacial structures;

Preparation of hafnium oxide films from oxygen-free Hf[N(C2H5)2]4 precursor and their properties by Kenji Takahashi; Makoto Nakayama; Shintaro Yokoyama; Takeshi Kimura; Eisuke Tokumitsu; Hiroshi Funakubo (296-301).
Hafnium oxide films were deposited on silicon substrates at the deposition temperature ranging from 190 to 450 °C by metalorganic chemical vapor deposition (MOCVD). An oxygen-free precursor, Hf[N(C2H5)2]4, and O2 gas were used as starting materials. Deposition rate increased by the addition of O2 gas but was centrally decreased by the excess O2 addition due to the gas phase reaction at the temperature of 360 to 400 °C. Hafnium oxide films deposited at 400 °C consisted of amorphous phase and noticeable carbon and nitrogen contamination was not detected by X-ray photoelectron spectroscopy (XPS). From the relationship between the reciprocal of accumulation capacitance and physical thickness, and the cross-sectional high-resolution transmission electron microscope (HRTEM) observation, the relative dielectric constant of the hafnium oxide layer and the interfacial layer were estimated to be 16.4 and 7.8, respectively. The relative dielectric constant of the interfacial layer was much higher than silicon oxide and was closely related to the oxygen-free characteristics of hafnium precursor. This high dielectric constant (high-κ) interfacial layer is beneficial in decreasing the equivalent oxide thickness value.
Keywords: Hafnium oxide; High dielectric constant; Chemical vapor deposition;

Effect of surface treatment of Si substrates and annealing condition on high-k rare earth oxide gate dielectrics by C. Ohshima; J. Taguchi; I. Kashiwagi; H. Yamamoto; S. Ohmi; H. Iwai (302-306).
Effect of chemical oxide and low temperature long time annealing on the electrical characteristics for rare earth oxides deposited on Si(1 0 0) were investigated.Formation of chemical oxide on Si substrates prior to the Gd2O3 depositions was found to decrease the leakage current significantly compared the films deposited on HF-last Si substrate, when the thickness was 3.5 nm or thicker, while the effect was not observed when the thickness was 2.8 nm. Annealing at 400 °C for 90 min also decreased leakage current of Dy2O3 thin films with little increase of capacitance equivalent thickness (CET).
Keywords: High-k gate dielectric; Rare earth oxides; MBE; Interfacial layer; Chemical oxide; Low temperature long time annealing;

Si/SiO2 interface attack during metal oxide growth under low oxygen pressure by K. Kubo; M. Kiyohara; K. Shimoyama; K. Yamabe (307-311).
The growths of BaTiO3 films on interfacial SiO2 were carried out with molecular beam epitaxy (MBE) in various oxygen partial pressures. In the BaTiO3 growth on 2 nm-thick SiO2 film at the oxygen partial pressure of less than 4.8×10−5  Pa, concavities at the BaTiO3 film surface and the Si/SiO2 interface appeared and the Si atoms diffused from the Si substrate to the top BaTiO3 layer. These were observed only after the film growth in the low oxygen pressure and only on ultrathin interfacial SiO2. And the silicide material was formed within the concavity. These results indicate that 2 nm-thick SiO2 film is not enough to the suppression of the reaction of the metal atoms with Si substrate.
Keywords: BaTiO3; Silicide; SiO2; Si; Interface; Concavity;

An orientation ratio and ferroelectric properties of ultra-thin PTO films by K. Nishida; T. Sugino; M. Osada; M. Kakihana; T. Katoda (312-317).
The relationship among crystallographic orientation and quality, flatness of a surface, electrical properties and thickness for lead titanate (PbTiO3: PTO) ultra-thin films is reported. A crystallographic orientation changed from (1 0 0) to (0 0 1) with an increase in film thickness. However, a (0 0 1) plane orientation ratio α saturated to 0.85 and root square mean (RMS) of flatness saturated to 1.4 nm when the film thickness was approximately 90 nm. A PTO film thinner than approximately 90 nm had a larger dielectric constant and that thicker than approximate 90 nm showed ferroelectric property.
Keywords: PTO; Ferroelectrics; Substrate; Film orientation; PE property;

Effects of the substrate on properties of PTO thin film by K. Nishida; G. Matuoka; M. Osada; M. Kakihana; T. Katoda (318-322).
The lead titanate (PbTiO3: PTO) films grown by PE-CVD had (0 0 1) and (1 1 1) orientations on the substrates of Pt(1 0 0)/MgO(1 0 0) and Pt(1 1 1)/MgO(1 1 1) while the PTO film had (1 0 0) orientation on the Pt(1 1 1)/MgO(1 0 0) substrate. The PTO thin film with (0 0 1) orientation had the best flatness. The PTO film on the Pt(1 0 0)/MgO(1 0 0) substrate having the crystallographic orientation corresponding to the polarization direction showed a ferroelectrical hystersis loop.
Keywords: PTO; Ferroelectrics; Substrate; Film orientation; PE property;

Growth mechanism of PTO on MgO at initial stage by K. Nishida; K. Shirakata; M. Osada; M. Kakihana; T. Katoda (323-328).
Growth mechanism of a lead titanate (PbTiO3, PTO) thin film at the initial stage has been made clear. The mechanism is strongly affected by accumulation and release of stress. Flatness of the surface and the crystallographic orientation of the PTO film change with growth mode.
Keywords: PTO; Growth mechanism; Residual stress; Surface roughness; Film orientation;

Thickness dependent integrity of gate oxide on SOI by Mikio Tsujiuchi; Toshiaki Iwamatsu; Hideki Naruoka; Hiroshi Umeda; Takashi Ipposhi; Shigeto Maegawa; Yasuo Inoue (329-333).
To investigate the gate oxide integrity for the silicon-on-insulator (SOI) wafer, we evaluated the time-dependent dielectric breakdown (TDDB) characteristic of gate oxide formed on SOI wafer with gate oxide thickness (T ox) as a parameter. The TDDB characteristic was degraded with increasing the T ox of gate oxide for the SOI wafer. The time to 50% failure of breakdown (T BD) was shorter when T ox was thicker than 7 nm in contrast to the gate oxide for the bulk silicon wafer.
Keywords: SOI; SIMOX; TDDB; GOI; Threading dislocation;

We demonstrate an all-optical circular polarization switching (AOCPS) phenomenon by using the storing polarization effect in a photo chemically etched silicon (PCE Si). The luminescence, structural and, chemical characteristics of the PCE Si are also observed, and are compared with the porous silicon (PS). In addition, the mechanism of an AOCPS phenomenon is discussed in terms of interaction between spinning electrons and circularly polarized photons.
Keywords: AOCPS; Photo chemically etched silicon; Porous silicon;

Simulation of dislocation accumulation in ULSI cells with STI structure by Tetsuya Ohashi; Michihiro Sato; Takuya Maruizumi; Isao Kitagawa (340-346).
Periodic structure of the shallow trench isolation (STI) type ULSI cells is generally used for the latest semiconductor devices. However, dislocations sometimes accumulate in the electron channel when the device size becomes small, and they have an enormous effect on the electronic state and obstruct the device from normal operation. In this paper, we numerically model the periodic structure of the STI type ULSI cells, and analyze the plastic slip that takes place during the oxidation process of oxide film area. The slip deformation is analyzed by a crystal plasticity analysis software, which has been developed on the basis of finite element technique, and we evaluate the accumulation of dislocations that accompany plastic slip. The results show stress concentrations at the shoulder part of the device area and the bottom corners of the trench for the device isolation, and the high stresses at these area cause plastic slip and dislocation accumulation. The direction of these dislocation lines are shown to be mostly parallel to the trench direction and dislocations are approximately 60° mixed type.
Keywords: ULSI; Shallow trench isolation; Dislocation; Crystal plasticity analysis; Finite element method;

We present the improvement of hot-carrier-reliability by deuterium annealing at the temperatures ranging from 430 to 460 °C in the case of CMOS transistors of the design rule of 0.13 μm. By means of secondary ion mass spectroscopy (SIMS) and ESR measurements, we confirm that this improvement is caused by the termination of the interface defects by deuterium atoms.
Keywords: Hydrogen termination; Deuterium; Silicon; Interface defect; Hot-carrier-reliability;

The dielectric constant of ultrathin (0.55–7.96 nm) SiO2 films formed on Si(0 0 1) substrates was characterized in terms of the modified Auger parameter, α′. The α′ values for Si atoms were found to shift by about 0.7 eV for ultrathin SiO2 films compared with thick SiO2 films. This shift is apparently caused only by a change in the electrostatic screening energy originating from the dielectric discontinuity between the bulk dielectric constants of SiO2 and Si at the SiO2/Si interface. This indicates that the bulk dielectric constant also holds for ultrathin SiO2 films.
Keywords: SiO2; Si; Dielectric constant; XPS; AES; AES parameter;

Structural study of SiC(0 0 0 1)3×3 surface by surface X-ray diffraction by T. Aoyama; K. Akimoto; A. Ichimiya; Y. Hisada; S. Mukainakano; T. Emoto; H. Tajiri; T. Takahashi; H. Sugiyama; X. Zhang; H. Kawata (356-360).
Surface structure of 6H-SiC(0 0 0 1)3×3 reconstruction has been studied by grazing incidence X-ray diffraction with synchrotron radiation. We compared the Patterson map obtained from experimental structure factors with calculated Patterson maps estimated from the models that had been proposed. As the result, the calculated Patterson maps of Kulakov et al.’s [Surf. Sci. 346 (1996) 49] and Starke and coworkers’ models [Phys. Rev. Lett. 80 (1998) 758; Phys. Rev. B 58 (1998) 10806; Surf. Rev. Lett. 6 (1999) 1129; Appl. Surf. Sci. 162–163 (2000) 9; Phys. Rev. B 62 (2000) 10335] are relatively in good agreement with experimental one. Therefore, we conclude that there is high possibility that either Kulakov et al.’s or Starke and coworkers’ models are reasonable as the actual 3×3 structure.
Keywords: X-ray diffraction; Reconstructed structure; SiC;

In situ observation of step-terrace structures on MOVPE grown InP(0 0 1) by using grazing X-ray scattering by T. Kawamura; S. Bhunia; Y. Watanabe; S. Fujikawa; J. Matsui; Y. Kagoshima; Y. Tsusaka (361-364).
Step-terrace structures on MOVPE grown InP(0 0 1) surface were investigated by using grazing X-ray scattering. After buffer layers were formed on the substrate, X-ray scattering profiles were measured in the same chamber without exposing the sample to air. Small peaks were observed at the tail of the specular reflections, suggesting the in-plane periodicity of surface morphology. The azimuth angle dependence of peak position suggests a one-dimensional structure on the surface, and considering the AFM images of the sample, the bunched step-terrace structure toward [1 0 0] is the reason of this structure. Analyses based on a simple grating approximation shows the period of the one-dimensional structure is about 550 nm, which is consistent with the spacing value determined from AFM images.
Keywords: MOVPE; Semiconductors; III–V; Surface morphology; X-ray scattering; Surface step;

SiO2/SiC interface proved by positron annihilation by M. Maekawa; A. Kawasuso; M. Yoshikawa; H. Itoh (365-370).
We have studied positron annihilation in a Silicon carbide (SiC)–metal/oxide/semiconductor (MOS) structure using a monoenergetic positron beam. The Doppler broadening of annihilation quanta were measured as functions of the incident positron energy and the gate bias. Applying negative gate bias, significant increases in S-parameters were observed. This indicates the migration of implanted positrons towards SiO2/SiC interface and annihilation at open-volume type defects. The behavior of S-parameters depending on the bias voltage was well correlated with the capacitance–voltage (CV) characteristics. We observed higher S-parameters and the interfacial trap density in MOS structures fabricated using the dry oxidation method as compared to those by pyrogenic oxidation method.
Keywords: SiO2/SiC interface; MOS structure; Positron beam; Doppler-shift; Open-volume defect;

Study of Cu and Co gettering mechanism using radioactive isotope tracers by Kazuhito Matsukawa; Hideki Naruoka; Nobuyoshi Hattori; Yoji Mashiko (371-375).
The gettering mechanism of Cu and Co in various wafers has been quantitatively studied by the measurement of Cu and Co distribution using radioactive isotope tracer method. We found quantitative gettering of Cu and Co in P/P+ epitaxial wafer with polyback seal (PBS) and bulk micro defect (BMD), respectively. On the other hand, P+ substrate was not an effective gettering site for Co because of no Coulomb interaction between Co0 and high boron in the substrate of epitaxial wafer. In the case of Cu, the high boron concentration in the substrate of P/P+ epitaxial wafer without PBS has a strong gettering effect due to Coulomb interaction.
Keywords: Gettering; Radioactive isotope tracer; Bulk micro defect; Copper; Epitaxial wafer; Cobalt;

Nucleation and growth of nanocrystalline silicon studied by TEM, XPS and ESR by Keisuke Sato; Tomio Izumi; Mitsuo Iwase; Yoshiyuki Show; Hiroshi Morisaki; Toshie Yaguchi; Takeo Kamino (376-381).
Nucleation and growth process of nanocrystalline silicon (nc-Si) formed by radio frequency (RF) sputtering method and subsequently thermal treatment has been studied by using high resolution-transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) methods. Silicon (Si) atoms in amorphous sub-oxide (a-SiO x ) film were coagulated to form nc-Si with diameter of approximately 1.5 nm in the film after annealing at 900 °C. The size and number of nc-Si increased with the increase of the annealing temperature. The average size of nc-Si observed at annealing temperature of 1100 °C was 2.5 nm. We also observed nc-Si with high pressure phase in the annealed sample.
Keywords: Nanocrystalline silicon; Amorphous SiO x ; High resolution-transmission electron Microscope; X-ray diffraction; X-ray photoelectron spectroscopy; Electron spin resonance;

Real-time measurement of rocking curves during MOVPE growth of Ga x In1− x P/GaAs by S. Bhunia; T. Kawamura; Y. Watanabe; S. Fujikawa; J. Matsui; Y. Kagoshima; Y. Tsusaka; K. Uchida; N. Sugiyama; M. Furiya; S. Nozaki; H. Morisaki (382-387).
Measurement of real-time rocking curves of semiconductor heterostructures at various stages of metal organic vapor epitaxy (MOVPE) process may provide useful informations about the composition, thickness and in-built strain in the growing epilayer. In this study, we have used a previously grown lattice-matched GaInP/GaAs heterostructure as the reference substrate on which Ga x In1−x P epilayers of different composition and thickness were successively grown by MOVPE while recording rocking curves of each layer in real-time during the growth by using synchrotron X-ray source. Strain redistribution at the interface of the GaInP/GaAs substrate due to the different linear thermal expansion coefficients of GaInP and GaAs was determined from rocking curve of the heterostructure measured at 570 °C. We could detect the change in rocking curve due to the growth of as thin as 16 nm of In-rich Ga0.42In0.58P epilayer at the initial stage of growth. Data from the simulation of each intermediate rocking curve during growth was systematically used to grow a lattice-matched GaInP epilayer. We believe, this is the first report of measurement of rocking curves at high temperature and during MOVPE growth of Ga x In1−x P.
Keywords: GaInP; Real-time; Rocking curve; MOVPE; Synchrotron radiation;

We present the results of an experimental investigation of initial thermal oxidation of the Si(0 0 1) surface at the surface temperature of 860 and 895 K in the O2 pressure of 1×10−4  Pa. The time evolution of Si oxidation states was measured by real time in situ Si-2p photoemission spectroscopy with high energy-resolution synchrotron radiation. The changes of each oxidation state (Si1+, Si2+, Si3+ and Si4+) were clearly monitored. The Si4+ oxidation state was observed even in the early stage of oxidation after the appearance of Si3+ species. These oxidation states have appeared in order of the low oxidation number. The onset of Si4+ species at 895 K appeared quickly comparing with that at 860 K, indicating the fast diffusion process of adsorbed oxygen atoms.
Keywords: Real time observation; Synchrotron radiation photoemission spectroscopy; Passive oxidation; Si(0 0 1) surface; O2 gas; Si oxidation states;

Real-time monitoring of oxidation on the Ti(0 0 0 1) surface by synchrotron radiation photoelectron spectroscopy and RHEED–AES by Y. Takakuwa; S. Ishidzuka; A. Yoshigoe; Y. Teraoka; Y. Yamauchi; Y. Mizuno; H. Tonda; T. Homma (395-401).
The oxidation kinetics on the Ti(0 0 0 1) single crystal surface was investigated by real-time Auger electron spectroscopy combined with reflection high-energy electron diffraction (RHEED–AES) and high-resolution photoelectron spectroscopy using synchrotron radiation. The RHEED specular reflection spot intensity showed an oscillatory behavior, at the maxima and minima of which the oxygen uptake curve obtained by O KLL Auger electron intensity shows breaks. This agreement indicates that growth of oxides progresses with changing the surface morphology and the oxygen uptake rate. The O2 dose dependence of Ti 2p photoelectron spectrum measured at photon energies of 574.6 eV (surface sensitive) and 1549 eV (bulk sensitive) revealed that (1) oxidation of metallic Ti atoms with growing Ti2O and TiO on the surface makes the surface morphology roughened up to ∼17 L; (2) the roughened morphology is recovered by oxidation of Ti2O and TiO into Ti2O3, Ti3O5 and TiO2 up to ∼45 L; (3) after almost saturation of TiO2 growth in the surface layer the surface morphology is roughened again by further oxidation at the interface up to ∼140 L; and (4) then the oxygen uptake rate is considerably suppressed due to the passivation effect of grown oxides.
Keywords: Titanium; Oxidation; Auger electron spectroscopy; Reflection high-energy electron diffraction; Photoelectron spectroscopy; Synchrotron radiation; Surface chemical reaction;

Formation and characteristics of 100-nm scale GaAs quantum wires by selective area MOVPE by H Takahashi; Y Miyoshi; F Nakajima; P Mohan; J Motohisa; T Fukui (402-406).
We fabricated quantum wires (QWRs) with sub-micron wire width using GaAs/AlGaAs selectively doped structures grown by selective area metalorganic vapor phase epitaxy (SA-MOVPE) on (0 0 1) masked GaAs substrates partially covered by SiON. From the measurement of a two-terminal conductance as a function of geometrical wire width, QWRs with effective channel width <100 nm are formed without application of any gate bias. The magnetoresistance measurement at 1.7 K also suggests the formation of narrow QWRs, although it also indicates a presence of potential fluctuation along the QWRs. The effective channel width of present QWRs are much narrower than the previously reported values (∼300 nm) of those formed by SA-MOVPE.
Keywords: Single electron transistor; SA-MOVPE; Quantum dot; Quantum wire; GaAs; Magnetoresistance;

Three-dimensional (3D) InAs dots were formed from 2D layers by annealing. Critical thickness (CT) of 2D–3D transition due to annealing was studied, and it was found that this shape transition depends on the growth condition of the 2D InAs layers, which changes the surface structure of the 2D layers. The formation mechanism of the 3D dots was kinetically explained by desorption of indium species from step edges and their aggregation near the steps.
Keywords: Self-assembled quantum dots; Stranski-Krastanov growth; Annealing; Critical thickness; Multi-nucleation;

Fabrication and characterization of GaInP/GaAs triple barrier resonant tunneling diodes grown by MOCVD by Naoya Asaoka; Hiroki Funato; Michihiko Suhara; Tsugunori Okumura (413-418).
GaInP/GaAs triple barrier resonant tunneling diodes (TBRTDs) grown by metal organic chemical vapor deposition were fabricated. Temperature dependence of current–voltage characteristics was measured from 18.6 to 294.1 K and negative differential resistance was observed up to 167 K. From the temperature dependence of peak voltage, peak current, valley voltage, and valley current, we estimated that the NDR characteristic of the TBRTDs is due to alignment and misalignment of quantum levels of left and right well at energy close to the conduction band bottom.
Keywords: GaInP/GaAs heterostructure; Triple barrier resonant tunneling diodes; PdGe Ohmic contact;

Precise control of size and density of self-assembled Ge dot on Si(1 0 0) by carbon-induced strain-engineering by Y. Wakayama; L.V. Sokolov; N. Zakharov; P. Werner; U. Gösele (419-423).
In order to produce dome-shaped Ge dots with small size and high density, C submonolayers (C-SMLs) were incorporated at the interface between Ge wetting layers and Ge dots. The C atoms are considered to induce a local strain field by forming Ge–C bonding. Such strain field enhanced dome formation even at low temperature (<500 °C). Optimization of experimental conditions enabled precise control of the Ge dome size in the range of 30–40 nm with the density of 1010  cm−2. The Ge domes thus prepared exhibited intensive photoluminescence (PL) compared to those prepared by a conventional self-assembling technique.
Keywords: Si; Ge; Quantum dot; Strain-engineering; Photoluminescence;

We have previously proposed a Si sub-atomic layer epitaxy (SALE) method with which Si digital epitaxy from non-cracked Si2H6 is realized at a growth rate of ∼0.63 ML/cycle by repeating submonolayer Si saturation adsorption and adatom migration induced by surface thermal excitation. By the use of thermally-cracked Si2H6 in gas phase, the Si saturation coverage on Si(0 0 1) approaches ∼1 ML and Si atomic layer epitaxy on Ge(0 0 1) has also been achieved (thermally-cracked hydride molecule (TCH)–atomic layer epitaxy (ALE)) in the initial ALE cycles. The adsorption mechanisms are analyzed by scanning tunneling microscope (STM) and hydrogen temperature-programmed desorption (TPD) techniques together with the Si coverage measurement and :SiH2 production rate analysis. The results are systematically understood and :SiH2 produced through gas-phase Si2H6 thermal cracking nearly self-limitedly adsorbs on Si(0 0 1) by ∼1 ML. From the STM image analysis, the :SiH2 is interpreted to orderly adsorb on each of the two dangling bonds of the dimer.
Keywords: Atomic layer epitaxy; Surface processes; Adsorption; Silicon; Disilane; Self-limiting;

Characteristics of ZnO whiskers prepared from organic-zinc by J. Kubota; K. Haga; Y. Kashiwaba; H. Watanabe; B.P. Zhang; Y. Segawa (431-435).
ZnO micro-whiskers were successfully prepared by oxidizing of sublimated zinc acetylacetonate (Zn(C5H7O2)2) products. Crystallinity of ZnO whiskers was considerably improved by increasing thermal oxidation temperature. Full width at half maximum (FWHM) of ZnO (1 0  1 ̄  1) plane peak observed in the X-ray diffraction was 0.186°. SEM images of the whiskers oxidized at 1000 °C were a bundle of very fine whiskers and almost uniform for surface morphology. Room temperature photoluminescence (PL) spectrum of the whiskers oxidized over 400 °C shows a blue emission at wavelength of 420 nm. In the low temperature (4.2 K) PL spectrum of the ZnO whiskers oxidized over 800 °C, the emission from exciton bound to natural donor and that from free-exciton recombination were observed at 3.361 and at 3.376 eV, respectively.
Keywords: ZnO; Zn(C5H7O2)2; Whisker; Oxidation; Annealing; Photoluminescence;

We demonstrate the use of density-functional theory (DFT) calculations for understanding molecular beam epitaxy (MBE) of GaAs and InGaAs films at the atomic level. For analyzing island growth in homoepitaxy of GaAs(0 0 1), the use of DFT in conjunction with kinetic Monte Carlo (kMC) simulations is discussed. This approach enables us to elucidate the growth mechanisms of islands on the β2(2×4)-reconstructed surface and to compute the saturation values of the island density. Furthermore, DFT calculations are employed to investigate the stability of ultrathin InGaAs films on GaAs(0 0 1) as a function both of the chemical potential of arsenic in the growth environment, and of mechanical strain. Under very As-rich conditions, for deposition of two-thirds of a monolayer (ML) of InAs, our calculations indicate the formation of a (2×3)-reconstructed InGaAs(0 0 1) surface alloy. The calculated atomic structure is in excellent agreement with X-ray diffraction data. For less As-rich conditions and larger amounts of deposited InAs, we find InGaAs films with a α2(2×4) reconstruction to be most favorable.
Keywords: Growth simulations; Epitaxy; Formation kinetics of thin films; Diffusion and interface mixing;

Epitaxial growth of GaN(0 0 0 1) is possible even using molecular beam epitaxy (MBE). Under the N-rich condition, nitrogen adatom on GaN(0 0 0 1) truncated surface adsorbed at an abnormal site, H3-site which is not the original site for wurtzite structure nor zincblende structure. The nitrogen at the H3-site is very stable and inactive so that the epitaxial growth is prevented. The first-principles calculation shows us that the Ga-rich condition is very helpful to assist epitaxial growth of GaN(0 0 0 1).
Keywords: Molecular beam epitaxy; Epitaxial growth; Metal organic vapor phase epitaxy;

Thermodynamic study on compositional instability of InGaN/GaN and InGaN/InN during MBE by Yoshihiro Kangawa; Tomonori Ito; Yoshinao Kumagai; Akinori Koukitu (453-457).
Thermodynamic analyses were carried out to understand influence of lattice constraint from GaN and InN substrates on relationship between solid composition x of In x Ga1−x N films and input mole ratio R In (=P In 0/(P In 0+P Ga 0) where P i 0 is the input partial pressure of element i) during molecular beam epitaxy. The calculated results suggest that compositional unstable region is found at small R In region for InGaN on InN while that for InGaN on GaN can be seen at large R In region at higher temperatures. This implies that InN-rich thin films are possible to form on InN substrate though it is difficult to form on GaN substrate.
Keywords: Thermodynamic analysis; InGaN; MBE; Compositional instability; Contribution of lattice constraint;

Systematic theoretical investigations of miscibility in Si1−xy Ge x C y thin films by Tomonori Ito; Kohji Nakamura; Yoshihiro Kangawa; Kenji Shiraishi; Akihito Taguchi; Hiroyuki Kageshima (458-462).
Miscibility of C in Si1−xy Ge x C y thin films is systematically investigated by using the empirical interatomic potentials. The empirical potential approach is applied to calculate excess energies for Si1−xy Ge x C y thin films incorporating interface lattice constraint due to Si(0 0 1). In order to compare with experimental results, we employ the content values such as x=0.13, 0.22, 0.27, 0.31, 0.35, and y=0.019. The calculated results imply that the lattice constraint at the interface and SiC interatomic bond formation dramatically reduce excess energies of Si1−xy Ge x C y thin films by 20–30% of those in bulk state. Therefore, the lattice constraint promotes C incorporation in Si1−xy Ge x C y thin films. Furthermore, segregation phenomena of Ge and C atoms in Si0.78Ge0.2C0.02 on Si(0 0 1) is clarified by Monte Carlo (MC) simulation taking into account surface and interface structures. The simulated results reveal that Ge atoms segregate in the topmost layer and C atoms accumulate in the second layer. These calculated results suggest that the lattice constraint at the interface enhance the miscibility of C in Si1−xy Ge x C y thin films, whereas the miscibility tends to reduce near the surface because of the segregation of Ge and C atoms.
Keywords: Miscibility; Surface segregation; Si1−xy Ge x C y ; Thin films; Empirical potential calculations; Surface and interface contributions;

We adopt first-principle approach to calculate potential energy surfaces for α-quartz and -cristobalite silicon dioxide (SiO2) with hydrogenated impurities in the neutral, positive, and negative charged states. It is expected that H atoms in SiO2 have an important role to generate leakage current paths. In this paper, we calculate stable and unstable positions of a migrating H atom and discuss electrons or holes trapping mechanism. These results clarify that the dynamics of the H atom in the neutral, negative, and positive charged states should be different from one another, and therefore, the mechanism of the dielectric break down of SiO2 also depends on the charged environment. Based on the regional density functional theory, we have calculated the effective charge tensor density of the migrating H atom in the neutral state.
Keywords: Breakdown of SiO2; Hydrogenated impurity; Charge trapping; First-principle calculation; Potential energy surfaces; Molecular dynamics;

Ab initio study of 3C-SiC/M (M = Ti or Al) nano-hetero interfaces by Shingo Tanaka; Masanori Kohyama (471-477).
Ab initio pseudopotential calculation of 3C-SiC(1 1 1)/Al nano-hetero interfaces have been performed and interface atom species dependence (IASD) and interface orientation dependence (IOD) of nano-hetero interfaces between 3C-SiC ((1 1 1) or (0 0 1) orientation) and metal (Ti or Al) have been studied systematically. Stable atomic configurations of the 3C-SiC(1 1 1)/Al interfaces are quite different from those of the 3C-SiC(1 1 1)/Ti interfaces. Two terminated, Si-terminated (Si-TERM) and C-terminated (C-TERM), 3C-SiC(1 1 1)/Al interfaces have covalent bonding nature. In 3C-SiC/M (M = Ti or Al) nano-hetero interfaces, the C-terminated interface has relative strong, covalent and ionic CTi or CAl bonds as TiC or SiC while the Si-terminated interface has various type of bonding nature, relative weak SiTi or SiAl bonds from metallic character at the (0 0 1) interface to covalent character at the (1 1 1) interface. Adhesive energy (AE) shows strong IASD and IOD. The AE of the C-terminated interface is larger than that of the Si-terminated one. In the C-terminated interface, the AE of the (1 1 1) interface is smaller than that of the (0 0 1) one while in the Si-terminated interface there exists opposite interrelation. Schottky barrier height (SBH) also shows strong IASD and IOD. The SBH of the C-terminated interface is smaller than that of the Si-terminated one. The C-terminated SiC/Al interfaces have extremely small SBHs. In comparison with some experimental SBH, the present result is reliable as the difference of SBH between the two terminated interfaces and qualitative properties.
Keywords: Nano-hetero interface; Ab initio calculation; SiC; Schottky barrier height; Pseudopotential;

Dynamics of In atom during InAs/GaAs(0 0 1) growth process by A. Ishii; K. Fujiwara; T. Aisaka (478-482).
We calculated the dynamics of indium atom during the molecular beam epitaxy growth of InAs on GaAs(0 0 1) using the first-principle calculation. The result shows us that indium atom is very mobile. The hopping barrier energy of In is almost same as that of As on GaAs(0 0 1) surface. The substitution of In toward the substrate GaAs(0 0 1) also occurred, because the energy difference between the In atom on the second topmost layer and the substitution of it with the Ga atom of the fourth layer is very small. Thus, we should be careful to analyze experiments because indium atom is very active and mobile on GaAs(0 0 1) surface.
Keywords: Molecular beam epitaxy growth; Lattice-mismatch heterostructures; Quantum dots;

A field effect transistor using highly nitrogen-doped CVD diamond for power device applications by Yoko Yokoyama; Xueqing Li; Kuang Sheng; Andrei Mihaila; Tanija Traikovic; Florin Udrea; G.A.J. Amaratunga; Ken Okano (483-489).
A new idea of power device, which contains highly nitrogen-doped CVD diamond and Schottky contact, is proposed to actualise a power device with diamond. Two-dimensional simulation is conducted using ISE TCAD device simulator. While comparably high current is obtained in a transient simulation as expected, this current does not contribute to the drain–source current because of the symmetry of the device. Using an asymmetric structure or bias conditions, the device has high potential as an electric device for extremely high power, high frequency and high temperature.
Keywords: Highly nitrogen-doped CVD diamond; Schottky barrier; Power device; Carrier density;

Theoretical study on stable structures and diffusion mechanisms of B in SiO2 by Minoru Otani; Kenji Shiraishi; Atsushi Oshiyama (490-496).
We present first-principle total-energy calculations that clarify stable structures of B and mechanisms of B diffusion in SiO2. We find that a B atom takes a variety of stable and metastable geometries depending on its charge state. We also find that atomic rearrangements during the diffusion manifest a wealth of bonding feasibility in SiO2 and that the calculated activation energy agrees with the experimental data available.
Keywords: First-principle calculations; SiO2; Atomic boron; Energy barrier; Diffusion path; Boron penetration;

Epitaxial growth of 4H–SiC(0 3  3 ̄  8) and control of MOS interface by T. Kimoto; T. Hirao; K. Fujihira; H. Kosugi; K. Danno; H. Matsunami (497-501).
Homoepitaxial growth on 4H–SiC(0 3  3 ̄  8) by chemical vapor deposition (CVD) and the MOS interface have been investigated. Unintentionally-doped 4H–SiC(0 3  3 ̄  8) epilayers showed a low background doping concentration of 3×1014  cm−3 and a low trap concentration of 8×1011  cm−3. Almost complete (∼100%) closing of micropipes was realized, although some of very large (>3 μm) micropipes were threading into epilayers. Conductance measurements on n-type MOS capacitors revealed that the interface state density (D it) near the conduction-band edge is lower on 4H–SiC(0 3  3 ̄  8) than on 4H–SiC(0 0 0 1). Higher channel mobility was obtained for inversion-type (0 3  3 ̄  8) MOSFETs, compared to (0 0 0 1) MOSFETs.
Keywords: Silicon carbide; Epitaxy; Dislocation; MOS interface; Channel mobility; Wide bandgap semiconductor;

Growth of GaN on ZrB2 substrate by metal-organic vapor phase epitaxy by Yoshihito Tomida; Shugo Nitta; Satoshi Kamiyama; Hiroshi Amano; Isamu Akasaki; Shigeki Otani; Hiroyuki Kinoshita; Rong Liu; Abigail Bell; Fernando A. Ponce (502-507).
Growth of GaN by metal-organic vapor phase epitaxy (MOVPE) on metallic zirconium diboride (ZrB2) substrate was investigated. Cross-sectional transmission electron microscopy (TEM) showed that cubic ZrB x N1−x is formed on the surface when ZrB2 is exposed to ammonia-containing atmosphere, which protects the nucleation of GaN or AlN. We solved the problem by covering ZrB2 surface with very thin AlN or GaN at low temperature, thereby achieving high-quality GaN growth with a dislocation density less than 108  cm−2. Direct conduction was achieved through the back of ZrB2 and the surface of Si-doped GaN.
Keywords: MOVPE; ZrB2; GaN; Nitridation; New substrate;

Low-temperature growth of AlN on nearly lattice-matched MnO substrates by S. Ito; H. Fujioka; J. Ohta; A. Sasaki; J. Liu; M. Yoshimoto; H. Koinuma; M. Oshima (508-511).
We have investigated low-temperature epitaxial growths of AlN on nearly lattice-matched MnO(1 1 1) with pulsed laser deposition (PLD). Coaxial impact collision ion scattering spectroscopy (CAICISS) analysis has revealed that the surface of MnO(1 1 1) just before the growth consists of both the Mn-plane and the O-plane with a coverage ratio of 1:1. We have confirmed that the epitaxial growth temperature for AlN on MnO can be reduced down to 400 °C by the use of PLD. The roughness of the AlN/MnO interface decreased from 1.3 to 2.1 nm by the reduction of the growth temperature, which is probably due to the suppression of the intermixing reactions at the interface. On the contrary, the surface morphology of the AlN films was degraded by the reduction of the growth temperature probably due to the stress buildup caused by the suppression of the interface reactions.
Keywords: Group III nitrides; PLD; Hetero-epitaxy; Hetero-interface; CAICISS;

A very thin 1 μm-thick Al0.11Ga0.89N film is successfully separated from a sapphire substrate by thermal decomposition of interfacial region using high power laser, so-called laser lift-off technique. The used layer structure prior to the separation is 1.0 μm Al0.11Ga0.89N/0.3 μm GaN on sapphire grown by metal organic chemical vapor deposition (MOCVD), and third harmonic Q-switched Nd:YAG laser (λ=355 nm) is irradiated from the backside of the sapphire. Absorption of the laser light occurs only at the GaN interlayer and the decomposed thickness is limited up to the interlayer thickness. As a result, a crack-free thin AlGaN film is separated from sapphire with metal Ga underneath through the optimization of the process parameters. In contrast, removal of 2 μm-thick GaN single layer from sapphire is also tested, where peeling-off of the film with cracks is seen. In addition, slight red shift of the peak energy in the cathodoluminescence (CL) spectra of the AlGaN film is observed after the lift-off process, which is due to the relaxation of compressive stress in the film. Thus, separated AlGaN film is free from the disadvantages of using sapphire substrates such as the thermal mismatch, higher series resistance and poor heat dissipation so that it would enable high performance AlGaN-based ultraviolet (UV) light emitters.
Keywords: AlGaN; Sapphire; Removal; Laser lift-off; Cathodoluminescence;

Effects of hydrogen and nitrogen electron cyclotron resonance (ECR) plasma surface treatments on the current transport of two-dimensional electron gas (2DEG) at AlGaN/GaN interface were investigated by using a gateless heterostructure field-effect transistors (HFETs) test device. Current–voltage (IV) characteristics of the gateless device exhibited linear and saturation current behavior similar to that of a gated device, indicating presence of strong Fermi level pinning. As compared with the air-exposed surface, the current reduced significantly with appearance of hysteresis after H2-plasma treatment, whereas it slightly increased after N2-plasma treatment. After experiencing a positive pulse voltage, current in the H2-plasma-treated device dropped and then showed a fast exponential recovery followed by highly non-exponential slow recovery. Temperature dependence of initial recovery gave an activation energy of 0.37 eV. Observed current transients could be reproduced by numerical simulation assuming presence of dominant discrete near-surface deep donors and a U-shaped surface state continuum. X-ray photoelectron spectroscopy (XPS) analysis indicated near-surface reduction of N atoms after the H2-plasma treatment, indicating that the discrete states are related to N-vacancies. Since generation of N-vacancies is likely to occur in growth and processing of GaN-related materials, the present observation explains surface-related instabilities such as current collapse in AlGaN/GaN HFETs. For oxide removal, the N2-plasma treatment is much better than H2-plasma treatment, effectively removing oxides without producing defects.
Keywords: GaN; AlGaN; HFET; Plasma treatment; Current collapse; XPS;

Composition and stress dependences of InP/Ga x In1−x As y P1−y /InP interface structures were investigated using X-ray crystal truncation rod (CTR) scattering measurements, in order to realize why group-III atoms were always distributed widely around hetero-interfaces between InP and GaInAs(P). The result showed that the change of the Ga and As compositions to keep the lattice constants and the change of the stress to keep the Ga composition did not affect the degree of the distribution of the group-III atoms. It suggested that the distribution of the group-III atoms was due neither to mixing of In and Ga nor to relaxing local stress at around the interfaces. The distribution was probably related to the growth process at the surface in the organometallic vapor phase epitaxy (OMVPE) system.
Keywords: InP/GaInAsP/InP; X-ray CTR scattering; Interface structure; Distribution of group-III atoms;

Growth mechanism in heavily carbon-doped GaAs x Sb1−x grown by MOCVD by Yasuhiro Oda; Noriyuki Watanabe; Haruki Yokoyama; Takashi Kobayashi (532-536).
The InP/GaAsSb material system has type-II band structures and can provide ideal band structures for HBT operation. For the fabrication of HBTs, the growth of p-GaAsSb, which is used as a base layer in HBT structures, must be clarified. We investigated the change of GaAsSb growth behavior that occurs by adding CBr4 as a p-type dopant gas. As the CBr4 partial pressure in the vapor phase increased, the growth rate and Sb composition of the GaAsSb layer decreased. The CBr4 partial pressure dependence of growth rate is well interpreted by the formula derived from two chemical equilibrium equations: one the pyrolysis static reaction of CBr4, and the other the etching static reaction between HBr and Ga. From the fitting formula, GaSb in GaAsSb is found to be etched three times faster than GaAs in GaAsSb, resulting in a decrease of Sb composition in the GaAsSb solid phase with an increase of CBr4 partial pressure. Additionally, the growth rate of C-doped GaAsSb is found to be independent of the V/III ratio, although Sb composition in the solid phase monotonically decreased with increasing V/III ratio.
Keywords: MOCVD; III–V semiconductor; Type-II band structure; GaAsSb; Carbon doping; HBT;

AFM observation of OMVPE-grown ErP on InP substrates using a new organometal tris(ethylcyclopentadienyl)erbium (Er(EtCp)3) by T. Akane; S. Jinno; Y. Yang; T. Kuno; T. Hirata; Y. Isogai; N. Watanabe; Y. Fujiwara; A. Nakamura; Y. Takeda (537-541).
ErP has been grown on InP(0 0 1) substrates by organometallic vapor phase epitaxy (OMVPE) using a new liquid organic Er source: tris(ethylcyclopentadienyl)erbium (Er(EtCp)3). Morphological change of an ErP layer on InP(0 0 1) is investigated together with that of an overgrown capping InP layer. Optimum growth condition of InP causes islanding on over-monolayer-ErP. A relatively low overgrowth temperature of InP is a key factor for attaining complete capping coverage on ErP.
Keywords: ErP; Er(EtCp)3; InP; OMVPE; AFM;

The purpose of this study is to improve the output power (P out) and third-order inter-modulation distortion (IM3) of planar type GaAs power FET, which is used for RF power amplifiers for base stations of digital wireless communications systems. We focused on the GaAs surface state and attempted to improve the FET performance by intentional GaAs surface oxidation just prior to SiN cap deposition. Thermal or plasma oxidation has been found to improve P out and IM3 characteristics. Distinct improvement of FET performance was observed in intentionally oxidized FET, and the highest P out = 34 dBm and P out (@IM3=−55 dBc) = 23 dBm was measured on plasma oxidized FET with W g=5.2 mm. These results are shown in this article together with the results of photoelectron analysis.
Keywords: Surface state; Oxidation; Passivation film; Planar-type; MESFET;

Area-selective regrowth followed by AsH3 surface treatment and its application for ultra-shallow GaAs sidewall tunnel junctions by Takeo Ohno; Yutaka Oyama; Kenji Tezuka; Ken Suto; Jun-ichi Nishizawa (549-553).
Low-temperature (290 °C) area-selective regrowth (ASR) by the intermittent injection of triethylgallium (TEGa) and arsine (AsH3) in an ultra-high vacuum (UHV) was applied for the fabrication of ultra-shallow sidewall GaAs tunnel junctions with the junction area in the order of 10−8  cm2. Fabricated tunnel junctions have shown the record peak current density up to 35,000 A/cm2 at 100 μm long strip structure. It is shown that the tunnel junction characteristics are seriously dependent on the sidewall orientation and the regrown interface quality, which was determined by the surface treatment conditions under AsH3 just prior to regrowth. The junction characteristics and AsH3 surface treatment effects are discussed in view of the orientation dependence of Be doping and control of surface stoichiometry.
Keywords: Semiconductor homo- and hetero-interfaces; GaAs; Regrowth; Selective epitaxy; Tunnel junction; Sidewall;

A short-period Si/Si0.53Ge0.47 multiple quantum wells (MQW) was grown at 250 °C by synchrotron-radiation-excited chemical-beam epitaxy. Two-dimensional strained-layers with atomically abrupt interfaces were obtained. Atomic-scale roughness at the interfaces between the Si and Si0.53Ge0.47 layers is the main relaxation channel for misfit strain. The ellipsometric angles ψ and Δ exhibited short-period oscillations over time, which are the result of alternation of the top layer material. At transparent energy levels, long-period modulation caused by optical interference is superimposed on the shorter oscillations. Two different procedures for the real-time characterization of the MQW structure by fitting of simulation to the experimental data were investigated; one provided a wide-range fit to the long-period modulation where the whole MQW is approximated as a pseudo-dielectric film and the other was a local-fit, under virtual-interface approximation, to the short-period oscillation for the absorbent range of photon energy.
Keywords: Si/Si1−x Ge x multiple quantum well; Abrupt interface; Spectroscopic ellipsometry; Virtual-interface approximation; Interference fringe;

We have investigated interfacial characteristics of lattice-matched GaInP/GaAs heterostructures grown by low-pressure organometallic vapor phase epitaxy with constant and variable growth-temperature sequences. The 77 K photoluminescence (PL) measurements were used to confirm the existence of a lower-bandgap interlayer at the GaAs-on-GaInP interface. In the sample grown at 610 °C with the constant growth-temperature sequence, only a broad peak was observed at the wavelength longer than that expected from either GaInP or GaAs, while the PL spectrum was dominated by the GaAs near-band-edge emission in the sample grown at 550 °C. By inserting a thin 540 °C-grown GaInP layer into the GaAs-on-GaInP interface with the variable growth-temperature sequence, the interface-related PL peak was also suppressed completely.
Keywords: GaAs-on-GaInP interface; OMVPE; Sequence dependence; Photoluminescence;

Reactor structure dependence of interface abruptness in GaInAs/InP and GaInP/GaAs grown by organometallic vapor phase epitaxy by Yasufumi Fujiwara; Yoichi Nonogaki; Ryo Oga; Atsushi Koizumi; Yoshikazu Takeda (564-568).
We have grown Ga0.47In0.53As/InP and Ga0.51In0.49P/GaAs heterostructures by organometallic vapor phase epitaxy (OMVPE) using a multi-barrel reactor and compared their interface abruptness with that using a conventional single-barrel reactor. The multi-barrel reactor had a vertical four-barrel structure with five gas inlets, i.e. one inlet at the center in addition to one inlet for each barrel of four. In the growth, TBAs and TBP were used as group-V sources and supplied separately to barrels opposite to each other, while TEGa and TMIn as group-III sources were supplied from a center inlet to all the barrels. Secondary ion mass spectroscopy (SIMS) measurements on Ga0.47In0.53As/InP heterostructures reveled excellent abruptness of P distribution across the interface and negligible P contamination in the Ga0.47In0.53As layer. Such advantages have also been obtained in the Ga0.51In0.49P/GaAs system.
Keywords: Multi-barrel reactor; Heterointerface; Organometallic vapor phase epitaxy; GaInAs/InP; GaInP/GaAs;

Heteroepitaxial growth of InSb films on a Si(0 0 1) substrate via AlSb buffer layer by M. Mori; N. Akae; K. Uotani; N. Fujimoto; T. Tambo; C. Tatsuyama (569-574).
AlSb is a more suitable material as buffer layers for the heteroepitaxial growth of InSb films on a Si(0 0 1) substrate than Ge. It reduces the large lattice mismatch of about 19.3% between Si and InSb to about 5.6%. The resistance of AlSb with stoichiometric composition is large enough for the measurement of electrical properties. InSb films grown on the AlSb/Si(0 0 1) substrates by the co-evaporation of elemental indium (In) and antimony (Sb) sources were characterized by Auger electron spectroscopy (AES), X-ray diffraction (XRD) and atomic force microscopy (AFM), as a function of growth temperature. The thickness of grown InSb films was about 0.8–1.0 μm. The surface morphology and the crystal quality of the grown films strongly depend on growth temperature. It is found that the optimized growth temperature is about 300 °C to obtain the InSb films with smooth surface and good crystal quality.
Keywords: Heteroepitaxy; InSb; Si(0 0 1); AlSb buffer layer; AFM;

Initial stage of 3C–SiC growth on Si(0 0 1)–2 × 1 surface using monomethylsilane by Yuzuru Narita; Toshikazu Inubushi; Masayuki Harashima; Kanji Yasui; Tadashi Akahane (575-579).
The initial stage of cubic silicon carbide (3C–SiC) growth on Si(0 0 1)–2×1 surface was observed using monomethylsilane (MMS) as source gas at 650–750 °C by reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). The growth characteristics were compared with those in the case of dimethylsilane (DMS). Prior to the appearance of SiC spots, RHEED pattern of Si c(4×4) structure appeared, as in the case of DMS. From the variation in the RHEED intensity with time, the activation energy for the initial growth rate of SiC was very close to that in the case of DMS. From these facts, the rate determining step of the SiC initial growth was considered to be the same in both cases. From the AFM images of substrate surface after SiC nucleation, however, the surface morphology was different between the case using MMS and that using DMS.
Keywords: 3C–SiC; Initial stage of growth; Monomethylsilane; Dimethylsilane; RHEED; AFM;

Epitaxial growth of cubic silicon carbide (3C-SiC) on Si(1 0 0) and (1 1 1) substrates was carried out under various radio frequency (rf) powers by triode plasma CVD using dimethylsilane (DMS) as a source gas. The dependences of the film properties such as crystallinity and the formation of stacking faults on the rf power were investigated. Under low substrate temperatures, the crystallinity and the ratio of the domain including stacking faults of SiC were improved at rf power of about 60 W. On the other hand, those characteristics deteriorated by the application of the rf power at high temperature such as 1100 °C. The reason of such power dependences was discussed from the viewpoints of the impingement of charged particles and of the supply of hydrogen radicals.
Keywords: Silicon carbide; Triode plasma CVD; Dimethylsilane; Heteroepitaxy; rf power;

Mechanism of H2 pre-annealing on the growth of GaN on sapphire by MOVPE by Michinobu Tsuda; Kenichi Watanabe; Satoshi Kamiyama; Hiroshi Amano; Isamu Akasaki; Rong Liu; Abigail Bell; Fernando A. Ponce (585-589).
Pre-annealing of a sapphire substrate in hydrogen atmosphere strongly affects the growth of GaN by metalorganic vapor phase epitaxy using a low-temperature (LT) deposited AlN buffer layer. In order to grow high-quality GaN, the pre-annealing temperature should be higher than 900 °C. No annealing or low-temperature annealing results in the polycrystalline growth of GaN.
Keywords: GaN; MOVPE; H2-annealing; Sapphire substrate; Deoxidization;

Study of epitaxial SrTiO3 (STO) thin films grown on Si(0 0 1)–2 × 1 substrates by molecular beam epitaxy by M.N.K. Bhuiyan; A. Matsuda; T. Yasumura; T. Tambo; C. Tatsuyama (590-595).
Perovskite-type oxide SrTiO3 (STO) thin films with thicknesses of 30, 100, 300 and 1000 Å have been grown epitaxially on Si(0 0 1) substrates using co-evaporation of Sr and Ti in an O2 atmosphere of 9.0×10−8  Torr at 500 °C by molecular beam epitaxy (MBE). SrO buffer layers of 100 Å have been grown at 350 °C on Si substrates. The SrTiO3 films have been studied using reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD) and atomic force microscopy (AFM) as a function of the thickness of STO films. By heating the Si(0 0 1) substrates at 800 °C under Sr exposure for 2 min after the chemical cleaning and formation of protective SiO2 layer, RHEED patterns of the atomically clean Si(0 0 1)–2 × 1 surface have been observed. RHEED pattern becomes unclear after the growth of 30 and 100 Å-thick STO films. On the contrary, spotty and streaky patterns, and spotty patterns are observed clearly for 300 and 1000 Å-thick films, respectively. The surface crystallinity improves for all the samples after annealing at 800 °C. The STO films with thicknesses of 30 and 1000 Å consist of grains in the images of atomic force microscopy. The flatness and crystallinity of STO films with the thickness of 100–300 Å are better than the other films.
Keywords: STO film; Epitaxy; MBE; RHEED; AFM; Si;

Diamond films were homoepitaxially grown on type-Ib (1 0 0) diamond substrates by the microwave plasma CVD method at 800 °C with and without doping of S and compared with each other. Source gas was a mixture of H2+CH4 and a dopant gas of SF6, the doping amount ranging up to S/C ratio of 24,000 ppm. The FE-SEM image taken from grown films clearly revealed a morphological degradation when SF6 was doped uniformly during growth, and the more the doping amount, the more degradation developed. The SIMS observation exhibited a marked pile-up of S atoms at the interface between the grown layer and substrate, which was responsible for the morphological degradation. By introducing the Grading–Doping (starting from non-doping), a very smooth surface has been successfully obtained.
Keywords: Diamond film; Sulfur-doping; Epitaxial growth; SF6; Surface morphology; CVD;

Magnetic semiconductors have been investigated more and more actively, and have become a matter of interest for many researchers. To realize optical spintronic devices, it is strongly desirable that the semiconducting materials have magnetism with high Curie temperature as well as excellent optical (luminescence) properties. It is also necessary and of interest to create transparent magnetic semiconductors that can show optical emission. The magnetic and optical properties of a novel magnetic semiconductor, Cr-doped ZnO, were examined. All Cr-doped ZnO thin films were grown by the Ar–F excimer laser ablation (pulsed laser deposition, PLD) method. The room temperature photoluminescence peaks are very sharp and there is no deep-level emission. Prepared p–i–n diodes consisting of La0.85Sr0.15MnO3/SrTiO3/Zn1−x Cr x O triple-heterostructures exhibited clearly the rectifying IV curves.
Keywords: Magnetic semiconductor; Cr-doped ZnO; p–i–n diode; Oxide; Pulsed laser deposition;

Growth and annealing effect of ferromagnetic (Ga, Mn)As on Si(1 0 0) substrates by Naotaka Uchitomi; Sin’ya Sato; Yoshio Jinbo (607-613).
We describe the growth of diluted magnetic semiconductor (DMS) (Ga1−x , Mn x )As epitaxial layers on n-type Si(1 0 0) substrates using low-temperature-molecular beam epitaxy (LT-MBE). The Mn content of the (Ga1−x , Mn x )As layers was relatively high (6.2%). The ferromagnetic transition temperature T C was estimated to be 80 K for the as-grown film, and it strongly depended on the annealing temperature. The p-(Ga, Mn)As/n-Si heterostructures showing a ferromagnetic nature indicated a change in the sign of the Hall coefficient. We found that the transition temperature from n-type to p-type conduction considerably correlates with the T C.
Keywords: (Ga, Mn)As; Diluted magnetic semiconductor; Heterointerface; Low temperature MBE; Magnetotransport; III–V compound;

Growth of β-FeSi2 on MnSi1.7 layers by reactive deposition epitaxy by M. Kohira; Y. Souno; T. Matsuyama; H. Tatsuoka; I.J. Ohsugi; I.A. Nishida; H. Kuwabara (614-619).
The growth of ternary silicides and β-FeSi2 on ternary silicides for pseudobinary system MnSi1.7–β-FeSi2 was investigated by reactive deposition epitaxy (RDE). The structural properties of resultant silicide layers were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that a Fe x Mn1−x Si1.7 layer having a Mn11Si19 crystalline structure was formed when Fe was deposited within limited solubility range in MnSi1.7. On the other hand, β-FeSi2 islands were grown on Fe x Mn1−x Si1.7 layers when excess Fe atoms were deposited. The growth evolution and phase transitions of the silicide layers are discussed.
Keywords: A1 diffusion; A1 interfaces; A1 surface processes; B2 semiconducting silicon compounds;

Formation of CaMgSi at Ca2Si/Mg2Si interface by T. Hosono; M. Kuramoto; Y. Matsuzawa; Y. Momose; Y. Maeda; T. Matsuyama; H. Tatsuoka; Y. Fukuda; S. Hashimoto; H. Kuwabara (620-624).
The structural property and interfacial morphology have been investigated for the Ca2Si/Mg2Si interface. The Ca2Si layers were grown on Mg2Si layers by heat treatment of the Mg2Si/Si substrates in Ca vapor. It is found that the CaMgSi phase is formed at the Ca2Si/Mg2Si interface. The structural property of the resultant silicides was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The chemical composition of the layers was examined by energy dispersion spectroscopy (EDS). In addition, the chemical analysis by X-ray photoelectron spectroscopy (XPS) revealed the Mg segregation on the silicide surface. The growth mechanism of Ca2Si on Mg2Si/Si is also discussed.
Keywords: A1 diffusion; A1 interfaces; A1 surface processes; B2 semiconducting silicon compounds;

Decay rates of exciton and phonon-assisted recombination in asymmetric GaAs/AlAs type II superlattices by A.K Sulaimanov; L.S Braginsky; A.M Gilinsky; A.I Toropov; A.K Bakarov; K.S Zhuravlev (625-629).
Photoluminescence (PL) kinetics of X xy and X z excitons at the direct (AlAs-on-GaAs) and inverted (GaAs-on-AlAs) interfaces of asymmetric GaAs/AlAs (1 0 0) type II superlattices (SL) has been investigated. The kinetics of no phonon excitonic recombination is shown to be non-exponential. On the contrary, the kinetics of the phonon replicas follows an exponential law I(t)∝exp(−w ph t), where w ph for the inverted interface is about 1.4 times larger than that for the direct interface. The mean height and lateral size of roughness at the direct and inverted interfaces have been estimated from these data.
Keywords: Superlattices; Direct/inverted interface; Interface roughness; Exciton recombination; Luminescence kinetics; Decay rate;