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This work reports about influence of step bunching of SiC epitaxial-wafer surface on Fowler-Nordheim (F-N) tunneling emission current of SiC-MOS capacitor. We have measured the effective barrier height (ΦB) of SiO2/SiC interface, and estimated the deterioration factor of the effective ΦB on step bunching surface by calculating the local tunneling emission currents. Step bunching fluctuates the gate oxide thickness. The effective ΦB value can be successively derived using our proposed partitioned model in which constant ΦB value of flat surface is used. The fluctuation of the oxide film thickness results in the convergence of F-N tunneling emission currents at the thinner oxide in the MOS capacitor.

This work reports about effect of SiC epitaxial-wafer surface planarization by chemo-mechanical polishing (CMP) treatment on electrical properties of SiC-MOS capacitor. We have observed the surface morphology of 4H-SiC epitaxial layer planarized by CMP treatment using a confocal differential interference microscope, and evaluated the reliability of gate oxides on this surface using constant current time-dependent dielectric breakdown (CC-TDDB) and current-voltage (I-V) characteristics. Surface roughness such as step bunching deteriorates drastically the reliability of gate oxide, while the epitaxial-surface planarization by CMP treatment improved oxide reliability due to the high uniformity of the oxide film thickness.

The Integrated Evaluation Platform for SiC wafers and epitaxial films is established and provide TDDB reliability data such as Qbd. Accumulated numerous Qbd data derived from the platform shows three discrete universal distributions (D1>D2>D3) mainly affected by step bunching. On the fairly flat surface, locally spreading step-bunching area formation is caused by the scratches on the CMP surface. The step-bunching area contains large number of step-bunching lines, which correspond to trapezoid-shape defects, stretching in a low along the scratches. Only the downstream bases of the trapezoid-shape defects degrade the Qbd into D2 from D1 on the flat surface without step bunching.

Time-dependent dielectric breakdown (TDDB) measurement of MOS capacitors on an n-type 4 ° off-axis 4H-SiC(0001) wafer free from step-bunching showed specific breakdown in the Weibull distribution plots. By observing the as-grown SiC-epi wafer surface, two kinds of epitaxial surface defect, Trapezoid-shape and Bar-shape defects, were confirmed with confocal microscope. Charge to breakdown (Qbd) of MOS capacitors including an upstream line of these defects is almost the same value as that of a Wear-out breakdown region. On the other hand, the gate oxide breakdown of MOS capacitors occurred at a downstream line. It has revealed that specific part of these defects causes degradation of oxide reliability. Cross-sectional TEM images of MOS structure show that gate oxide thickness of MOS capacitor is non-uniform on the downstream line. Moreover, AFM observation of as-grown and oxidized SiC-epitaxial surfaces indicated that surface roughness of downstream line becomes 3-4 times larger than the as-grown one by oxidation process.

It has been widely accepted that wide-band-gap semiconductor SiC can provide low-loss semiconductor switches and diodes for the power electronics applications. The SiC devices enable the low-loss and compact converters and inverters.

It is well known that demonstratives are the cross-linguistically common source of third person pronouns due to the functional similarity between them. For this reason, they are morphologically related to or formally indistinguishable from one another in many languages. First and second person pronouns, on the other hand, typically have historical sources other than demonstratives. However, unlike the close relationship between demonstratives and third person pronouns, the fact that demonstratives and first/second person pronouns have a very tenuous diachronic relationship has not attracted much attention in previous studies. Based primarily on historical data from Japanese, the present study shows that there are at least three functional reasons why demonstratives do not usually give rise to first/second person pronouns. This study also discusses a limited context in which a demonstrative does develop into a second person pronoun.

Three phases, (Li x Mg 1− x ) 3 N 2− x (0 x x Mg 1− x ) 2 N (2− x )2/3 (0.5 x 3 N – Mg 3 N 2 system at 900 and 1000 K, and their crystal structures were investigated by applying the Rietveld method to the X-ray powder diffraction patterns. (Li x Mg 1− x ) 3 N 2− x crystallizes in a cubic superlattice ( a =9.9767(5) A at x =0.17). Mg atoms in the Mg 3 N 2 structure (space group Ia 3) were found to be partially replaced by Li atoms and the resultant structure was distorted with a lower symmetry space group I213 . The crystal structure of LiMgN (orthorhombic, a =7.1586(2), b =3.5069(8), c =5.01424(13) A, space group Pnma ) was determined ab initio from the X-ray powder diffraction data. It revealed a cation-ordered antifluorite-type structure. (Li x Mg 1− x ) 2 N (2− x )2/3 was prepared by rapid cooling from 1000 K to room temperature. It was also found to be stable at 900 and 1000 K and decomposed into LiMgN and Li 3 N on slow cooling in the furnace. Broad tails of the X-ray diffraction peaks suggest a modulated structure. A cation-disordered simple antifluorite type (space group Fm3m , a =4.99559(11) A at x =0.57) was proposed as the fundamental structure of (Li x Mg 1− x ) 2 N (2− x )2/3 .

Quantitative surface analysis includes the determination of the elemental composition and the structure of the sample under investigation. Although LEED, XPS, and SPM etc. have been used to investigate the surface structure of the materials, ambiguity remains in determining quantitatively the topmost atomic species and its alignment on an atomic scale. Therefore, we adopted coaxial impact collision ion scattering spectroscopy (CAICISS) to identify the terminating structure of compound materials such as SrTiO 3 (001), InP(001) etc. As a result of the measurements, we could determine the topmost atomic plane of those materials. CAICISS is considered to be a powerful tool for those topmost surface analysis of the materials.

The concept of the close-encounter probability was applied to simulate the angle-dependent surface peak intensities in coaxial impact collision ion scattering spectroscopy (CAICISS). It needs to follow incident trajectories only from a top surface up to several tens of monolayers below a surface and reduces the computing time remarkably. The simulation was performed for a polar-scan spectrum for TiO 2 -terminated SrTiO 3 (001) using 3 keV He + beams incident upon its (100) plane. This method reproduced well the observed polar-scan spectrum for Sr peak intensities except for grazing incidence less than 30°. On the other hand, the Williams' method, which has been frequently utilized, gave pronounced deviation due to neglect of the contributions from the depths. The applicability and limitation of the present method is discussed in detail.

We have synthesized a Monte Carlo program to simulate the time-of-flight (TOF) spectra of coaxial impact collision ion scattering spectroscopy (CAICISS). This program is based on the binary collision model considering inelastic energy loss and follows the incoming and outgoing trajectories for each incident ion from a top surface up to 300 monolayers (MLs) below a surface. The present simulation reproduced well the observed overall TOF spectra from MoS 2 (0001), whose surface structure was already known. It was also found that the ions backscattered from the atoms located in the depths from top surface down to 150th atom layer contributed to the TOF spectrum. In order to extract quantitative information on surface structures from CAICISS spectra, it is essential to estimate accurately the background originated from the backscattering at the depths. The CAICISS measurement followed by the Monte Carlo simulation was applied to structure analysis of a TiO 2 -terminated SrTiO 3 (001) surface prepared by a chemical treatment and confirmed that the topmost layer comprised a TiO 2 layer and the SrO fraction was estimated to be less than 5%.

The topmost atom of InP (001) surfaces, which were annealed at temperatures between 300 and 550°C or sputtered with 1 keV Ar+ at 300°C in ultra high vacuum, has been directly identified by means of coaxial impact collision ion scattering spectroscopy (CAICISS). Time-of-flight spectra of the annealed InP (001) surface exhibited both In and P peaks in both\([\overline {\text{1}} {\text{ }}10]\) azimuth and in [100] azimuth, which revealed that the topmost layer of annealed InP (001) was comprised of In-terminated and P-terminated surfaces. On the other hand, time-of-flight spectrum of the InP (001) sputtered at 300°C revealed only an In peak in\([\overline {\text{1}} {\text{ }}10]\) azimuth and revealed both In and P peaks in [100] azimuth. This result indicates that the topmost layer on the Ar+-sputtered InP (001) surface was completely terminated by In atoms. Furthermore, we indicate that surface damage induced by this sputtering treatment is little. The azimuthal depen-dence of CAICISS intensity scattered from In and P showed twofold symmetry with respect to [100] direction, which originated from the zinc-blende structure.

The terminating structure of 6H-SiC (0001) fabricated by the Acheson method was directly identified by means of Coaxial Impact Collision Ion Scattering Spectroscopy (CAICISS). The CAICISS spectra proved that the topmost surfaces of samples were Si-terminated planes for both the front and the rear faces. Furthermore, according to the azimuthal dependence of Si peak in TOF spectra, it was also proved that the (0001) Si face was composed of the Si-terminated flat terraces and steps whose height is 7.56 A corresponding to a half unit cell length of the c-axis of 6H-SiC.

Structural analysis and measurement of magnetic susceptibility were carried out for the 6H-type hexagonal compounds Ba3Cr2MO9 (M = Mo and W). The space groups of Ba3Cr2MoO9 and Ba3Cr2WO9 were determined by Rietveld analysis of powder X-ray diffraction data to be P63/mmc and P6 2c, respectively. Chromium ions were found to occupy the centers of face-shared octahedra, with tungsten or molybdenum ions at the centers of corner-shared octahedra. The magnetic susceptibilities of Ba3Cr2MoO9 and Ba3Cr2WO9 were explained using the two-sublattice and dimer models, respectively; the difference may be due to the difference in the valence states of Cr and Mo in Ba3Cr2MoO9 and Cr and W in Ba3Cr2WO9.

The hetero- and homoepitaxial deposition of GaAs films by the ionized cluster beam technique in connection with subsequent neutral beam deposition forming a double layer structure have been studied. It is found that ICB-deposited films have superior quality in comparison with conventional ion beam deposited films and comparable quality like MBE or MOCVD-deposited films. By the fabrication of device structures, it has been proved that the start of film growth from an interface formed by an ICB-deposited As layer is advantageous. Additionally, surface cleaning by low-energy ionized cluster beams has been studied. For the first time, defect-free surface cleaning by low-energy cluster ion beams has been realized.

Polycrystalline materials of BaSn1−xSbxO3−δ and Ba1−yLaySnO3−δ were prepared. Substitutional solubilities of antimony for tin and lanthanum for barium, respectively, in BaSnO3 were obtained to be x=0.18 for BaSn1−xSbxO3−δ and y

The surface structure of a Si (100) substrate exposed to an As ionized cluster beam (ICB) was investigated by means of coaxial impact collision ion scattering spectroscopy (CAICISS). As a result of the measurements, first, it was proven that the Si surface is not damaged by As ICB exposure, although implanted As atoms of several percent were detected in the surface region. Second, both As and Si atoms from double domains of 2×1 and 1×2, and the predominant domain seems to be 2×1. Furthermore, 1×2 domain of As contributes to a lateral contraction of the surface.

It has been found that the exposure of a Si (100) surface to an As ionized cluster beam (ICB) is effective in the preparation of the surface prior to epitaxial growth of GaAs under conventional high vacuum conditions of 2×10−5 Pa. This process is achieved at a temperature as low as 600 °C. A clear 1×2 or 2×2 reflection high energy electron diffraction pattern observed after the procedure indicates good ordering of the sample surface. The cleaning process is attributed to chemical and physical sputtering by As ICB in the first stage and to the subsequent As termination of Si dangling bonds. It has been found that the optimum preparation conditions are an accelerating voltage of the As ionized cluster beam of 1.3 kV and a substrate temperature of 600 °C. GaAs films deposited on As ICB treated Si (100) substrates show good crystal quality with single domain structure.

Cesium bismuth molybdate hydrate was synthesized from bismuth molybdate hydrate and cesium nitrate in aqueous solution, and reversively changed to bismuth molybdate hydrate in nitric acid. Cesium ion in cesium bismuth molybdate hydrate was easily exchanged with potassium, rubidium and ammonium ions while bismuth molybdate hydrate had no reaction except with cesium ion.

Three phases, (Li x Mg 1− x ) 3 N 2− x (0 x x Mg 1− x ) 2 N (2− x )2/3 (0.5 x 3 N – Mg 3 N 2 system at 900 and 1000 K, and their crystal structures were investigated by applying the Rietveld method to the X-ray powder diffraction patterns. (Li x Mg 1− x ) 3 N 2− x crystallizes in a cubic superlattice ( a =9.9767(5) A at x =0.17). Mg atoms in the Mg 3 N 2 structure (space group Ia 3) were found to be partially replaced by Li atoms and the resultant structure was distorted with a lower symmetry space group I213 . The crystal structure of LiMgN (orthorhombic, a =7.1586(2), b =3.5069(8), c =5.01424(13) A, space group Pnma ) was determined ab initio from the X-ray powder diffraction data. It revealed a cation-ordered antifluorite-type structure. (Li x Mg 1− x ) 2 N (2− x )2/3 was prepared by rapid cooling from 1000 K to room temperature. It was also found to be stable at 900 and 1000 K and decomposed into LiMgN and Li 3 N on slow cooling in the furnace. Broad tails of the X-ray diffraction peaks suggest a modulated structure. A cation-disordered simple antifluorite type (space group Fm3m , a =4.99559(11) A at x =0.57) was proposed as the fundamental structure of (Li x Mg 1− x ) 2 N (2− x )2/3 .

Cesium bismuth molybdate hydrate was synthesized from bismuth molybdate hydrate and cesium nitrate in aqueous solution, and reversively changed to bismuth molybdate hydrate in nitric acid. Cesium ion in cesium bismuth molybdate hydrate was easily exchanged with potassium, rubidium and ammonium ions while bismuth molybdate hydrate had no reaction except with cesium ion.

The terminating structure of 6H–SiC(0001) substrates fabricated by the Acheson method was directly identified by means of coaxial impact collision ion scattering spectroscopy (CAICISS). The CAICISS spectra showed that the topmost surfaces of the samples were Si-terminated planes for both the front and rear faces. It was also shown that the (0001)Si face was composed of Si-terminated flat terraces and steps, the height of which corresponded to one-half the unit cell length along the 6H–SiC c axis.

The terminating atomic plane of SrTiO3 (001) surface was investigated by means of coaxial impact‐collision ion scattering spectroscopy (CAICISS). CAICISS spectra proved that SrTiO3 (001) surfaces of as‐supplied substrates as well as of O2‐annealed substrates were predominantly terminated with TiO2 atomic plane, while the SrO atomic plane came at the topmost surface of SrTiO3 (001) homoepitaxial film. This indicates the structural conversion of the topmost atomic layer from TiO2 to SrO occurred during the SrTiO3 homoepitaxial growth. The azimuth rotational CAICISS spectra exhibited a fourfold symmetry in the surface atom alignments, showing the square lattice structure of a terminating plane.

The atomically smooth SrTiO(3) (100) with steps one unit cell in height was obtained by treating the crystal surface with a pH-controlled NH(4)F-HF solution. The homoepitaxy of SrTiO(3) film on the crystal surface proceeds in a perfect layer-by-layer mode as verified by reflection high-energy electron diffraction and atomic force microscopy. Ion scattering spectroscopy revealed that the TiO(2) atomic plane terminated the as-treated clean surface and that the terminating atomic layer could be tuned to the SrO atomic plane by homooepitaxial growth. This technology provides a well-defined substrate surface for atomically regulated epitaxial growth of such perovskite oxide films as YBa(2)Cu(3)O(7-delta).

We have observed the sputtered and the annealed InP [001] surfaces to determine the species of the topmost atomic plane on these surfaces by coaxial impact collision ion scattering spectroscopy (CAICISS). We have identified that the indium top surface without serious roughness can be acquired by Ar/sup +/ sputtering even if the substrate temperature is as low as 300 /spl deg/C. In AFM observations, this surface exhibits textured structure, which is composed of double atomic height steps. Furthermore, the azimuthal dependence of CAICISS spectra show two-fold symmetry with respect to the axis, which indicates that the crystalline quality of this surface is quite high. Therefore, we consider that this surface is applicable to the substrate for heteroepitaxial growth.

We have found undiscovered defects on a 4H-SiC epitaxial layer, the shape of which resembles a scraper in images taken by confocal differential interference contrast optical microscopy. The surface morphological structure and formation mechanism of the scraper-shaped defects were investigated by atomic force microscopy and grazing incidence monochromatic synchrotron X-ray topography, respectively. The scraper-shaped defects were surface morphological defects consisting of surface asperity and were caused by the migration of interfacial dislocations. The evaluation of the thermal oxide reliability of metal–oxide–semiconductor capacitors fabricated on these defects was performed by time-dependent dielectric breakdown measurement. The degradation of thermal oxide occurred only on the downstream line of the scraper-shaped defects. The thickness of the oxide layer on these defects was also investigated using cross-sectional transmission electron microscopy.

The reliability of the gate oxide on large-area surface defects (trapezoid-shaped and obtuse triangular defects) in 4H-SiC epitaxial wafers is discussed. Time-dependent dielectric breakdown measurements revealed that a reduction in charge-to-breakdown (Q bd) occurred at a MOS capacitor including the downstream line of those defects. The deterioration of Q bd was at the same level in trapezoid-shaped defects and obtuse triangular defects. A cross-sectional transmission electron microscope (TEM) image and the simulation of the electric field distribution for the MOS structure indicated that the local fluctuation of the oxide thickness and/or the roughness of the interface on the downstream lines caused the degradation of the reliability of the MOS capacitors.

The topmost atoms of TiO2 - terminated SrTiO3(001) annealed at temperatures between room temperature and 800°C in ultra high vacuum (UHV), have been studied by means of in-situ coaxial impact collision ion scattering spectroscopy (CAICISS). Both time-of-flight spectra at the incident angle of 45.0°C along [ $$\overline{1}$$ 00] azimuth and of 35.3°C along [ $$\overline{1}\overline{1}$$ 0] azimuth revealed Ti and weak O peaks and no Sr peak at 150°C, which means that the topmost layer at 150°C is terminated by TiCh-plane, completely. On the other hand, as increasing the substrate temperature, Sr peak began to appear above 400°C. This Sr peak intensity from both directions was drastically increased with elevating the substrate temperature. This indicates that the topmost O and Ti atoms desorb from the surface at the higher substrate temperature. The ratio Sr/Ti corresponds to the amount of the topmost oxygen or titanium vacancies due to the desorption. It was found that 40 % of the topmost oxygen atoms and 32% of the topmost titanium atoms desorb from TiO2-terminated SrTiO3(001) surface at 800°C. The activation energies for oxygen and titanium desorption were 0.28eV and 0.40eV, respectively.

In situ characterization of the topmost surface of SrTiO3(001) was performed by means of coaxial impact collision ion scattering spectroscopy. As a result, it was proven that the displacement of Sr atoms occurred in the surface region at high temperatures around 500 °C in the case of the as-supplied SrTiO3 substrates terminated with TiO2 atomic plane. Sr atoms shifted by 0.012±0.002 nm toward [001] direction. On the other hand, no displacement was observed in the case of O2 annealed samples at 1000 °C for 10 hours. It indicated that the stable topmost surface structure was formed by the high temperature annealing in the SrTiO3 substrates.

The pridine intercalate of bismuth molybdic acid was prepared from the reaction between dehydrated bismuth molybdic acid and gaseous pyridine. The extent of the pyridine intercalation was 2/3 and the bilayer of pyridinium ion was formed between the oxide sheets. The intercalation reaction with 3- or 4-methylkpridine proceeded similarly to that with pyridine. The pyridine intercalate had the space for the adxorbtion of water while no water was adsorbed on the 4-methylpyridine intercalate because of methl group of hinderance. The intercalate with a monolayer of 4-methylpyridinium ion was obtained by heating the bilayer intercalate at 250°C.

Molecular layer epitaxy and the topmost surface structure in laser MBE of perovskite and other related oxides were investigated by in situ RHEED, in situ angle-resolved XPS (ARXPS) and ex situ co-axial ISS (CAICISS) analyses. Two-dimensional epitaxial growths of SrTiO3 (001) and BaCuO2(001) on SrTiO3(001) substrate were achieved by optimizing the growth conditions. Periodicities of RHEED oscillation corresponded well to the growth of a repeating unit cell (molecular layer). ARXPS and CAICISS spectra revealed that (Sr-0) atomic plane came at the top of SrTiO3(001) film growing on SrTiO3 (001) substrate with (Ti-O) atomic plane on the top. This indicates the structural conversion of the topmost atomic layer from TiO2 to SrO occurred during the SrTiO3 homoepitaxial growth.

Polycrystalline samples La2−x Ba x CuO4+δ(0 ≤ x ≤ 0.145), being prepared by the conventional solid state technique, were electrochemically oxidized at room temperature, and their lattice parameters, electrical resistivities, magnetic susceptibilities, Seebeck coefficients, and gas evolution with increasing temperature were measured. All the electrolyzed samples showed a Tc ≥ 31 K, except for x = 0.125, and possessed almost constant hole concentration p ≈ 0.16 holes/formula unit. The result of TG-Mass-spectrometry showed that the oxidation of copper ions can not be attributed only to the incorporation of excess O2- ions into the lattice.

GaAs epilayers on (100)Si substrates have been grown by ionized cluster beam(ICB) method under conventional high vacuum conditions. The developed deposition method has two characteristics: first is cleaning the Si surface by accelerated As clusters and second is adopting double layer structure in order to confine dislocations within a primary layer. As a result of these features, the etch pit density came to be 2–106cm-2 and the crystal quality was comparable to that of molecular beam epitaxy(MBE) or metal organic chemical vapor deposition(MOCVD) method. In the present paper, we discuss those characteristic phenomena of ICB method and demonstrate MESFET's fabricated on our GaAs grown on Si substrates.

0. Introduction The shift of person categories is not uncommon in the world’s languages. In particular, it is widely observed that third person forms have come to be used as second person forms in some European languages for the purpose of politeness. For example, German uses the third person Sie as a polite second person pronoun. Similarly, Spanish polite second person pronoun usted comes from the nominal form vuestra merced ‘your grace’ which is formally a third person form. The same type of development is suggested for pronouns from other languages, such as Portuguese voce (from Voce Merce ‘your grace’) and Italian lei (from la vostra Signoria ‘your lord’) (Muhlhausler and Harre 1990). A similar situation holds for Asian languages such as Thai, Burmese, and Vietnamese where lexical nous ‘servant’ and ‘lord’ are used for the first and second person, respectively. In Japanese, it is argued that the shift of person categories is not limited to the cross-linguistically common shift from the third to first/second person. The shifts from the first to second person as well as from the second person to first person are reported (Whitman 1999, Shibasaki 2005). Consider the following examples.

Recording marks on a phase-change optical disk were observed by lateral force microscopy (LFM), and the images were compared with those obtained by Kelvin force microscopy (KFM). The spatial resolution of LFM was considerably better than that of KFM. Therefore it is expected that LFM will become one of the effective techniques for evaluating the shapes of recording marks in next-generation phase-change optical disks.

Electron temperature and density of plasma flow, which was obtained from a magneto-plasma-dynamic (MPD) arc jet, were measured by the triple-probe method. In order to apply the MPD arc jet to thin-film processing, the changes in the plasma parameters on a processing substrate were investigated.

Room-temperature (20° C) epitaxy of high-melting point CeO2 thin films was achieved for the first time on Si(111) substrates. Cross-sectional high-resolution transmission electron microscopy, Rutherford backscattering spectrometry and ion scattering spectroscopy confirmed the formation of a sharp oxide/silicon heterointerface with no boundary amorphous layer and single crystallinity of the present CeO2 films. This was achieved by pulsed laser deposition in an ultrahigh vacuum under optimized oxygen partial pressures and by hydrogen termination of the Si surface.

The atomically ultrasmooth surfaces with atomic steps of sapphire substrates were obtained by annealing in air at temperatures between 1000 and 1400 °C. The terrace width and atomic step height of the ultrasmooth surfaces were controlled on an atomic scale by changing the annealing conditions and the crystallographic surface of substrates. The obtained ultrasmooth surface was stable in air. The topmost atomic structure of the terrace was examined quantitatively by atomic force microscopy and ion scattering spectroscopy as well as a theoretical approach using molecular dynamics simulations.

The surface structure of a Si (100) substrate exposed to an As ionized cluster beam (ICB) prior to epitaxial growth of GaAs was investigated by means of coaxial impact collision ion scattering spectroscopy (CAICISS). As a result of the measurement, first, it was proven that both As and Si dimers were formed after As ICB exposure. Second, both As and Si atoms form double domains of 2×1 and 1×2, and both As and Si areas of one domain are larger than those of the other domain in the case of a 3°-off Si substrate. Furthermore, it is likely that As atoms terminate Si atoms as if the As atoms replace the top Si layer. Third, the Si surface is not damaged by As ICB exposure, and the As ions seem to be implanted to the substitutional sites.

The reason why electrical characteristics of GaAs films grown on CaF2/Si(111) structures at high substrate temperature (600°C) are degraded is studied. Rutherford backscattering spectroscopy (RBS) measurements and secondary ion mass spectroscopy (SIMS) observations revealed that the degradation was due to point defects which resulted from a degraded interface region formed by mutual diffusion between GaAs and CaF2. It was found that the 2-step growth method was effective in reducing the point defects of GaAs film.