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Showing papers on "Epitaxy published in 2000"


Journal Article
TL;DR: In this paper, the result of the PtSi nanometer thin film based on silicon prepared by the pulsed laser deposition was described and the physical principle, unique characteristics and the proceeding of the study were introduced briefly.
Abstract: The pulsed laser deposition is a new technique for the growth of thin films,which has been attended generally by people recently The physical principle, unique characteristics and the proceeding of the study were introduced briefly In addation, the result of the PtSi nanometer thin film based on silicon prepared by the pulsed laser deposition was describedPULS

392 citations


Journal ArticleDOI
TL;DR: In this paper, a new class of half-metallic ferromagnets has been found in the zinc-blende crystal structure by ab initio calculations based on the local spin-density approximation.
Abstract: A new class of half-metallic ferromagnets has been found in the zinc-blende crystal structure. The previously nonexistent zinc-blende CrAs thin films have been synthesized on GaAs (001) substrates by molecular-beam epitaxy, and show a ferromagnetic behavior at room temperature. The zinc-blende CrAs has been designed by ab initio calculations based on the local spin-density approximation, and the calculation predicts the highly spin-polarized electronic band structure.

385 citations


Journal ArticleDOI
TL;DR: In this article, high-quality zinc oxide (ZnO) films were epitaxially grown on R-plane sapphire substrates by metalorganic chemical vapor deposition at temperatures in the range of 350°C to 600°C.
Abstract: High-quality zinc oxide (ZnO) films were epitaxially grown on R-plane sapphire substrates by metalorganic chemical vapor deposition at temperatures in the range of 350°C to 600°C. In-situ nitrogen compensation doping was performed using NH3. Microstructural and optical properties of the films, as well as the N-doping effects, were studied. The metal-semiconductor-metal ultraviolet sensitive photodetectors were fabricated on N-doped epitaxial ZnO films. The detector showed fast photoresponse, with a rise time of 1 µs and a fall time of 1.5 µs. Low-frequency photoresponsivity, on the order of 400 A/W at 5 V bias, was obtained.

357 citations


Journal ArticleDOI
TL;DR: In this article, the results concerning the electrodeposition of zinc oxide layers by reduction of dissolved oxygen in the presence of Zn(II) ions are presented, and a concomitant variation of the photoluminescence emission in the blue is observed.

299 citations


Journal ArticleDOI
TL;DR: In this paper, the growth and characterization of both epitaxial and amorphous films Gd2O3 of (e=14) and Y2O-3(e=18) as the gate dielectrics for Si prepared by ultrahigh vacuum vapor deposition was reported.
Abstract: We report on growth and characterization of both epitaxial and amorphous films Gd2O3 of (e=14) and Y2O3(e=18) as the gate dielectrics for Si prepared by ultrahigh vacuum vapor deposition. The use of vicinal Si (100) substrates is key to the growth of (110) oriented, single-domain films in the Mn2O3 structure. Typical electrical leakage results are 10−3 A/cm2 at 1 V for single domain epitaxial Gd2O3 and Y2O3 films with an equivalent SiO2 thickness, teq of 15 A, and 10−6 A/cm2 at 1 V for smooth amorphous Y2O3 films (e=18) with a teq of only 10 A. For all the Gd2O3 films, the absence of SiO2 segregation at the interface is established from infrared absorption measurements.

293 citations


Journal ArticleDOI
TL;DR: A modified droplet epitaxy method for fabricating self-organized GaAs/AlGaAs quantum dots (QDs) with a high As flux irradiation and a low substrate temperature was proposed in this paper.
Abstract: We propose a modified droplet epitaxy method for fabricating self-organized GaAs/AlGaAs quantum dots (QDs) with a high As flux irradiation and a low substrate temperature. By our novel method, GaAs QDs were successfully formed, retaining their pyramidal shape, original base size and density of droplets, and preventing layer-by-layer growth. Quantum size effects of the QDs were distinctly observed by photoluminescence measurements. It was confirmed that this new modified droplet epitaxy method is promising for fabricating a high-quality GaAs/AlGaAs QD system.

259 citations


Journal ArticleDOI
TL;DR: In this paper, high electrically conductive indium-tin-oxide thin films were epitaxially grown on an extremely flat (100) surface of yttria-stabilized zirconia single-crystal substrates at a substrate temperature of 600 °C by a pulsed-laser deposition technique.
Abstract: Highly electrically conductive indium–tin–oxide thin films were epitaxially grown on an extremely flat (100) surface of yttria-stabilized zirconia single-crystal substrates at a substrate temperature of 600 °C by a pulsed-laser deposition technique. A resistivity down to 7.7×10−5 Ω cm was reproducibly obtained, maintaining optical transmission exceeding 85% at wavelengths from 340 to 780 nm. The carrier densities of the films were enhanced up to 1.9×1021 cm−3, while the Hall mobility showed a slight, almost linear, decrease from 55 to 40 cm2 V−1 s−1 with increasing SnO2 concentration. The low resistivity is most likely the result of the good crystal quality of the films.

259 citations


Journal ArticleDOI
TL;DR: In this article, migration-enhanced epitaxy was used to study the growth of InN on sapphire with an AlN buffer layer, which is composed of an alternative supply of pure In atoms and N2 plasma.
Abstract: Epitaxial growth of InN on (0001) sapphire with an AlN buffer layer was studied by migration-enhanced epitaxy, which is composed of an alternative supply of pure In atoms and N2 plasma. A series of samples were prepared with different substrate temperatures ranging from 360 to 590 °C. As-grown films were characterized by x-ray diffraction (XRD), reflective high-energy electron diffraction, atomic-force microscopy (AFM), and Hall measurements. Both XRD θ–2θ and ω scans show that the full width at half maximum of the (0002) peak nearly continuously decrease with increasing growth temperature, while InN grown at 590 °C shows the poorest surface morphology from AFM. It is suggested that three-dimensional characterization is necessary for an accurate evaluation of the quality of the InN epilayer. Hall mobility as high as 542 cm2/V s was achieved on film grown at ∼500 °C with an electron concentration of 3×1018 cm−3 at room temperature. These results argue against the common view that nitrogen vacancies are res...

207 citations


Journal ArticleDOI
TL;DR: In this paper, the growth and characterization of zinc-blende ZnO on GaAs(001) substrates was reported, which showed bright band-edge luminescence at room temperature.
Abstract: A stable wurtzite phase of ZnO is commonly observed. In this letter, we report the growth and characterization of zinc-blende ZnO on GaAs(001) substrates. The ZnO films grown on GaAs(001) substrates using microwave-plasma-assisted metalorganic molecular-beam epitaxy were characterized by reflection high-energy electron diffraction, x-ray diffraction, transmission electron microscope, and atomic force microscope measurements. The use of a ZnS buffer layer was found to lead to the growth of the zinc-blende ZnO films. Although the zinc-blende ZnO films were polycrystalline with columnar structures, they showed bright band-edge luminescence at room temperature.

196 citations


Journal ArticleDOI
TL;DR: In this article, a cantilever epitaxy (CE) method was used to reduce threading dislocations in GaN grown directly on flat sapphire substrates.
Abstract: The density of threading dislocations (TD) in GaN grown directly on flat sapphire substrates is typically greater than 10{sup 9}/cm{sup 2}. Such high dislocation densities degrade both the electronic and photonic properties of the material. The density of dislocations can be decreased by orders of magnitude using cantilever epitaxy (CE), which employs prepatterned sapphire substrates to provide reduced-dimension mesa regions for nucleation and etched trenches between them for suspended lateral growth of GaN or AlGaN. The substrate is prepatterned with narrow lines and etched to a depth that permits coalescence of laterally growing III-N nucleated on the mesa surfaces before vertical growth fills the etched trench. Low dislocation densities typical of epitaxial lateral overgrowth (ELO) are obtained in the cantilever regions and the TD density is also reduced up to 1 micrometer from the edge of the support regions.

186 citations


Journal ArticleDOI
TL;DR: In this article, the piezoelectric coefficient d33 of gallium nitride (GaN) thin films grown on silicon substrates by molecular beam epitaxy have been measured using a laser interferometer.
Abstract: The piezoelectric coefficient d33 of aluminum nitride (AlN) and gallium nitride (GaN) thin films grown on silicon substrates by molecular beam epitaxy have been measured using a laser interferometer. X-ray diffraction reveals that the AlN and GaN films consist mainly of crystals with a hexagonal wurtzite structure. In order to grow epitaxial GaN films, an AlN film was first deposited on silicon as the buffer layer, so the d33 measurement for GaN was actually performed on GaN/AlN/Si multilayer systems. The relative permittivity and electrical resistivity of each constituent layer of the film and the potential drop across each layer were determined as a function of frequency. The potential drops were then used to calculate the piezoelectric coefficient d33 of GaN. After correcting for substrate clamping, d33 of AlN and GaN were found to be (5.1±0.1) and (3.1±0.1) pm V−1, respectively.

Journal ArticleDOI
TL;DR: In this paper, room temperature electroluminescence (EL) was obtained for the first time from a Si-based light emitting diode with semiconducting silicide (β-FeSi2) active region.
Abstract: Room temperature electroluminescence (EL) was obtained for the first time from a Si-based light emitting diode with semiconducting silicide (β-FeSi2) active region. The peak wavelength was 1.6 µm and it is from β-FeSi2 balls embedded in a Si p-n junction. An a-axis oriented β-FeSi2 layer was grown on n+-(001) Si by reaction deposition epitaxy (RDE), then p- and p+-Si layers were grown by molecular beam epitaxy (MBE). The β-FeSi2 aggregated into balls with about 100 nm diameter in this process. The EL intensity increased superlinearly with increase of the injected current density, and reasonable EL was obtained at current density above 10 A/cm2, though the photoluminescence (PL) was difficult to be detected at room temperature.

Journal ArticleDOI
TL;DR: In this paper, high-resolution x-ray diffraction measurements show an increase in lateral coherence length from several tens of nanometers to > 0.7μm for growth of c-oriented ZnO on the a surface as opposed to the c surface of sapphire.
Abstract: High-quality, c-oriented ZnO epitaxial films have been grown on the a surface using molecular-beam epitaxy. The use of a-oriented sapphire eliminates rotational domains and related structural defects which have limited the use of ZnO in electronic applications. The ZnO epitaxial layers are uniquely oriented with the ZnO/sapphire orientational relationship [0001]‖[1120] and 〈1120〉‖[0001]. This unique orientation is a consequence of the anisotropy of the a-sapphire surface in conjunction with a strong correlation along a single direction leading to the term uniaxial locked epitaxy. High-resolution x-ray diffraction measurements show an increase in x-ray lateral coherence length from several tens of nanometers to >0.7 μm for growth of c-oriented ZnO on the a surface as opposed to the c surface of sapphire.

Journal ArticleDOI
TL;DR: In this article, thin gallium nitride films 250-350 µm in thickness were grown on 2-inch-diameter sapphire wafers by hydride vapor phase epitaxy.
Abstract: Thick gallium nitride films 250–350 µm in thickness were grown on 2-inch-diameter (0001) sapphire wafers by hydride vapor phase epitaxy. The size of the free-standing GaN substrates without cracks separated from the sapphire substrates by laser processing was equal to that of the initial sapphire substrates. The origin of bowing and the broad photoluminescence (PL) spectra of GaN films was considered the difference in the residual strain between the front and bottom surfaces caused by threading dislocations.

Journal ArticleDOI
TL;DR: The dependence of polar direction of GaN film on growth conditions has been investigated by changing either the group-V/group-III ratio (V/III ratio) in supplying the source gas or the deposition rate as mentioned in this paper.
Abstract: The dependence of polar direction of GaN film on growth conditions has been investigated by changing either the group-V/group-III ratio (V/III ratio) in supplying the source gas or the deposition rate. GaN films were deposited on a nitrided sapphire by two-step metalorganic chemical vapor deposition. The surface morphology changed from flat hexagonal to pyramidal hexagonal facet with the increase of V/III ratio. However, the polar direction of GaN on an optimized buffer layer of 20 nm thickness was N-face (−c) polarity, independent of both the V/III ratio and the deposition rate. The polarity of the GaN epitaxtial layer can be determined by that of an interface (nitrided sapphire, annealed buffer layer or GaN substrate) at the deposition of GaN epitaxial layer. The higher V/III ratio enhanced the nucleation density, and reduced the size of hexagonal facets. The nuclei, forming the favorable hexagonal facets of wurtzite GaN, should grow laterally along the {1010} directions to cover a room among the facet...

Journal ArticleDOI
TL;DR: In this paper, the growth and transport properties of high-mobility two-dimensional electron gases (2DEGs) confined at the AlGaN/GaN interface grown by plasma-assisted molecular-beam epitaxy on GaN templates prepared by hydride vapor phase epitaxy were investigated.
Abstract: We report on the growth and transport properties of high-mobility two-dimensional electron gases (2DEGs) confined at the AlGaN/GaN interface grown by plasma-assisted molecular-beam epitaxy on GaN templates prepared by hydride vapor phase epitaxy. We have grown samples over a broad range of electron densities ranging from ns=6.9×1011 to 1.1×1013 cm−2, and at T=4.2 K, observe a peak mobility of 53 300 cm2/V s at a density of 2.8×1012 cm−2. Magnetotransport studies on these samples display exceptionally clean signatures of the quantum Hall effect. Our investigation of the dependence of 2DEG mobility on carrier concentration suggests that the low-temperature mobility in our AlGaN/GaN heterostructures is currently limited by the interplay between charged dislocation scattering and interface roughness.

Patent
27 Jan 2000
TL;DR: In this paper, a multilayered structure with a single crystal film (12) bonded to a polycrystalline substrate (10) has been constructed by growing an epitaxial layer (14, 14') on said single-crystal film.
Abstract: A method for making a multilayered structure with a single crystal film (12) bonded to a polycrystalline substrate (10) has the steps of bonding a single crystal film to a polycrystalline substrate, and growing an epitaxial layer (14, 14') on said single crystal film bonded to said polycrystalline substrate.

Journal ArticleDOI
TL;DR: In this paper, the optical properties of epitaxial ZnO layers were studied in the spectral region from 1.5 to 5.4 eV using four-zone null spectroscopic ellipsometry.
Abstract: Optical properties of epitaxial ZnO layers have been studied in the spectral region from 1.5 to 5.4 eV using four-zone null spectroscopic ellipsometry. An existing model dielectric function based on excitonic structure near direct band gap has been improved by including a high-energy absorption term. Surface layer, corresponding to the surface roughness, was found to be essential to fit the spectroellipsometric data obtained. Two kinds of samples have been studied: ZnO layers prepared on (0001) and (1120)-oriented sapphire substrates. The surfaces of the first ones were found to be more rough.

Journal ArticleDOI
TL;DR: In this paper, the lattice deformation of dense strained La0.7Sr0.3MnO3 (LSMO) films is shown to control the easy direction of the magnetization.
Abstract: The lattice deformation of dense strained La0.7Sr0.3MnO3 (LSMO) films is shown to control the easy direction of the magnetization. Optimized pulsed laser deposited conditions allow the fabrication of dense LSMO thin films which present an exceptional flatness with a peak–valley roughness (Rp–v) of 1 A, associated to epitaxial grains as large as 1 μm. Electron microscopy coupled with x-ray diffraction have been used to study the unit cell distortion of both tensile and compressive dense LSMO films as a function of the thickness. No relaxation of the lattice distortion imposed by substrate has been observed in the thickness range 10–60 nm. The Curie temperature is not significantly affected by the nature of the substrate: a TC of 350 K is observed for both SrTiO3 (STO) and LaAlO3 (LAO) substrates, i.e., close to the bulk material (369 K). In contrast, the easy direction of magnetization depends on the substrate. For tensile films deposited on the STO substrate, the unit cell is elongated along the film’s pl...

Journal ArticleDOI
TL;DR: It is argued that the segregation seed, which decreases from 2 / 3 to 1 / 2 monolayer when growth conditions are made less anion rich, has its origin in the Sb-bilayer reconstruction maintained during GaInSb epitaxy.
Abstract: We show how cross-sectional scanning tunneling microscopy may be used to reconstruct the Sb segregation profiles in GaInSb $/$InAs strained-layer superlattices. These profiles are accurately described by a one-dimensional model parametrizing the spatial evolution of an Sb seed at the InAs-on-GaInSb interface in terms of two-anion-layer exchange. We argue that the segregation seed, which decreases from $\frac{2}{3}$ to $\frac{1}{2}$ monolayer when growth conditions are made less anion rich, has its origin in the Sb-bilayer reconstruction maintained during GaInSb epitaxy.

Journal ArticleDOI
TL;DR: In this article, a new preparation was reported which, for the first time, results in a thin, crystalline SiO2 film on a Mo(112) single crystal.
Abstract: A new preparation is reported which, for the first time, results in a thin, crystalline SiO2 film on a Mo(112) single crystal. The procedure consists of repeated cycles of silicon deposition and subsequent oxidation, followed by a final annealing procedure. AES and XPS have been used to control film stoichiometry. LEED pictures of high contrast show a hexagonal, crystalline SiO2 overlayer with a commensurate relationship to the Mo(112) substrate. The wetting of the substrate by the film has been investigated by LEED, XPS and TDS, revealing that the film covers the substrate completely.

Journal ArticleDOI
TL;DR: In this paper, the optical and structural properties of high-quality ZnO films grown on epitaxial GaN (epi-GaN) by plasma-assisted molecular-beam epitaxy employing low-temperature buffer layers were investigated.
Abstract: We have investigated the optical and structural properties of high-quality ZnO films grown on epitaxial GaN (epi-GaN) by plasma-assisted molecular-beam epitaxy employing low-temperature buffer layers. High-resolution x-ray diffraction for both symmetric and asymmetric reflexes shows that crystalline defects in ZnO films have a similarity to epi-GaN used as a substrate. The quality of ZnO epilayers grown on epi-GaN is basically determined by epi-GaN. The photoluminescence (PL) spectrum at 10 K exhibits very sharp exciton emission with a linewidth of 1.5 meV, while deep-level emission is negligible, indicative of small residual strain. At 77 K, PL is dominated by a free-exciton emission line in the low-excitation regime, while it is overtaken by a new emission band due to biexcitons at its low-energy side as the excitation intensity increases. This biexciton emission band emerges even under the intermediate excitation regime of 100 W/cm2, which is 100 times smaller than the previously reported threshold for...

Journal ArticleDOI
TL;DR: In this article, the amount of incorporated Mg atoms changes approximately linearly with incident Mg flux, and the hole mobility depends strongly on the hole concentration, varying from μp=24.8×1017 cm2/V
Abstract: GaN:Mg layers grown by plasma-assisted molecular-beam epitaxy at 650 °C are investigated. Secondary-ion-mass-spectroscopy measurements reveal uniform Mg doping profiles with very sharp boundaries. The amount of incorporated Mg atoms changes approximately linearly with incident Mg flux. Hall measurements on p-type GaN:Mg layers show that about 1%–2% of all Mg atoms are ionized at room temperature. The hole mobility depends strongly on the hole concentration, varying from μp=24 cm2/V s for p=1.8×1017 cm−3 to μp=7.5 cm2/V s for p=1.4×1018 cm−3. GaN p–n diodes with molecular-beam-epitaxy-grown p regions are analyzed using current–voltage measurements.

Journal ArticleDOI
TL;DR: In this article, an air-bridged lateral epitaxial overgrowth technique was used to reduce the wing tilt and threading dislocation density in GaN thin films, and the density of dislocations in the wing region was reduced to be <107 cm−2, which was at least two orders of magnitude lower than that of underlying GaN.
Abstract: A promising technique of selective lateral epitaxy, namely air-bridged lateral epitaxial overgrowth, is demonstrated in order to reduce the wing tilt as well as the threading dislocation density in GaN thin films. A seed GaN layer was etched to make ridge-stripe along 〈1100〉GaN direction and a GaN material was regrown from the exposed (0001) top facet of the ridged GaN seed structures, whose sidewalls and etched bottoms were covered with silicon nitride mask, using low-pressure metalorganic vapor phase epitaxy. The density of dislocations in the wing region was reduced to be <107 cm−2, which was at least two orders of magnitude lower than that of underlying GaN. The magnitude of the wing tilt was determined to be 0.08° by x-ray diffraction (XRD) measurements, which was smaller than other lateral epitaxial overgrown GaN thin films. The full width at half maximum of XRD for the wing region was 138 arc sec, indicating high uniformity of c-axis orientation.

Journal ArticleDOI
07 Jan 2000-Science
TL;DR: A mechanism for the heteroepitaxial growth of diamond is suggested, in which etching of the nondiamond carbon binder exposes and removes nonadherent nanodiamond nuclei, leaving intact only those directly nucleated on the silicon substrate.
Abstract: A diamond nucleation site responsible for epitaxial growth of diamond on silicon by chemical vapor deposition (CVD) is identified in high-resolution transmission electron microscopic images. Other sites in the same sample leading to polycrystalline growth, but deleterious to epitaxial CVD growth, are also described. A mechanism for the heteroepitaxial growth of diamond is suggested, in which etching of the nondiamond carbon binder exposes and removes nonadherent nanodiamond nuclei, leaving intact only those directly nucleated on the silicon substrate. This work enhances our understanding of diamond nucleation and heteroepitaxial growth and its potential applications.

Journal ArticleDOI
TL;DR: The defect structure of strontium titanate thin films epitaxially grown on SrTiO3(100) substrates by pulsed-laser deposition was studied using transmission electron microscopy and X-ray diffraction as mentioned in this paper.
Abstract: The defect structure of non-stoichiometric strontium titanate thin films epitaxially grown on SrTiO3(100) substrates by pulsed-laser deposition was studied using transmission electron microscopy and X-ray diffraction. The A-site-excess SrTiO3 thin film adopted a completely unrelaxed pseudomorphic perovskite structure with an enlarged lattice parameter normal to the surface. Excess SrO was accommodated as Ruddlesden-Popper planar faults showing a peculiar three-dimensional mosaic structure, without forming secondary phases or dislocations due to non-stoichiometry. Biaxial compressive stress induced by lattice mismatch between the film and substrate was estimated at 9,7 GPa. Such a highly strained film is attributable to planar fault formation, which increases the cell volume and suppresses misfit dislocations. The B-site-excess SrTiO3 thin-film microstructure consisted of crystalline SrTiO3 and amorphous TiO2-rich phases. The slight increase in the lattice parameter normal to the surface and cryst...

Journal ArticleDOI
K Haga, M Kamidaira, Y Kashiwaba, Takashi Sekiguchi1, H. Watanabe 
TL;DR: In this paper, high quality ZnO films were successfully prepared by a remote plasma-enhanced CVD of Zn(C 2 H 5 ) 2 and carbon dioxide.

Journal ArticleDOI
TL;DR: In this paper, a transmission electron microscopy study of structural defects induced by the introduction of Mg during the growth of metalorganic vapor phase epitaxy GaN is presented, where the defects are assumed to be pyramidal inversion domains with an hexagonal base and {1123} inclined facets.
Abstract: A transmission electron microscopy study of structural defects induced by the introduction of Mg during the growth of metalorganic vapor phase epitaxy GaN is presented. These defects are assumed to be pyramidal inversion domains with an hexagonal base and {1123} inclined facets. The tip of the pyramids is always pointing toward the [0001] direction, i.e., in a Ga-terminated film, toward the substrate and in a N-terminated film, toward the surface. A chemical quantitative analysis shows that these pyramidal defects are Mg rich. They are present in all the studied films, independent of the doping level.

Journal ArticleDOI
TL;DR: In this article, the growth mode of homoepitaxial SrTiO3 thin films was mapped as a function of deposition rate and substrate temperature during pulsed laser deposition.
Abstract: We have mapped the growth mode of homoepitaxial SrTiO3 thin films as a function of deposition rate and substrate temperature during pulsed laser deposition. The transition from layer by layer growth to step flow growth was mapped by making 260 depositions, 3 monolayers each, on a single substrate. The growth mode was determined by time-resolved reflection high-energy electron diffraction. An atomically smooth surface was regenerated after each deposition by annealing the sample at temperatures above 1200 °C. The depositions were performed at an oxygen pressure of 10−6 Torr and covered a temperature range from 900 to 1380 °C. The effective activation energies of surface migration on Ti- and Sr-terminated surfaces were determined from the mapping results.

Journal ArticleDOI
TL;DR: In this paper, a series of BaTiO3 thin films with various thicknesses from 10 to 400 nm were epitaxially grown under various oxygen pressures from 2×10−4 to 12 Pa on Sr TiO3 (001) substrates using laser molecular beam epitaxy.
Abstract: A series of BaTiO3 thin films with various thicknesses from 10 to 400 nm were epitaxially grown under various oxygen pressures from 2×10−4 to 12 Pa on SrTiO3 (001) substrates using laser molecular beam epitaxy. Being confirmed by reflection high energy electron diffraction, atomic force microscopy, x-ray diffraction, and high resolution transmission electron microscopy the epitaxial single crystal BaTiO3 thin films are highly c-axis or a-axis oriented with a root-mean-square surface roughness of 0.14 nm. The observed thickness and oxygen pressure dependent structural characteristics of the BaTiO3 thin films are discussed by taking into account both the misfits in thermal expansion and lattice constants between BaTiO3 films and SrTiO3 substrates, and the effect of the energy of the sputtered particles, which is consistent with the established strain relaxation mechanism. An abnormal expansion of lattice volume of a BaTiO3 unit cell is found and attributed to the effect of oxygen vacancies in the BaTiO3 films.