Showing papers on "Epitaxy published in 1992"

Single-Crystal Epitaxial Thin Films of the Isotropic Metallic Oxides Sr1–xCaxRuO3 (0 ≤ x ≤ 1)

Abstract: Single-crystal epitaxial thin films of the isotropic metallic oxides Sr1–xCaxRuO3 (0 ≤ x ≤ 1) were grown on miscut SrTiO3(100) substrates in situ by 90° off-axis sputtering. These thin films exhibit low isotropic resistivities, excellent chemical and thermal stability, good surface smoothness, and high crystalline quality. Furthermore, the lattice parameters and magnetic properties can be varied by simply changing the strontium/calcium ratio. These epitaxial thin films, and their multilayer structures with other oxide materials, can be used for the fabrication of superconducting, ferroelectric, magneto-optic, and electro-optic devices.

Optoelectronic measurement of semiconductor surfaces and interfaces with femtosecond optics

Abstract: The basic concepts and preliminary applications of optically induced electromagnetic radiation from semiconductor surfaces and interfaces by using femtosecond optics are discussed. This submillimeter‐wave radiation provides a novel optoelectronic technique to study semiconductor electronic surface and interface properties with a contactless approach. The amplitude and phase of the electromagnetic radiation from the semiconductor surfaces depend on carrier mobility, impurity doping concentration, and strength and polarity of the static internal field. A large selection of bulk, epitaxial layer and superlattice samples from III‐V, II‐VI and group‐IV semiconductors has been tested. The orientation and strength of the static built‐in fields of a wide range of semiconductor surfaces, such as surface depletion, metal/semiconductor Schottky, p‐n junction and strain‐induced piezoelectric fields, can be determined and estimated.

Ultrafast carrier dynamics in III-V semiconductors grown by molecular-beam epitaxy at very low substrate temperatures

Abstract: Ultrashort carrier lifetimes were experimentally observed in a variety of As-based III-V crystalline semiconductor layers grown by molecular beam epitaxy over a range of very low substrate temperatures. Time-resolved optical absorption, reflection, and photoconductive switching measurements with femtosecond resolution have been used to directly measure the ultrafast carrier dynamics in these materials. GaAs and In/sub 0.52/Al/sub 0.48/As grown at temperatures of 200 and 150 degrees C, respectively, exhibited subpicosecond carrier lifetimes, while lattice-mismatched In/sub x/Ga/sub 1-x/As on GaAs displayed a 7-ps carrier lifetime in material grown at 200 degrees C. A distinct decrease in carrier lifetime with decreasing growth temperature is documented for all three material systems. For epilayers annealed at high-temperature, resistivities are high, and thus these materials were found to be ideally suited for a number of ultrafast optoelectronic applications. A number of applications are reviewed and discussed. >

Epitaxial growth and characterization of zinc‐blende gallium nitride on (001) silicon

Abstract: GaN films have been epitaxially grown onto (001) Si by electron cyclotron resonance microwave‐plasma‐assisted molecular‐beam epitaxy, using a two‐step growth process, in which a GaN buffer is grown at relatively low temperatures and the rest of the film is grown at higher temperatures. This method of film growth was shown to lead to good single‐crystalline β‐GaN and to promote lateral growth resulting in smooth surface morphology. The full width at half‐maximum of the x‐ray rocking curve in the best case was found to be 60 min. Optical‐absorption measurements indicate that the band gap of β‐GaN is 3.2 eV and the index of the refraction below the absorption edge is 2.5. Conductivity measurements indicate that the films may have a carrier concentration below 1017 cm−3.

Surfactant-induced layer-by-layer growth of Ag on Ag(111)

Abstract: We have investigated the epitaxial growth of Ag(111) by x-ray reflectivity experiments. In the temperature range from 175 to 575 K the growth mode changes gradually from three-dimensional to step flow, but at no temperature was layer-by-layer growth observed. Submonolayer deposits of Sb on the starting surface dramatically alter the growth behavior. With Sb the Ag grows layer by layer over the entire temperature range investigated (225--375 K), resulting in smoother surfaces at the lowest growth temperatures. We propose that Sb decreases the barrier for interlayer diffusion.

The influence of oxygen on the electrical and optical properties of GaN crystals grown by metalorganic vapor phase epitaxy

Abstract: Oxygen was observed to influence the electrical and optical properties of GaN layers grown by metalorganic vapor phase epitaxy. The carrier concentrations obtained from Van der Pauw–Hall measurements increased an order of magnitude when oxygen was incorporated into the grown layers. Additionally, the presence of oxygen in the GaN layers also changed the compensation behavior of Zn. Anomalous behavior of optical transitions in the oxygen‐doped GaN layers was observed by optical absorption spectroscopy and low‐temperature (4.2 K) photoluminescence measurements. These properties were studied as a function of growth parameters including growth temperature, amount of doping, etc. A model based on impurity band formation is proposed to explain these experimental results, and it is concluded that oxygen is a ‘‘shallow’’ deep donor in GaN.

Epitaxial growth of TiN films on (100) silicon substrates by laser physical vapor deposition

Abstract: We report epitaxial growth of TiN films having low resistivity on (100) silicon substrates using pulsed laser deposition method. The TiN films were characterized using x‐ray diffraction, Rutherford backscattering, four‐point‐probe ac resistivity, high resolution transmission electron microscopy and scanning electron microscopy techniques and epitaxial relationship was found to be 〈100〉 TiN ∥ 〈100〉 Si. TiN films showed 10%–20% channeling yield. In the plane, four unit cells of TiN match with three unit cells of silicon with less than 4.0% misfit. This domain matching epitaxy provides a new mechanism of epitaxial growth in systems with large lattice misfits. Four‐point‐probe measurements show characteristic metallic behavior of these films as a function of temperature with a typical resistivity of about 15 μΩ cm at room temperature. Implications of low‐resistivity epitaxial TiN in silicon device fabrication are discussed.

Method of producing semiconductor substrate

Abstract: A method of producing a semiconductor substrate, which comprises forming a monocrystalline silicon layer on a porous silicon substrate by epitaxial growth and applying an oxidation treatment to the porous silicon substrate and the monocrystalline silicon layer at least near the interface between the porous silicon substrate and the monocrystalline silicon layer.

In situ transmission electron microscopy studies of silicide‐mediated crystallization of amorphous silicon

Abstract: The silicide‐mediated phase transformation of amorphous to crystalline silicon was observed in situ in the transmission electron microscope. Crystallization of nickel‐implanted amorphous silicon occurred at ∼500 °C. Nickel disilicide precipitates were observed to migrate through an amorphous Si film leaving a trail of crystalline Si. Growth occurred parallel to 〈111〉 directions. High resolution electron microscopy revealed an epitaxial NiSi2/Si(111) interface which was Type A. A diffusion‐controlled mechanism for the enhanced crystallization rate was determined.

GaAs p‐n junction formed in quantum wire crystals

Abstract: A p‐n junction is formed for the first time in a cross‐sectional area of a GaAs wire crystal with a diameter of about 100 nm. Ultrafine cylindrical growth by metalorganic vapor phase epitaxy is employed for the fabrication. Current‐voltage and capacitance‐voltage characteristics confirm the formation of the p‐n junction in a narrow area at the midpoint of a wire crystal. Intensive light emission by current injection is observed at 77 K and even at room temperature. These results suggest that ultrafine optoelectronic devices with quantum‐size p‐n junction are possible.

Hydride vapor phase epitaxial growth of a high quality GaN film using a ZnO buffer layer

Abstract: In hydride vapor phase epitaxial (HVPE) growth of GaN, the sputtered ZnO layer has been found to be one of the best buffer layers because of the fact that physical properties of ZnO are nearly analogous with those of GaN. With a ZnO buffer layer, the reproducibility of growing GaN single crystal by HVPE has been greatly improved. The GaN films grown by this method show excellent crystalline, electrical, and optical properties. In particular, the Hall mobility of 1920 cm2 V−1 s−1 at 120 K is the highest value that has ever been reported by HVPE.

Off-axis laser deposition of YBa2Cu3O7-δ thin films

Abstract: We report on YBa2Cu3O7−δ thin‐film preparation by a new laser deposition geometry, the so‐called off‐axis laser deposition. Combined with radiation‐based substrate heating, this results in c‐axis oriented, epitaxial YBa2Cu3O7−δ thin films with critical current densities above 106 A/cm2 at 77 K and zero field and an exceptionally good surface quality, with complete absence of the otherwise observed laser droplets. As proved by atomic force microscopy, the surface roughness is <80 A over an area of at least 10×10 μm2. Using this off‐axis geometry it is possible to coat both sides of a substrate simultaneously, providing a one‐step process in double‐sided thin‐film deposition. Both YBa2Cu3O7−δ films on the substrate show identical superconducting properties.

Vapor phase epitaxial growth apparatus

Abstract: A vapor phase growth apparatus is disclosed, which comprises a boat accommodating therein a plurality of semiconductor substrates, an inner tube surrounding the boat, an outer tube disposed outside the inner tube, a heater disposed outside the outer tube, a reaction gas injection nozzle disposed inside the inner tube and operating to eject a reaction gas against the semiconductor substrates, and a hydrogen halide gas injection nozzle disposed between the inner tube and the outer tube and operating to inject the hydrogen halide gas, wherein exhaust openings for exhausting the reaction gas are formed through a wall of the inner tube, thereby suppressing deposition of a reactant on an outer surface of the inner tube and an inner surface of the outer tube. The reaction gas injected from the reaction gas injection nozzle flows in the portion formed between the inner tube and the outer tube along with in the inner tube. Since the portion between the inner tube and the outer tube is heated by the heater disposed outside the outer tube, a reactant tends to be deposited on the outer surface of the inner tube and the inner surface of the outer tube. By injecting the hydrogen halide gas from the hydrogen halide gas injection nozzle to the portion formed between the inner tube and the outer tube, the deposition of the reactant can be suppressed.

Misfit dislocations in lattice-mismatched epitaxial films

Abstract: This article reviews current experimental and theoretical knowledge of the relaxation of lattice-mismatch strain via misfit dislocations in heteroepitaxial semiconductor films. The energetics and kinetics of misfit dislocation nucleation, propagation, and interaction processes are described in detail. In addition, there is a brief review of the principal properties of dislocations in bulk semiconductors and an outline of existing models for strained layer stability.

Single‐crystalline, epitaxial cubic SiC films grown on (100) Si at 750 °C by chemical vapor deposition

Abstract: Single‐crystalline, epitaxial cubic (100) SiC films have been grown on (100) Si substrates at 750 °C by low‐pressure chemical vapor deposition, using methylsilane, SiCH3H3, a single precursor with a Si:C ratio of 1:1, and H2. This epitaxial growth temperature is the lowest reported to date. The films were characterized by means of transmission electron microscopy, x‐ray diffraction, infrared transmission, four‐point probe and other methods. Based on double‐crystal x‐ray diffractometry, the crystalline quality of our films is equivalent to that of commercial films of similar thickness. The letter describes the novel growth apparatus used and the properties of the films.

Crystal Structure Change of GaAs and InAs Whiskers from Zinc-Blende to Wurtzite Type

Abstract: Crystal structures of GaAs and InAs whiskers grown by metalorganic vapor phase epitaxy are evaluated by means of a transmission electron microscope. The whiskers are grown epitaxially on GaAs substrates with diameters of 20-100 nm and lengths of 1-5 µm. They have the following characteristics. 1) GaAs whiskers have layered structures with 2-30 nm period, that are the 111 rotating twins of the zinc-blende type. 2) InAs whiskers also have layered structures which consist of wurtzite and zinc-blende type crystals. The wurtzite type InAs is observed for the first time in this study. The volume ratio of these two types strongly depends on the growth conditions, such as substrate temperature and material gas pressure. This suggests that defect-free whiskers with a single phase that are useful for quantum wire devices can be grown by controlling the growth conditions.

Structural and electronic properties of metastable epitaxial FeSi1+x films on Si(111).

Abstract: We have investigated the epitaxial growth and the electronic properties of a metallic metastable FeSi phase crystallizing with the CsCl structure on Si(111) Upon annealing below 500 \ifmmode^\circ\else\textdegree\fi{}C the stoichiometry of thin films (20 \AA{}) evolves towards ${\mathrm{FeSi}}_{2}$ with no change of symmetry, ie, the defect CsCl structure with a statistical occupation of metal sites remains epitaxially stable for all ${\mathrm{FeSi}}_{1+\mathit{x}}$ (0\ensuremath{\le}x\ensuremath{\le}1) Films thicker than -20 \AA{} exhibit a transition to the cubic \ensuremath{\epsilon}-FeSi phase The electronic band structure of FeSi (CsCl) has been calculated self-consistently using the full-potential linear augmented--plane-wave method

Magnetic anisotropies of ultrathin Co(001) films on Cu(001).

Abstract: We present experimental evidence that ferromagnetic order at room temperature in ultrathin epitaxial Co(001) layers on Cu(001) substrates is stabilized by in-plane magnetic anisotropies. All relevant anisotropy contributions have been determined as a function of Co layer thickness with and without an additional Cu overlayer.

Ferroelectric thin films prepared by sol-gel processing

Abstract: Ferroelectric thin films are playing a growing role as key elements in variety of devices. For various techniques of ferroelectric thin film preparation, the sol-gel processing is one of the most promising. In comparison with different deposition techniques, we survey the intrinsic advantages and the recent improvements of the sol-gel processing. In this review paper, several interesting topics, including epitaxial growth and grain-orientation, symmetric and asymmetric P-E hysteresis loops, heterojunction effect of the interface between film and substrate, to attest pyroelectricity of the films, electrooptic coefficients in poled and unpoled films, possibility of amorphous ferroelectrics, etc., are introduced.

Single‐crystal diamond plate liftoff achieved by ion implantation and subsequent annealing

Abstract: We describe a new method for removing thin, large area sheets of diamond from bulk or homoepitaxial diamond crystals. This method consists of an ion implantation step, followed by a selective etching procedure. High energy (4–5 MeV) implantation of carbon or oxygen ions creates a well‐defined layer of damaged diamond that is buried at a controlled depth below the surface. For C implantations, this layer is graphitized by annealing in vacuum, and then etched in either an acid solution, or by heating at 550–600 °C in oxygen. This process successfully lifts off the diamond plate above the graphite layer. For O implantations of a suitable dose (3×1017 cm−2 or greater), the liftoff is achieved by annealing in vacuum or flowing oxygen. In this case, the O required for etching of the graphitic layer is also supplied internally by the implantation. This liftoff method, combined with well‐established homoepitaxial growth processes, has considerable potential for the fabrication of large area single crystalline dia...

Epitaxial growth of BaTiO3 thin films by organometallic chemical vapor deposition

Abstract: Epitaxial BaTiO3 thin films were grown in situ on (100) LaAlO3 by low‐pressure organometallic chemical vapor deposition using the precursors Ba (hexafluoroacetylacetonate)2 (tetraglyme) and titanium tetraisopropoxide. The phase composition and epitaxial quality were sensitive to the reactant partial pressures and growth temperature. Deposition at 800 °C yielded [100]‐oriented BaTiO3 films. In‐plane epitaxy was confirmed for the BaTiO3 films by x‐ray diffraction.

Surface evolution during molecular-beam epitaxy deposition of GaAs.

Abstract: Scanning tunneling microscopy studies have been performed on GaAs homoepitaxial films grown by molecular-beam epitaxy. Images show that in the earliest stages of deposition the morphology oscillates between one with two-dimensional islands and flat terraces. As growth proceeds there is a gradual coarsening of the surface features. Comparison with reflection high-energy electron diffraction (RHEED) leads us to propose that there is a direct correspondence between the surface step density and the RHEED specular intensity. As such, we associate the decay of the RHEED oscillation amplitude with a reduction in the temporal variation of the step density rather than the buildup of interface width.

Growth kinetics of (100), (110), and (111) homoepitaxial diamond films

Abstract: We present the first investigation of the growth kinetics of diamond films grown homoepitaxially by hot‐filament chemical vapor deposition on (100), (110), and (111) natural diamond substrates. Growth rates on the various faces exhibited different functional dependencies on CH4 flow rate, being linear on (100), slightly sublinear on (110), and sigmoidal on (111). The temperature dependence of the growth rate was also crystal‐face‐dependent, yielding effective activation energies of 8±3, 18±2, and 12±4 kcal/mol for [100], [110], and [111] growth, respectively, at substrate temperatures between 735 and 970 °C. The apparent activation energies were considerably larger at substrate temperatures between 675 and 735 °C. We propose that these crystal face and temperature effects are due principally to differences and changes in the nanometer‐scale morphology and surface hydrogen coverage with methane concentration and surface temperature.

Synthesis of Si1−yCy alloys by molecular beam epitaxy

Abstract: We have synthesized pseudomorphic Si1−yCy (y≤0.05) alloys and strained layer superlattices on silicon by molecular beam epitaxy using solid sources for carbon and silicon. The introduction of C into substitutional sites in the silicon lattice is kinetically stabilized by low‐temperature growth conditions (500–600 °C) and relatively high Si fluxes, against extremely low C solubility (10−6 at 1420 °C) and the thermodynamically favored silicon carbide phases. Higher temperature growth leads to an islanded morphology. At lower temperatures, disruption of epitaxy occurs via the formation of highly twinned layers or even amorphous growth. The temperature window for alloy growth is reduced as the C concentration is increased. X‐ray diffraction, transmission electron microscopy, secondary ion mass spectroscopy, and Raman spectroscopy confirm the growth of pseudomorphic, tetragonally strained alloy layers with no detectable silicon carbide precipitation. These alloy layers allow for the engineering of Si‐based lat...

Light emitting diode

Abstract: PURPOSE:To form an edge light-emitting LED element whose light-emitting output change by a temperature is small by a method wherein an active layer is formed at an acute angle to an electrode and light is taken out directly in a direction which is nearly parallel to the electrode. CONSTITUTION:An n-type GaAs buffer layer 2 is grown heteroepitaxially on a low-resistance n-type Si substrate 1 by a molecular beam epitaxy method or an organometallic vapor growth method. In addition, an n-type GaAlAs layer 3, a GaAs active layer 4 and a p-type GaAlAs layer 5 are epitaxially grown sequentially; after that, one part is etched and removed. After that, an ITO 6 as a transparent conductive substrate is formed by a sputtering operation. The substrate 1 and the ITO 6 are polished and tilted with reference to the active layer 4. Au electrodes 7 high in reflectivity are formed on the substrate 1 and the ITO 6 by a sputtering operation. Thereby, it is possible to form an edge light-emitting LED element whose light-emitting change by a temperature is small.