Showing papers on "Epitaxy published in 1985"

Limited reaction processing: Silicon epitaxy

Abstract: We introduce a new technique, limited reaction processing, in which radiant heating is used to provide rapid, precise changes in the temperature of a substrate to control surface reactions. This process was used to fabricate thin layers of high quality epitaxial silicon. Abrupt transitions in doping concentration at the epitaxial layer/substrate interface were achieved for undoped films deposited on heavily doped substrates.

Crystal orientation dependence of silicon doping in molecular beam epitaxial AlGaAs/GaAs heterostructures

Abstract: Results on crystal orientation dependence of n‐ and p‐type Si doping in molecular beam epitaxial GaAs are presented. High electron and hole mobilities in AlGaAs/GaAs heterostructures on high index planes are demonstrated for the first time. The doping results should prove useful for various transistor structures and complementary circuits. Also, due to the differences in the band structure for different orientations, quantum well heterostructures are likely to exhibit many interesting phenomena which are strongly orientation dependent.

Growth and properties of GaAs/AlGaAs on nonpolar substrates using molecular beam epitaxy

Abstract: Using molecular beam epitaxy, we have successfully grown device quality GaAs/AlGaAs on (100)‐oriented Ge and Si substrates. Modulation doped field effect transistors have been fabricated from these layers which exhibit room‐temperature transconductances as high as 160 and 170 mS/mm for layers on Ge and Si, respectively, and showed no looping in either case. At 77 K, these values rose to 345 and 275 mS/mm for Ge and Si, respectively. Analysis by transmission electron microscopy of layers grown on Ge showed that the antiphase disorder was contained within the 250‐A‐thick initial layer which was grown at a 0.1‐μ/h growth rate at a substrate temperature of 500 °C. For both the layers grown on Si and Ge specular surface morphologies were obtained. The photoluminescence of GaAs/AlGaAs quantum wells grown on Si and Ge was similar in intensity to the same quantum well structures grown on GaAs. In quantum wells grown on Ge, the luminescence was dominated by a donor‐acceptor recombination at 1.479 eV, which appears to be Ge0Ga ‐Ge0As. These results show that high‐quality GaAs/AlGaAs is obtainable on nonpolar substrates, which has important implications for the monolithic integration of III‐V’s with Si.

High efficiency indium tin oxide/indium phosphide solar cells

Abstract: Improvements in the performance of indium tin oxide (ITO)/indium phosphide solar cells have been realized by the dc magnetron sputter deposition of n-ITO onto an epitaxial p/p(+) structure grown on commercial p(+) bulk substrates. The highest efficiency cells were achieved when the surface of the epilayer was exposed to an Ar/H2 plasma before depositing the bulk of the ITO in a more typical Ar/O2 plasma. With H2 processing, global efficiencies of 18.9 percent were achieved. It is suggested that the excellent performance of these solar cells results from the optimization of the doping, thickness, transport, and surface properties of the p-type base, as well as from better control over the ITO deposition procedure.

Atomic layer epitaxy of III‐V binary compounds

Abstract: Atomic layer epitaxy (ALE) of III‐V semiconductors is reported for the first time using metalorganic and hydride sources. This is achieved by using a new growth chamber and susceptor design which incorporates a shuttering mechanism to allow successive exposure to streams of gases from the two sources. Also, most of the gaseous boundary layer is sheared off after exposure to the gas streams. GaAs and AlAs deposited by ALE are single crystal and show good optical properties.

Silicon epitaxy at 650–800 °C using low‐pressure chemical vapor deposition both with and without plasma enhancement

Abstract: A system and a procedure using chemical vapor deposition of silane at very low pressures (<10−2 Torr) have been developed for depositing uniform, specular silicon epitaxial films both with and without plasma enhancement at temperatures as low as 650 °C. In situ cleaning of the substrate surface that overlaps into the deposition is the most critical aspect of the procedure. Undoped films deposited on substrates heavily doped with antimony or boron have abrupt doping profiles. Preliminary measurements indicate that the hole mobility of epitaxial films obtained with this process is 90% of that in bulk silicon. Films oxidized and decorated with a Secco etch show twice as many defects as a similarly treated substrate. Nonplasma growth kinetics are sensitive to surface conditions such as crystallographic orientation, and surface diffusion of adsorbed species appears to be the rate‐limiting step for depositing epitaxial films above 700 °C. Around 650 °C, the growth mechanism appears to change, possibly due to th...

Epitaxial growth and characterization of CaF2 on Si

Abstract: CaF2 films have been grown epitaxially on (100) and (111) Si substrates by molecular beam epitaxy. These films have been characterized by electron microscopy, reflection high‐energy electron diffraction, Rutherford backscattering ion channeling, and back‐reflection Laue x‐ray diffraction. In addition, chemical etching has been used to reveal dislocations and to delineate cracks. Film cracking appears to be related to crystalline perfection through misfit dislocation mobility. It is possible to grow high quality, (xmin=3.0%) single‐crystal films on (111) Si which are free of cracks and atomically flat. However, the high free energy of the (100) surface in an ionic fluorite crystal prevents the growth of comparable CaF2 films on the (100) Si surface.

Growth of thin-film lithium niobate by molecular beam epitaxy

Abstract: Lithium niobate has been grown in single-crystal thin-film form by molecular beam epitaxy. Single-crystal films were grown on bulk-crystal LiNbO3 and on sapphire (α-Al2O3). The layers have been excited as optical waveguides, and the refractive indices and optical propagation loss were measured.

Spin separation in a metal overlayer.

Abstract: The electronic properties of a ferromagnetic Fe monolayer epitaxially adsorbed on a Ag{100} substrate have been computed fully self-consistently. The minority $d$-band spin states of the Fe overlayer were found to be separated energetically from the majority-spin band. The magnetic moment per overlayer atom is 3.0${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$, 36% larger than that of bulk iron.

High resolution electron microscope study of epitaxial CdTe‐GaAs interfaces

Abstract: CdTe films have been grown on (100) GaAs substrates with two different epitaxial relations: (111)CdTe∥(100)GaAs and (100)CdTe∥(100)GaAs. High resolution electron microscope observation of these two types of interfaces was carried out in order to investigate the role of the substrate surface microstructure in determining which type of epitaxy occurs. The interface of the former type shows a direct contact between the CdTe and GaAs crystals, while the interface of the latter type has a very thin layer (∼10 A in thickness), which is most likely an oxide, between the two crystals. These observations suggest that the GaAs substrate preheating cycle prior to CdTe film growth is crucial in determining which type of epitaxy occurs in this system.

Strained-Layer Epitaxy of Germanium-Silicon Alloys

Abstract: Despite the dominant position of silicon in semiconductor electronics, its use is ultimately limited by its incompatibility with other semiconducting materials. Strained-layer epitaxy overcomes problems of crystallographic compatibility and produces high-quality heterostructures of germanium-silicon layers on silicon. This opens the door to a range of electronic and photonic devices that are based on bandstructure physics.

Non‐alloyed ohmic contact to n‐GaAs by solid phase epitaxy

Abstract: A non‐alloyed ohmic contact to n‐type GaAs has been demonstrated. The technique of solid phase epitaxy through a transport medium has been used to obtain a metal/Ge(n+, epi)/GaAs(n, 〈100〉) heterostructure. The resulting contact displays a smooth surface and low contact resistivity (∼10−6–10−5 Ω cm2) when compared with standard Au‐Ge contacts on n‐GaAs with similar doping concentrations (∼1018/cm3).

Photoluminescence of CdTe: A comparison of bulk and epitaxial material

Abstract: Photoluminescence (PL) studies of bulk and epitaxial CdTe samples obtained from several sources are discussed. Steady state PL measurements were carried out at temperatures ranging from 16–300 K. The effects of surface preparation, substrate temperature, and film thickness were studied in detail for homoepitaxial films grown on the (111)A and (100) planes of CdTe. PL studies of epitaxial CdTe films grown on (0001) sapphire by molecular beam epitaxy (MBE), by hot wall MBE, and by metal‐organic chemical vapor deposition (MOCVD), and on the (111)B and (100) planes of GaAs by MBE have also been completed. The CdTe epilayers on sapphire and GaAs substrates typically display a bright PL spectrum dominated by the near edge peak at 1.58 eV (77 K). In addition, a number of films exhibit a near edge peak at 1.503 eV at 300 K, which is indicative of high quality epitaxy and which allowed direct measurement of the room temperature band gap of CdTe. PL studies of epitaxial Cd1−x MnxTe films grown by MBE on 5.0 μm thic...

Selective epitaxial growth method

Abstract: PURPOSE:To eliminate generation of crystal defect at the periphery of semiconductor layer and obtain flat grown layer by providing an aperture through anisotropic dry etching and realizing epitaxial growth under a reduced pressure of at least 100Torr or less with the remaining film used as the mask, at the time of boring an aperture to an insulating film deposited on the surface of semiconductor substrate and forming a semiconductor layer by the epitaxial growth on the exposed substrate surface. CONSTITUTION:An SiO2 insulating film 2 is deposited on the surface of a semiconductor substrate 1, the area other than the specified region is covered with a resist film 3 by the photo-engraving method, and an aperture 6 is formed on the film 2 by the parallel flat plate type anisotropic dry etching apparatus with the mixed gas of CF4 and H2 used as the etchant. Then, the film 3 unwanted is removed and a semiconductor layer 7 is formed by the epitaxial growth method on the substrate 1 exposed to the aperture 6 under the reduced pressure condition. In this case, a mixed gas of H2 carrier gas and SiH2Cl2 is used, pressure is set to 100Torr or less and temperature is set to 900-1,100 deg.C for the epitaxial growth.

Characterization of epitaxially grown GaAs on Si substrates with III‐V compounds intermediate layers by metalorganic chemical vapor deposition

Abstract: GaAs grown on Si substrate with AlP, AlGaP, GaP/GaAs0.5P0.5 superlattice, and GaAs0.5P0.5/GaAs superlattice was investigated by varying the structure of the intermediate layers between GaAs and Si by metalorganic chemical vapor deposition. It was found that (1) the insertion of AlP and AlGaP layers makes the crystallinity and the surface morphology better, (2) PL (photoluminescence) intensity with two superlattice layers is about one order of magnitude stronger than that without these layers, (3) the crack formation in the GaAs surface layer can be avoided by the strained superlattice layers, (4) the PL intensity has a maximum at about 20 nm for each layer thickness in the superlattices, and (5) the PL intensity increases and the carrier concentration decreases while increasing the thickness of the surface GaAs and saturates over 3 μm. The PL intensity of GaAs on Si substrates is about 80% of that grown on GaAs substrates.

Flow-Rate Modulation Epitaxy of GaAs

Abstract: We propose a flow-rate modulation epitaxy method which yields high-purity GaAs layers with improved growth rate controllability. This method is based on an alternate gas flow of triethyl gallium (TEG) and arsine (AsH3) by using hydrogen carrier gas. The most characteristic point of this method is that a very small amount of AsH3 is added during the TEG flow period. This small amount of AsH3 suppresses the formation of arsenic vacancies near the growing surface, and thus reduces the incorporation of impurity atoms. As a result, we could obtain high purity GaAs layer at relatively low growth temperatures.

Metalorganic Molecular-Beam Epitaxial Growth and Characterization of GaAs Using Trimethyl- and Triethyl-Gallium Sources

Abstract: The metalorganic molecular-bean epitaxial (MOMBE) growth of GaAs using trimethylgallium and triethylgallium has been studied. The results of introducing hydrogen into the system are also descrived. Introducing ionized hydrogen into the TMG-As4 system reduced the carrier concentration from 1×1020 cm-3 to 1×1018 cm-3. Using TEG as a Ga source, epitaxial layers grown at temperatures below 580°C showed n-type conduction and a carrier concentration of about 1×1017 cm-3, while those grown at higher temperatures showed p-type conduction.

Surface layer spinodal decomposition in In1−xGaxAsyP1−y and In1−xGaxAs grown by hydride transport vapor‐phase epitaxy

Abstract: Composition modulation due to spinodal decomposition in In1−xGaxAsyP1−y quaternary and In1−xGaxAs ternary alloys is observed by transmission electron microscopy in epitaxial layers grown by hydride transport vapor phase epitaxy at 700 °C on (001) InP substrate A quasi‐periodic fine contrast oriented along [100] and [010] directions is found in all samples over a composition range of 020≤x≤053 and 037≤y≤1 Contrary to the result reported on materials grown by liquid‐phase epitaxy, complete mixing at composition outside the miscibility gap predicted by thermodynamics for bulk crystals is not observed The evidence indicates a rapid spinodal decomposition by surface diffusion during vapor phase deposition Furthermore, transmission electron microscopy diffraction contrast experiments on the (110) cross‐sectional view of planar and nonplanar epitaxial layers reveal a columnar structure oriented along the growth direction which is consistent with the surface layer spinodal formation Additional coarse cont

Method of producing a thin silicon-on-insulator layer

Abstract: A method of forming a thin silicon layer upon which semiconductor devices may be constructed. An epitaxial layer is grown on a silicon substrate, and oxygen or nitrogen ions are implanted into the epitaxial layer in order to form a buried etch-stop layer therein. An oxide layer is grown on the epitaxial layer, and is used to form a bond to a mechanical support wafer. The silicon substrate is removed using grinding and/or HNA, the upper portions of the epitaxy are removed using EDP, EPP or KOH, and the etch-stop is removed using a non-selective etch. The remaining portions of the epitaxy forms the thin silicon layer. Due to the uniformity of the implanted ions, the thin silicon layer has a very uniform thickness.

Growth and characterization of GaAs/Ge epilayers grown on Si substrates by molecular beam epitaxy

Abstract: Epitaxial GaAs/Ge films are grown by molecular beam epitaxy (MBE) on Si substrates. The effect of various MBE growth conditions on the sample morphology, the defect density, and the optical properties of GaAs and Ge epilayers is examined. Scanning electron microscopy, plan‐view and cross‐sectional transmission electron microscopy, reflection high‐energy electron diffraction, and photoluminescence are used to characterize epitaxial layers. It is found that the defect density decreases with increasing epilayer thickness. This is due to an annihilation process that affects both threading dislocations and stacking faults. The substrate temperature during Ge growth is found to affect the properties of both the Ge and GaAs films. GaAs surface morphology degrades and the stacking fault density increases at high Ge buffer‐layer substrate temperatures; however, the threading dislocation density remains unchanged. Variations in growth conditions are correlated with defect densities and luminescence efficiencies to determine material quality and optimize growth conditions.

Lateral p-n junction formation in GaAs molecular beam epitaxy by crystal plane dependent doping

Abstract: Lateral p‐n junctions have been formed during the growth of GaAs by molecular beam epitaxy. Using a GaAs substrate which consisted of side‐by‐side {100} and {111} A planes formed by plane‐selective etching, Si‐doped GaAs was found to grow with p‐type conductivity on the {111} A planes, while n‐type material was grown simultaneously on the {100} planes. n‐p‐n structures with p‐type regions as narrow as 2 μm were grown. Conductivity measurements on narrow stripes of p‐type material formed by GaAs growth on {111} A planes indicate that Si was efficiently incorporated as an acceptor under the growth conditions used for this experiment.

Growth of InAs1−xSbx (0<x<1) and InSb‐InAsSb superlattices by molecular beam epitaxy

Abstract: Thin films of InAs1−xSbx (0

Reduction of background doping in metalorganic vapor phase epitaxy of GaAs using triethylgallium at low reactor pressures

Abstract: The mechanism of background impurity incorporation in the metalorganic vapor phase epitaxy of GaAs using triethylgallium and arsine was investigated over a wide range of growth parameters The growth temperature, total reactor pressure, AsH3/Ga(C2H5)3 ratio, and the linear gas velocity were altered in order to ascertain the primary determinants of the background impurity incorporation in the ethyl based chemistry The GaAs electrical and optical properties are, in general, independent of AsH3/Ga(C2H5)3 ratio but strongly dependent on growth temperature and reactor pressure Reductions in the reactor pressure, at a constant mass flow rate, result in a linear decrease in the unintentional impurity incorporation, while not changing the growth rate Substantial improvements in the layer purity with greatly reduced AsH3 consumption can be achieved A general model of impurity incorporation which relates the effect of reactor pressure and impurity incorporation is presented

Room-temperature GaInAsSb/AlGaAsSb DH injection lasers at 2.2 μm

Abstract: Double-heterostructure lasers based on the GaInAsSb/AlGaAsSb system have been prepared by liquid-phase epitaxy and operated in the 22 μm-wavelength region Room-temperature, pulsed threshold current densities of 6 kA/cm2 and characteristic temperatures of T 0= 85 K have been obtained

Growth of crystalline zirconium dioxide films on silicon

Abstract: Zirconium dioxide (ZrO2) films have been grown on Si(100), Si(111), and SiO2/Si substrates heated at the range from room temperature to 800 °C by vacuum evaporation. X‐ray diffraction and reflection high‐energy electron diffraction observations reveal the epitaxial growth of tetragonal ZrO2(200) films on Si(100) substrates at 800 °C. The epitaxial imperfection is caused by preferentially oriented tetragonal ZrO2(002) grains. The crystalline system of ZrO2 films depends on the substrate temperature. The crystalline perfection and the orientation of tetragonal ZrO2 films grown at 800 °C depend on the substrate orientation.

Structure and morphology of polycrystalline silicon‐single crystal silicon interfaces

Abstract: Using high resolution transmission electron microscopy, morphological aspects of the polycrystalline silicon (polysilicon)‐single crystal silicon interface have been correlated to the surface treatment used prior to polysilicon deposition, and to high‐temperature annealing. Specimens which were chemically oxidized prior to the deposition exhibited a continuous layer of amorphous oxide ∼15 A thick; high‐temperature annealing results in the formation of small discontinuities in this oxide, and thus small regions of epitaxial realignment within the polysilicon layer. Specimens which were etched in HF prior to deposition were characterized by nearly oxide‐free interfaces, and, following high‐temperature annealing, exhibited regions of epitaxial realignment an order of magnitude larger than those found in the chemically oxidized samples.

Electrical properties of CdTe films and junctions

Abstract: Polycrystalline films of CdTe have been deposited on graphite substrates, and homoepitaxial films on single‐crystal CdTe:P substrates, with hole densities as high as 1.5×1016 cm−3 without intentional doping of the films, using close‐spaced vapor transport. The dependence of hole density in the films on the properties of the source, the properties of the substrate, the growth rate, and the substrate temperature, indicates that the doping of the films is the result of a complex interaction between out‐diffusion of mobile impurities (if present) from the substrate and intrinsic defects. The capacitance‐versus‐voltage‐indicated hole density decreases slowly with time under a Schottky barrier, but not at a free film surface or under a CdS/CdTe heterojunction. CdS/CdTe solar cells have been prepared using these films, with solar efficiencies greater than 6%. The junction properties of CdS/CdTe heterojunctions are compared with those of In/CdTe Schottky barriers as a function of temperature; transport is dominat...

Investigation of surface roughness of molecular beam epitaxy Ga1−xAlxAs layers and its consequences on GaAs/Ga1−xAlxAs heterostructures

Abstract: We report a detailed investigation of the surface morphology of Ga1−xAlxAs layers grown by molecular beam epitaxy (MBE) as a function of the layer parameters and the growth conditions. Under some conditions Ga1−xAlxAs layers exhibit a surface roughness characterized by a degradation of the in situ electron diffraction pattern and a very broad photoluminescence peak. The amplitude of the roughness, as observed by optical microscopy and measured by alphastep profiler, increases with the layer thickness, the growth rate r, and goes through a maximum for a substrate temperature TS≂650 °C, a flux ratio R=JV/JIII≂6 and an Al composition x≂0.5. However, smooth layers can be obtained using growth conditions like high TS (≥700 °C), low flux ratio (R≤2.5), or low growth rate (<0.5 μm/h). No surface roughness was observed for GaAs and AlAs layers. Moreover, a high concentration of foreign atoms at the surface of the growing layer (Sn dopant for example) yields to a quite perfect surface morphology. This paper also c...