Showing papers on "Epitaxy published in 1968"

Growth of Diamond Seed Crystals by Vapor Deposition

Abstract: Carbon was deposited on virgin, natural diamond powder from methane gas at 1050°C and 0.3 Torr. The deposits were identified as new diamond by chemical analysis, chemical etching, density measurements, x‐ray and electron diffraction, microwave absorption, electron spin resonance, and visual observations. The crystalline quality of the new diamond layers has not been established; it cound range from polycrystalline material with a large number of defects to true epitaxial layers.

Observation of ion bombardment damage in silicon

Abstract: Thin films of single crystals of both n-type and p-type silicon contain disordered zones ∼ 50 A in diameter, discernible in the electron microscope after bombardment with ∼ 1013 Ne+ ions cm−2. As the dose increases these zones become more numerous until eventually (≳ 1014 ions cm−2) they overlap, creating a continuous surface layer which electron diffraction shows to be amorphous silicon. The individual zones disappear on annealing between 400 and 500°C, and at ∼630°C the amorphous layer recrystallizes epitaxially upon the underlying silicon, leaving an array of dislocation loops and dipoles. The bombarded regions exhibit various hues until eventually when they become completely amorphous they appear ‘milky’ due to the Rayleigh scattering of light. This appearance has been used as a convenient method to study the ion dose needed to form amorphous silicon as a function of the temperature of the silicon during bombardment.

The Microstructure and Crystallography of Aluminium-Silicon Eutectic Alloys

Abstract: Aluminium-silicon alloys in the composition range 12 to 16 wt.% silicon have been frozen unidirectionally over a range of rates from ca . 0.3 to 30 μ m/s and with imposed temperature gradients ranging from 0.35 to ca . 40°C/mm. The detailed morphology and crystallography of silicon in these alloys are described and the various structures are rationalized in terms of the variables, composition, freezing rate and temperature gradient. Three growth processes are distinguished in which (A) massive silicon crystals grow at a planar aluminium front by a relatively long range diffusion process; (B) short range dif­fusion occurs at the growth front between silicon crystals which develop a preferred fibre texture; and (C) silicon crystals are more or less heavily twinned and grow by steady or fluctuating short-range diffusion processes. There do not appear to be any preferred epitaxial orientations between the phases. Similarities are noted between the microstructures of eutectic alloys in the systems Al-Si and Ag-Si, and it is shown that in chilled or ‘modified’ alloys the silicon occurs in an irregular fibrous form rather than as isolated globules. The mechanisms are discussed for (I) the growth kinetics of silicon, (II) the transition from a long-range to a short-range diffusion process, (III) steady-state, and (IV) non-steady-state growth processes, and (V) repeated nucleation of silicon crystals from the liquid.

Influence of Substrate Temperature on GaAs Epitaxial Deposition Rates

Abstract: The effects of substrate temperature on the GaAs deposition rates were studied for {111}A, {112}A, {113}A, {115}, {100}, {113}B, {112}B, and {111}B substrate orientations An open tube chloride transport system with elemental gallium and arsenic sources was employed This apparatus allowed independent control over the gallium monochloride, arsenic, and hydrogen chloride partial pressures The sensitivity of the deposition rate to substrate orientation is observed to be strongly temperature dependent Experimental evidence is provided which indicates that the deposition rate is kinetically limited in the temperature range from 725° to 800 °C

ROLE OF SURFACE DEFECTS IN THE EPITAXIAL GROWTH OF SOME fcc METALS ON POTASSIUM CHLORIDE CLEAVED IN ULTRAHIGH VACUUM.

Abstract: It has been found that surface defects produced by electron irradiation play a critical role in the formation of single‐crystalline films of typical fcc metals such as Au, Ag, and Cu on UHV‐cleaved KCl. Epitaxial films of the (100)Au∥(100)KCl, [100]Au∥[100]KCl orientation were produced in a wide range of substrate temperatures on irradiated surfaces at low supersaturation levels. Surface defects produced by irradiation provide nucleation sites which strongly favor the epitaxial orientation for nuclei. The high sensitivity of film orientation to irradiation treatment of the substrate suggests that other known critical factors such vacuum condition and surface composition may also influence epitaxy through their effect on the nature of the substrate surface upon which nucleation occurs.

The epitaxy of copper on sapphire

Abstract: Epitaxial twinned single‐crystal films of copper have been grown on sapphire substrates by high vacuum evaporation in the temperature range 240–‐375°C. The presence of a twin relationship in copper deposited on the basal plane of sapphire was demonstrated and evaluated by x‐ray diffraction techniques. The epitaxy has been shown to be (111)Cu ∥ (0001)α−Al2O3; [211)Cu ∥ [2110]α−Al2O3. The films have been found to exhibit the bulk metal resistivity.

The Defect Structure of GaP Crystals Grown from Gallium Solutions, Vapor Phase and Liquid Phase Epitaxial Deposition

Abstract: The defect structure of crystals grown from gallium solutions, vapor phase and liquid phase epitaxial deposition is described. Etchants have been used to demarcate emergent dislocations, stacking faults, and p‐n and n‐n+ junctions. Crystals grown from gallium solutions are inhomogeneous with respect to defect structure and contain substantial dislocation‐free regions. Evidence is cited which indicates that some dislocations are introduced during growth whereas others are apparently generated at high stress regions during cooling. It is demonstrated that vapor phase epitaxial deposition on substrates is capable of yielding nearly dislocation‐free crystals containing no stacking faults. The high density of defects observed in crystals grown on substrates is attributed to the heteroepitaxial mode of growth, in particular, the difference in thermal contraction of the growth layer and substrate on cooling from the growth temperature. diodes fabricated by liquid‐phase epitaxy, in contrast to those formed by vapor‐phase epitaxy, do not contain interfacial dislocations at the growth‐substrate interface, i.e., p‐n junction.

The epitaxial growth of zinc sulphide on silicon by vacuum evaporation

Abstract: Epitaxial layers, up to 5 μm thick, of zinc sulphide have been grown on thermally cleaned (111) surfaces of single-crystal silicon disks. The layers have been shown by x-ray and electron diffraction to be single-crystal and a continuation of the silicon lattice. The importance of producing a clean silicon surface and of maintaining constant temperatures during the deposition has been demonstrated.

Diffused diodes in silicon-on-sapphire

Abstract: The forward and reverse I–V characteristics of diffused diodes made in silicon grown epitaxially on sapphire have been measured. Silicon of doping density 4 × 10 15 to 6 × 10 17 /cm 3 p -type and 2 × 10 15 to 10 18 /cm 3 n -type have been used in these experiments. The forward conduction current of all diodes tested varied as exp ( qv /> nkT ) with n ≈ 1.7. Minority carrier lifetimes of the order 10 −10 sec have been inferred from the I–V data. The reverse currents were somewhat larger than predicted on the basis of currents generated in the space charge region but were reproducible from diode to diode. The temperature dependence of the diode currents was measured from room temperature to 200°C and followed the theoretical prediction. The variation of minority carrier lifetime with film thickness was measured, and the lifetime was found to increase as the silicon became thicker. Diodes produced by diffusion through the silicon to the silicon-sapphire interface were found to have minority carrier lifetimes about an order of magnitude lower than diodes not diffused to the bottom interface.

Method for epitaxially growing thin films

Abstract: A monocrystalline material of the formulation Hg(1 x)Cd(x)Te is grown epitaxially on a seed or substrate monocrystal of Cd Te, or the like. The reactants are mixed in the vapor phase and held at a temperature which prevents binary combinations. The ternary vapor phase mixture is then rapidly cooled to supersaturation and condensed on the seed crystal substrate. In a dynamic system, the mercury vapor acts as a carrier gas as well as a reactant.

Carrier Transport in Thin Silicon Films

Abstract: Films of p‐type and n‐type silicon 1–2 μ thick have been epitaxially grown on single‐crystal sapphire. The Hall mobilities of films with carrier concentrations varying between 1013/cc to mid‐1020/cc have been measured. For carrier concentrations above 1017/cc the mobility decreased with increasing carrier concentration similar to the drop in mobility observed in bulk silicon, indicating the dominance of impurity scattering at higher carrier concentrations. At lower carrier concentrations the scattering from crystalline defects limited the mobility to values approaching 30% of the mobility of bulk silicon. The presence of crystalline defects acting as electron traps was demonstrated by measuring the electron concentration in films of constant donor density but varying dislocation density and noting that the electron concentration dropped as the defect density rose. This has lead to an estimate of the electronically active defect density in thin silicon films grown epitaxially on sapphire of about 1015/cc‐1017/cc. Optical absorption data have indicated that there is considerable absorption at energies below 1.1 eV.

Compositional Inhomogeneities in GaAs1−xPx Alloy Epitaxial Layers

Abstract: Inhomogeneities in vapor‐grown epitaxial layers of Ga(As, P) alloys on GaAs substrates were studied by the electron microprobe, the divergent‐beam x‐ray method, and x‐ray topography. The epitaxial layers were prepared by growing a graded composition region between the substrate and the final GaAs1−xPx composition. The electron microprobe was used to determine the As/P ratio in the layer by scanning the cleaved edge of the epitaxial layer and substrate. The results showed two types of samples: those with composition steps in the graded composition region and those without these steps. Pseudo‐Kossel patterns for the composition steps as well as for the GaAs substrate and the GaAs1−xPx alloy surface layer are seen in the divergent x‐ray pattern photographs. The sharpness of the pseudo‐Kossel lines indicates that the degree of crystalline perfection decreased with increasing phosphorus content of the epitaxial layer. Lang topographs show that the accommodation for the lattice mismatch between the substrate an...

Technique for growth of epitaxial compound semiconductor films

Abstract: Epitaxial growth of Group III(a)-V(a) semiconductor compound films is effected in an ultrahigh vacuum by directing collimated molecular beams at the surface of a suitable substrate member preheated to a temperature ranging from 450*-650* C. The described process is a nonequilibrium growth technique which permits the growth of epitaxial films less than 1 micron in thickness at temperatures appreciably below those commonly employed in epitaxy.

Transmissive photocathode and devices utilizing the same

Abstract: Described are transmissive gallium arsenide photocathodes, and optical devices utilizing the same, comprising gallium arsenide epitaxially deposited on a layer of silicon, the gallium arsenide having absorbed into its surface electropositive metal atoms, preferably cesium. In one embodiment of the invention, the gallium arsenide is deposited on a silicon film epitaxially deposited on a transparent sapphire substrate; while in another embodiment, the gallium arsenide is deposited on a thin silicon web having a thickness in the range of about 10 to 25 microns.

Zener diode and method of making the same

Abstract: A Zener diode having a low dynamic impedance and a low leakage current which comprises a first layer of a single crystalline semiconductor of silicon doped with a P-type or N-type impurity and a second layer formed by gas-phase epitaxial growth of silicon and doped with an impurity of the opposite type. In the Zener diode, the impurity concentrations of the first and second layers are 1 X 1017 to 4 X 1019 atoms/cm.3 and 1 X 1019 to 1 X 1021 atoms/cm.3, respectively, and there is an impurity concentration gradient of from 2 X 1021 to 7 X 1023 atoms/cm.4 across the PN junction.

Electrical Properties of Single‐Crystal Gallium Phosphide Doped with Zinc

Abstract: Hall measurements have been made on epitaxially grown, zinc‐doped gallium phosphide, from which the gallium arsenide substrate had been removed The measurements were made in the temperature range from 300° to 4°K on samples whose room‐temperature carrier concentration varied from 7×1015 to 7×1018 cm−3 Using both van der Pauw and conventional Hall techniques on those samples which show a high degree of compensation, the variation of the ionization energy of zinc with concentration was determined Room‐temperature hole mobility varied from 60 to 100 cm2· V−1· sec−1 These observed hole mobilities are in good agreement with the calculated values of mobility due to reduced scattering by acoustical and optical phonons, and are shown to be too small to be accounted for by the mechanism of impurity scattering below 100°K Resistivity measurements made in the temperature range 77°–42°K show that in the impurity band conduction range, gallium phosphide behaves in a manner similar to impure germanium

Method of crystallizing a binary semiconductor compound

Abstract: A method of crystallizing a binary semiconductor compound from a liquid solution of the compound in one of its components, e.g. gallium arsenide in gallium. A small quantity of an element of the same group of the periodic system of the elements as that component, but having a larger atomic radius, e.g. indium, is added to the solution. The binary compound can be epitaxially deposited on the surface of a semiconductor body.

Method for epitaxially growing silicon carbide onto a crystalline substrate

Abstract: EPITAXIAL GROWTH OF SEMICONDUCTIVE MATERIALS IS EFFECTED IN AN INERT ATMOSPHERE BY PHYSICALLY CONTACTING THE SURFACES OF A SOURCE OF SEMICONDUCTIVE MATERIAL TO PARTICULAR SUFACE AREAS OF A CRYSTALLINE SUBSTRATE ONTO WHICH SUCH SURFACE AREAS OF A CRYSTALLINE SUBSTRATE ONTO WHICH SUCH GROWTH IS TO BE EFFECTED. THE SOURCE IS HEATED TO A TEMPERATURE TO CAUSE RAPID VAPORIZATION OF THE SEMI-CONDUCTIVE MATERIAL; THE SUBSTRATE IS MAINTAINED AT A SLIGHTLY LOWER TEMPERATURE TO PROMOTE THE CONDENSATION AND EPITAXIAL GROWTH OF THE VAPORIZED SEMICONDUCTIVE MATERIAL ON THE CONTACTED SUBSTRATE SURFACES. THE SURFACE OF THE SOURCE CAN BE PREFORMED SO AS TO GROW PARTICULAR PATTERNS OF THE SEMICONDUCTIVE MATERIAL ONTO THE SUBSTRATE SURFACE. CONDUCTIVITY-TYPE DETERMINING IMPURITIES CAN BE INTRODUCED EITHER INTO THE INERT ATMOSPHERE OR BE PRESENT IN THE SOURCE SO AS TO IMPART A PARTICULAR CONDUCTIVITY TO THE GROWN SEMICONDUCTIVE MATERIAL.

Plastic Deformation in Epitaxial Ge Layers Grown on Single Crystal Semi‐Insulating GaAs

Abstract: The compatibility of Ge and , in terms of their temperature dependent mechanical properties, is described in this paper. Examination at room temperature of epitaxial Ge layers grown on wafers of single crystal, semi‐insulating , at substrate temperatures of 700°C by pyrolytic dissociation of , reveals evidence of plastic deformation immediately following the epitaxial deposition process. Plastic deformation is observed in epitaxial Ge layers grown at 350°C, by disproportionation of , only after a subsequent annealing cycle to at least 500°C. The low substrate temperature Ge films, however, show elastic bending of thin substrates after deposition and cooling to room temperature. Based on these observations, it is possible to estimate the differential thermal expansion coefficient between Ge and , and to use this result to estimate the critical shear stress for plastic deformation under low strain rate conditions . Interface dislocations are not observed.

Electrical Properties of n‐Type Epitaxial Films of Silicon on Sapphire Formed by Vacuum Evaporation

Abstract: n‐type epitaxial films of silicon on sapphire were successfully obtained with a high degree of reproducibility by adding antimony during the evaporation of undoped silicon having the resistivity of 2400 Ω·cm. An attempt to control resistivities of films was made by changing the temperatures of the antimony source. The dependence of the Hall mobilities and the carrier concentrations of the films upon temperatures was measured at temperatures ranging from 77°K to room temperature. The Hall mobility of films grown on (0001) sapphire at a substrate temperature of 900°C was higher than that of films with a similar resistivity grown on(1012) sapphire. Effects of the thermal oxidation and the subsequent annealing of these as‐grown films upon their electrical properties were investigated. After these treatments a remarkable rise in the Hall mobilities of the films was observed at temperatures ranging from 77°K to room temperature.