Epitaxial Single Crystals Research Articles

Growth and Characterization of Single Crystal Epitaxial CoGa on MBE Grown III-V Semiconductors

ABSTRACTWe have demonstrated growth of high quality single crystal CoGa films on Ga1−xAlxAs. These films were fabricated in-situ by codeposition of Co and Ga on MBE grown Ga1−xAlxAs(100) surfaces. The elemental composition of the films was determined using Rutherford Backscattering (RBS) and in-situ Auger analysis. The structural quality of the films' surfaces was studied using RHEED (during deposition) and LEED (post deposition). RBS channeling was used to determine the bulk crystalline quality of these films.For ∼500 Å CoGa films grown at ∼450°C substrate temperature, channeling data showed good quality epitaxial single crystals [χmin ∼7%] with minimal dechanneling at the interface.

Measurement of charge-carrier concentration in indium phosphide by means of an electrolyte-semiconductor contact

An electrolyte-semiconductor contact is used to study the conductivity of epitaxial layers and single crystals of n-type indium phosphide obtained by gas transport. Some of the specimens were alloyed with tin and sulfur. The voltfarad characteristics are used to find the potentials of planar zones, which amount to 0.8–1.3 V for different electrolytes. Values of concentration of charge carriers calculated from measured values of capacitance of the electrolyte-indium-phosphide contact showed good agreement with measurements of the Hall effect on single crystals in the range 1016-1018cm−3. The use of measurements of the capacitance of the electrolyte-semiconductor contact with simultaneous etching of a local region made it possible to study the electron distribution in epitaxial layers of indium phosphide.

Optical, Vibrational and Surface Properties of SiC

ABSTRACTA short historical introduction concentrates on key experimental and theoretical developments prior to the mid-seventies which form the basis of our present understanding of the semiconducting and optical properties of the polytypes of SiC. Selected research of the last decade is reviewed. Finally, we discuss our on-going surface and defect studies in both epitaxial single crystal films of 3C SiC and other hexagonal SiC polytypes.

Properties and ion implantation of AlxGa1−xN epitaxial single crystal films prepared by low pressure metalorganic chemical vapor deposition

High quality single crystal films of AlxGa1−xN have been grown on sapphire substrates using low pressure metalorganic chemical vapor deposition at 915 °C over the entire range of x. Electrical and optical properties of the layers were measured. Electrical compensation by Be+ and N+ implants in the layers was studied. Schottky barriers were fabricated and their current voltage characteristics were studied. We also report some initial results of a study of GaN growth kinetics.

Ferromagnetic resonance studies of very thin epitaxial single crystals of iron

Ferromagnetic resonance (FMR) has been used to study a wide variety of very thin single crystals of Fe grown on (110) GaAs substrates by molecular beam epitaxy. Data were taken at room and liquid nitrogen temperatures for films with thicknesses L in the range 18–200 Å. Due to surface anisotropy, the easy axis of the magnetization switches from [100] to [110] when L≤50 Å, independent of whether the the film surface is passivated by an Al-overcoat or has a thin Fe oxide surface layer. We suggest that this is an effective surface anisotropy arising in part from a depth dependent strain near the film-substrate interface. The changes in the parameters describing the angular dependence of the FMR spectra upon cooling to 77 K can be explained as due to magnetostriction arising from thermally induced strains plus the temperature dependence of the cubic volume anisotropy. The FMR linewidth is shown to be a linear function of frequency in the range 5–40 GHz.

Hetero-epitaxial growth of Mo single crystal films on MgO-crystals and of W, Nb, and Ta on Mo thin film substrates

Epitaxial thin single crystal films of molybdenum have been deposited on MgO bulk crystals by high vacuum evaporation. The favourable substrate temperature was between 1100°C and 1150°C at a deposition rate of 20 Å/s. The Mo films served as substrates for the epitaxial growth of W, Nb and Ta crystals. The deposited films were examined by X-ray studies and TEM.

Transport Coefficients and Structural Principles of PbOGa2O3 Melt

AbstractMore Precise knowledge of the growth mechanism of garnets in form of epitaxial layers or single crystals in high temperature solutions on the base of trivalent oxides Me2O3 in PbOB2O3 solvent is desirable. Data of physicochemical properties of the melts especially density, shear viscosity, and electrical conductivity and their dependence on the temperature are useful in endeavour to recognize the structural principles of oxidie melts. Therefore as a first step the binary system PbOGa2O3 was investigated to understand the influence of the Ga component on a complete mixed garnet solution, for instance (Y, Sm)3 (Fe, Ga)5O12 in PbOB2O3 solvent.

The optical absorption edge of single-crystal AlN prepared by a close-spaced vapor process

We have prepared several thicknesses of ∼1 cm by ∼1 cm epitaxial single crystals of AlN with a ’’high temperature (∼1800 °C) close-spaced vapor transport’’ technique. These crystals have been grown both on (011̄2) and (0001) sapphire wafers. The optical absorption edge is measured at 300 K and for the first time at low temperature (5 K). This data is parametrized to include both reflection losses due to scattering off surface imperfections and contributions from impurity absorption bands. This parametrization technique is used to determine the band gap and the nature, direct or indirect, of the absorption edge. A value of 6.28 eV was found to be the best value of Eg(5 K) and the gap was found to be direct.

The oxidation of Zn(0001): The first stage

The oxidation of the basal plane of zinc has been observed to have several distinct stages in a study using Auger electron spectroscopy and low-energy electron diffraction. For oxygen pressures between 10 −8 and 10 −6 Torr and substrate temperatures between liquid N 2 temperature and 425°K, the first stage of the oxide growth is described by a substrate temperature independent, linear rate law: dx dt = k 0P , where x is the film thickness, P is the oxygen pressure and k 0 is a constant with a magnitude of about 10 −3 cm/Torr·sec. The first stage of growth stops after an exposure of about 8×10 −5 Torr·sec after an oxide film several monolayers thick has formed. For T 300°K, the oxide film is an epitaxial single crystal with lattice constant parallel to the Zn substrate and equal to that of bulk zinc oxide. For T 250°K, no long range order was observed. Mechanisms which are consistent with the observed growth kinetics are discussed.

Preparation and properties of MgO single crystals grown by chemical vapor deposition

Growth of MgO single crystals by dynamic chemical vapor deposition has been achieved by generating MgCl 2 vapor by the reaction: MgO ( s) + Cl 2 ( g) + CO ( g) ⇄ MgCl 2 ( g) + CO 2 ( g) and subsequently inducing MgO deposition by adding hydrogen to give: MgCl 2 ( g) + CO 2 ( g) + H 2 ( g) ⇄ MgO ( s) + 2 HCl ( g) + CO ( g) all at 1600 °C and a total pressure of 5 torr. The influence of gas flow rate, temperature and oxidizing potential on epitaxial single crystal growth, needle growth and powder formation due to nucleation in the gas phase is reported. Epitaxial single crystals 1 × 1 × 0.2 cm were grown at rates of 4.2 × 10 ×6 cm/ sec; 1.5 × 0.3 × 0.2 cm needles were grown at linear rates of 2.8 × 10 ×5 cm⧸ sec. Chemical analysis indicated less than 150 ppm by weight, cation impurity, and dislocation densities were 5 × 10 3/ cm 2.

Epitaxial growth of very pure NiO single crystals

This paper describes the procedure for growing epitaxial single crystals of NiO with a minimum content of impurities. Particular attention is paid to details of the starting material as well as to the cleaning and handling of the apparatus. Crystals with a total cation impurity content of less than 20 ppm are now grown routinely.

Gamma-Radiation Damage in Epitaxial Gallium Arsenide

Electrical and photoluminescence measurements were carried out on liquid epitaxial GaAs single crystals after irradiation at room temperature by 1.25-MeV 60Co γ rays. Following each of a series of irradiations, Hall measurements were made on both n- and p-type crystals as a function of temperature between 77 and 300°K. The n-type crystals exhibited energy levels 0.13, 0.16, and 0.30 eV below the conduction band minimum after irradiation. The 0.13- and 0.16-eV levels were introduced during irradiation at roughly one-half the rate at which compensating deep acceptors were introduced. The p-type crystals showed energy levels 0.059 and 0.10 eV above the valence band maximum. Before irradiation, these p-type crystals had energy levels in the lower 0.20 eV level of the band gap. It is, therefore, not possible to determine whether the 0.059 and 0.10 eV were produced by irradiation or were merely uncovered as the free-hole density was reduced by radiation-induced deep donors. The carrier removal rate at 77°K was 0.012 cm−1 for p-type crystals. Photoluminescence measurements on irradiated material revealed additional energy levels near the center of the band gap.

The epitaxy of zinc sulphide on silicon

The epitaxy of zinc sulphide films on silicon has been studied by means of X-ray and electron diffraction and by scanning electron microscopy. Results have shown that due to the nature of the stacking of atoms, planar defects will predominate in such a sphalerite structure material; this is similar to the results of Pashley and Stowell on face centred cubic metals. Such defects have been shown to be more prevalent on (111) and (110) orientations, compared with the (100) orientation which gave the best epitaxial single crystal films. These results agree with other work from this laboratory on the epitaxy of zinc selenide on germanium and silicon.

Epitaxial Growth of Titanium Films on Mica

The oriented overgrowth of titanium films obtained by evaporation in an ultrahigh-vacuum system onto mica was studied in situ by reflection electron diffraction and, after withdrawal from the system, by transmission electron microscopy and diffraction. Films with a thickness of 100 Å or more, prepared on a mica at temperatures of 500°–600°C, are epitaxial single crystals of hexagonal structure; their basal plane is parallel to that of the substrate and the crystallographic axes within the contact planes form an average angle of 30°. These single-crystal films have a smooth surface and are composed of subgrains rotated around the c axis with respect to each other, forming angles up to 4°. Films thinner than 100 Å are only partially oriented. Coalescence in these films takes place at a very early stage of growth and continuous films of about 100 Å are obtained, in contrast with the growth of other metals on mica.

Homogeneous solution grown epitaxial GaAs by tin doping

Tin doped epitaxial GaAs single crystals were grown from a Ga solution. The C-V characteristics of Schottky barrier diodes were used to determine the electron concentration profiles of the GaAs crystals. These profiles were flat within ± 5 per cent to a depth of 165 μ. The electron concentration was controlled at specified values between 3 × 10 14 and 5 × 10 16 cm −3. The distribution coefficient of tin in GaAs is 1 × 10 −4 between 800 and 850°C.