Infrared angular spectroscopy characterization of epitaxial layers of n-type silicon grown on N+ or P+ substrates

Summary In this paper the technique of infrared angular spectroscopy applied to the characterization of epitaxial layers ofn-type silicon grown on N⁺ or P⁺ substrates is illustrated. Some results are reported and discussed concerning films having a free-carrier concentration ranging from 10¹⁴ cm⁻³ to 10¹⁷ cm⁻³ and thickness of the order of 10 μm. A significant comparison with results obtained by other techniques (four-point probe, spreading resistance,C−V plots, etc.) is performed and a few simple conclusions are drawn. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Recombination at mixed-valence impurity centers in PbTe(Ga) epitaxial layers

The photoconductivity kinetics in PbTe(Ga) epitaxial films prepared by the hot-wall method is studied. The recombination of nonequilibrium photoexcited electrons at low temperatures was found to proceed in two stages, with a period of relatively fast relaxation followed by delayed photoconductivity. The temperature at which delayed photoconductivity appears increases with decreasing film thickness. The relaxation rate over the period of fast relaxation depends on film thickness and is the lowest in the thinnest layers. In semi-insulating films, photoconductivity is always positive, whereas in samples with lower electrical resistivity positive and negative photoconductivities are observed to coexist. The data obtained are discussed in terms of a model in which the impurity gallium atom can be in more than one charged state.     

Graphical method for determining the electrical parameters of epitaxial layers of n-type gallium arsenide and phosphide

The electrical parameters of epitaxial layers of n-type GaAs and GaP were determined by graphical analysis of the temperature dependence of the Hall coefficient with the help of the neutrality condition. The method is developed for application to both shallow and deep impurity levels.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 21–26, October, 1976.It is a genuine pleasure for the author to thank D. N. Nasledov and O. V. Emel'yanenko for interest and attention they have accorded this work, and R. K. Rad for supplying the gallium phosphide samples.     

Photoconductive response of GaAs epitaxial layers

In the present work the photoconductive response of low resistivity, n-type GaAs epitaxial layers is studied by experimentally monitoring the dependence of the photoconductive gain (PG) optoelectronic parameter upon incident photon flux and temperature. The characterized samples fall into three major categories: ion implanted (II) GaAs epilayers formed within undoped, semi-insulating GaAs substrates; GaAs epitaxial layers grown by liquid phase epitaxy (LPE) on Cr-doped, semi-insulating GaAs substrates; and ungated GaAs MESFETs.     

Electron and impurity distributions in epitaxial n-type gallium arsenide

The electron, donor, and acceptor distributions along the thickness of epitaxial gallium arsenide films were studied as functions of the nature and orientation of the substrate. There is a discussion of mechanisms which may be responsible for these distributions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 96–100, January, 1971.     

Electrophysical characteristics of accidental-doping defects in epitaxial n-type gallium arsenide

The Hall effect and electrical conductivity in the temperature range 10–900?K were used to investigate the electrophysical parameters of accidental defects in epitaxial n-type gallium arsenide. The experimentally determined parameters of the shallow donor impurity found in n-type gallium arsenide are similar to those of silicon. The anomalous behavior of the Hall constant at T>500?K can be accounted for by the hypothesis of thermal conversion of oxygen-containing defects (complexes of intrinsic and extrinsic defects) from a neutral state to an electrically active state. The kinetic parameters of this process are evaluated. The deviation of the experimental behavior of the electron mobility at temperature above 500?K can be attributed largely to the nonuniformity of the electrophysical parameters over the thickness of the gallium arsenide films and to the presence of accidental oxygen-containing defects in the investigated material.     

Hopping conduction in epitaxial n-GaAs layers

The conductivity results of the phonon-assisted hopping process in n-type GaAs at low temperatures are presented. The conductivity variation with T, N_D and H are analyzed in terms of the percolation theory results.     

Ohmic contacts to GaAs epitaxial layers

Formation of ohmic contacts onto GaAs epitaxial layers was reviewed. Because the Fermi energy of GaAs is pinned at the surface near the middle of the bandgap, it is impossible to choose a metal with the proper work function to make an ohmic contact. Instead, it is necessary to create a heavily doped surface layer and using field emission or thermionic field emission to achieve an ohmic contact. The oldest known contact metallization for GaAs is sequentially deposited thin films of Au, Ge, and Ni. It was shown that the ‘dopant diffusion model’, widely accepted to date to explain the formation of an n⁺ layer on GaAs to form the ohmic contact, is incorrect. Instead, the “solid phase regrowth model” was discussed in detail and shown to describe formation of ohmic contacts in this system. Based on this result, general rules for forming ohmic contacts to compound semiconductors with pinned Fermi levels or large values of electron affinities plus bandgap were expressed.     

Suppression of intermixing in strain-relaxed epitaxial layers

Misfit strain plays a crucial role in semiconductor heteroepitaxy, driving alloy intermixing or the introduction of dislocations. Here we predict a strong coupling between these two modes of strain relaxation, with unexpected consequences. Specifically, strain relaxation by dislocations can suppress intermixing between the heterolayer and the substrate. Monte Carlo simulations and continuum modeling show that the suppression, though not absolute, can be surprisingly large, even at high temperatures. The effect is strongest for a large misfit (e.g., InAs on GaAs) or for thin substrates (e.g., Ge on silicon on insulator).     

Interdiffusion of layers in PbSe-PbS epitaxial superlattices

X-ray diffraction methods are used to investigate the diffusional mixing of layers in PbSe-PbS superlattices. The interdiffusion coefficients of the layers are determined from the change in the intensity of satellite reflections. Two stages of diffusion are observed — fast (at the initial stages of anneals) and slow. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 9, 685–687 (10 November 1998)     

Impurity photoconductivity in epitaxial layers of gallium arsenide

Impurity photoconductivity spectra in the range 0.5–1.5 eV are studied in epitaxial layers of n-GaAs grown on substrates of semiconductive GaAs withρ > 10⁶ Ω·cm in the system Ga-AsCl₃ -H₂. The effect of uncontrolled acceptor impurities on the impurity photoconductivity spectrum is evaluated.     

Growth of gallium nitride epitaxial layers and applications

The lack of appropriate substrates has delayed the realisation of devices based on IIInitrides. Currently, the heteroepitaxial growth of GaN by metal organic vapour phase epitaxy (MOVPE) produces GaN layers which, despite huge densities of dislocations, allow the fabrication of highly efficient optoelectronic devices. Henceforth, a new technology in heteroepitaxy of GaN, the epitaxial lateral overgrowth (ELO) has produced GaN layers in which the density of dislocations has been reduced by several orders of magnitude. With the ELO, nitride based laser diodes (LDs) working at room temperature in cw mode with a lifetime of 10,000 hours have been demonstrated by Nichia. In addition to LDs, IIInitrides presently offer a wide range of applications in optoelectronics (high brightness light emitting diodes (LEDs), from amber to UV, solar blind detectors); in electronics, high temperature/high power field effect transistors (FETs). The development of molecular beam epitaxy (MBE) of nitrides has been hindered during several years by the lack of an efficient nitrogen source. This problem being solved, MBE has recently demonstrated state-of-theart quantum well and quantum dot heterostructures, and 2D electron gas heterostructures.     

Conductivity peculiarities in epitaxial layers of cadmium selenide

Electrophysical properties are studied in epitaxial cadmium selenide films produced by condensation on common mica and fluorophlogopite substrates over a wide range of substrate temperatures (T_s). It is shown that under conditions close to equilibrium highly perfect layers are produced with charge carrier mobility up to 300 cm²/V · sec and concentration ～ 10¹⁶ cm^?3. The temperature dependence of carrier concentration and mobility are studied in undoped and doped CdSe films. The values of the intercrystallite energy barriers are determined in layers condensed at differing T_s. It is shown that at T_s>630?C the charge carrier diffusion mechanism is close to that of a monocrystal, while for a barrier diffusion mechansim (T_s<630?C) the character of the energy barriers for the cubic and hexagonal phases in CdSe is somewhat different. Donor-level ionization energy and ionized center concentration are determined.