Infrared absorption in gallium arsenide,produced by deep defect levels

When GaAs is irradiated by protons and rapid neutrons there appears a significant supplementary absorption beyond the long-wave edge of the basic band, produced bythe presence of deep defect levels in the irradiated specimens [1, 2], Until recently it was assumed that irradiation of gallium arsenide by electrons produced insignificant changes in the absorption spectrum [2]. However, a later study of the absorption spectra of specimens irradiated by electrons with E =1.5 MeV found an optical absorption band in the region of 1.0 eV [3].     

Kinetics and growth mechanism of gallium arsenide crystals in gas-phase epitaxy

Conclusion In conclusion, we note that gallium arsenide itself is the material with which the physicochemical and crystallophysical fundamentals of gas-phase epitaxy are presently being developed. It is hoped that the basic principles or crystal growth in gas-phase systems discovered in gallium arsenide will prove sufficiently general to be applied to other analogous systems.The complex multistage processes occurring on a crystal surface during gas-phase crystallization require development of a more general theory of crystal growth — one which considers heterogeneous reactions and participation in the surface processes of noncrystallizing atoms and molecules. On the other hand, for construction of such a theory and its comparison to experiment information will be required not only on the composition of the gaseous phase and the growth kinetics, but also on the composition and structure of the adsorption layer and the crystallization surface, the acquisition of which in gas-phase systems is complicated in comparison to, for example, molecular-beam epitaxy systems. It is possible that these difficulties will be overcome with time. A certain part of the information on composition and structure of the surface in contact with the complex gas phase can apparently be obtained under conditions close to equilibrium. This part of the problem of gas-phase epitaxy research merges completely with problems of the characterization of the physicochemical state of semiconductor surfaces in general.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 23–37, January, 1980.     

Impurity vibrations of copper defect complexes in gallium arsenide crystals

Dynamical properties of several copper defect complexes in GaAs are studied. The complexes studied include models for the C and F centers recently investigated experimentally by Gross, Safarov, Sedov, and Marushchak. It is shown that these models are capable of giving rise to resonance modes whose frequencies agree with the positions of peaks in the optical spectra of these defect complexes, when reasonable changes in the force constants coupling the substitutional copper impurities to the host crystal are included in the dynamical models. In addition the vibronic and infrared absorption spectra of these complexes have been calculated.     

Ultraviolet photoemission from polymeric sulfur nitride polycrystalline films and single crystals

The (SN)_x valence band structure, for polycrystalline films as well as for single crystal samples, has been studied using He I and He II resonance radiation. In angle-resolved photoemission energy distributions from single crystals, structure in the spectra is selectively enhanced offering a possibility of assigning the photoemission as originating from particular regions of the Brillouin Zone. The observed onset of photoemission 0.2 eV below the Fermi edge is discussed.     

Effect of gettering on the atomic structure of gallium arsenide

No changes in the lattice constant or standard parameters due to statistical displacements of atoms from their ideal positions at room temperature are revealed during a study of the atomic structure of gallium arsenide crystals gettered by yttrium. Nonetheless, the effect observed for conventional, ungettered crystals and associated with the influence of point defects on the phonon spectrum disappears.     

The photoelectric properties of polycrystalline films of gallium arsenide

Certain photoelectric properties of polycrystalline films of gallium arsenide at room temperature obtained by a gas deposition method are studied. It is found that film specimens of GaAs have much greater photosensitivity than the solid material for the same current carrier density.The barrier theory of conductivity is invoked in order to explain the relationships observed.     

Superconductivity of niobium nitride single crystals after implantation of carbon and nitrogen

Single crystals of δ-NbN_0.85 with a superconducting transition temperature T_c of 14.3 K were implanted with nitrogen and carbon ions at room temperature and subsequently annealed at high temperatures. Implantation was also performed at high substrate temperatures. After implantation at about 920°C maximum T_c-values of 16.5 and 17.8 K were obtained with N- and C-ions respectively. Disorder observed after room temperature implantation consisted of displaced Nb-atoms which could not be completely annealed in an isochromous annealing process up to 1000°C. For annealing temperatures above 1100°C nitrogen diffusion out of the implanted layers resulted in a reduction of T_c.     

Properties of n-type gallium arsenide doped with germanium when single crystals are grown from the melt

The temperature dependences of the density, mobility, and lifetime of electrons, and the photoconductivity and cathodoluminescence spectra of gallium arsenide with different electron densities doped with germanium when single crystals are grown by the Czochralski method are investigated. An analysis of the scattering mechanism is given, and the acceptor and donor densities are determined. The acceptor-type capture levels are found from the temperature dependence of the electron lifetime. The results of a study of the cathodoluminescence spectra indicate the presence in the specimens of complex radiational recombination centers similar to germanium-atom complexes with inherent lattice defects.     

Magnetostructural phase transitions in manganese arsenide single crystals

The effect of an external magnetic field with a strength up to 140 kOe on the phase transitions in manganese arsenide single crystals has been investigated. The existence of unstable magnetic and crystal structures at temperatures above the Curie temperature T _C = 308 K has been established. The displacements of manganese and arsenic atoms during the magnetostructural phase transition and the shift in the temperature of the first-order magnetostructural phase transition in a magnetic field have been determined. It has been shown that the magnetocaloric effect in a magnetic field of 140 kOe near the Curie temperature T _C is equal to ??T ?? 13 K. A model of the superparamagnetic state in MnAs above the temperature T _C has been proposed using the data on the magnetic properties and structural transformation in the region of the first-order magnetostructural phase transition. It has been demonstrated that, at temperatures close to T _C, apart from the contribution to the change in the entropy from the change in the magnetization there is a significant contribution from the transformation of the crystal lattice due to the magnetostructural phase transition.     

Parameters of thulium-doped gallium nitride crystals with wurtzite structure

A study was made of GaN crystals grown by HVPE and MOCVD. Thulium was introduced by diffusion. It is shown that the Tm rare-earth ion acts as an acceptor in a GaN semiconductor matrix if the undoped crystal contains deep-level defects. Intracenter f-f transitions characteristic of Tm were observed in the short-and long-wavelength spectral regions. The short-wavelength emission intensity is higher in crystals obtained by MOCVD.     

Structural and optical studies of thin films of aluminum nitride grown via ion-plasma sputtering on gallium arsenide substrates with different orientations

IR and UV spectroscopy is used to study the properties of nanostructured aluminum nitride films obtained via reactive ion-plasma sputtering on GaAs substrates with different orientations. Nanostructured thin (100–200 nm) films of cubic aluminum nitride with optical bandgaps of ~5 eV and refractive indices varying from 1.6 to 4.0 in the wavelength range of ~250 nm are fabricated. Growth on a misoriented GaAs(100) substrate (4° with respect to the [110] plane) makes it possible to synthesize AlN films with smaller grains and higher refractive indices (n ~ 4). It is shown that misoriented GaAs substrates allow us to control the morphology, surface composition, and optical functional characteristics of AlN/GaAs heterophase systems.     

Formation of gallium microinclusions in GaAs single crystals

In this report we analyze the causes of gallium microinclusion formation in gallium arsenide single crystals. We present a model in which microinclusions result from the decomposition of a supersaturated solid solution. From experimental data available in the literature and calculated kinetic parameters of the model we demonstrate that microinclusion formation in bulk single crystals follows the mechanism of homogeneous nucleation and Brownian coalescence of precipitated liquid gallium metal.Translated from Izvestiya Vysshikh Uchbenykh Zavedenii, Fizika, No. 2, pp. 32–35, February, 1988.