An investigation was made of the characteristics of different silicon carbide photodetectors: 1) with a Schottky barriers; 2) with a p-n junction, made by epitaxy diffusion of aluminum and boron; 3) avalanche photodiodes. These photodetectors had a high efficiency in the ultraviolet part of the spectrum with a sensitivity maximum at 250-330 nm and they were capable of operation at temperatures of 500-degrees-C.
An investigation was made of the Raman scattering in TlGaS2 crystals, which were oriented in different geometries, and of the temperature dependences of such scattering at 77-400 K. A phase transition was found: it altered the polarization dependences of the vibrational modes, caused line splitting, weakened some and enhanced other vibrational modes when temperature was lowered. An investigation was made of the vibrational reflection spectra in the range 4000-50 cm-1. Polar vibrational LO and TO modes as well as their principal parameters were identified. A calculation was made of the effective Szigeti charge, of the dynamic Born charge, and of the relative effective charge of the anions and cations using the data obtained from the E parallel-to a and E parallel-to b polarizations in TlGaS2 crystals. It was found that the ionicity of the cations and anions was different along the a and b axes.
The Auger and mass spectroscopy methods were used in studies of the surfaces of II-V samples subjected to different treatments. A technology was developed for preparing atomically clean surfaces. The spectral distributions of the photoemission, lambda-modulated photoemission, absorption, reflection, lambda-modulated absorption, and photoresponse of surface-barrier diodes were determined. A comparison was made of the results with one another and with the known theoretical calculations. An analysis of the structure of the energy bands of II-V compounds was carried out in the region of the minimum of the gap between these bands. The first attempts were made to fabricate photoemitters with a negative electron affinity from ZnAs2 and CdP4. The feasibility of constructing polarization-sensitive and narrow-band photoemitters was demonstrated.
An investigation of heterostructures belonging to the InAs/InAsSbP system revealed a crossover from heterostructures of the first to those of the second type. A phase diagram of the states of heterojunctions in this system was plotted: it showed the regions where the structures of the first and second types were observed, as a function of the composition of the quaternary solid solution. A study of the photoluminescence confirmed the existence of the two types of heterostructure. Stimulated emission from the heterojunction of the second type was observed.
A phenomenological theory of the correlation recombination mechanism is proposed. In contrast to the Shockley-Read model, a recombination center is regarded as a two-level system in which the position of the lower hole level depends on the population of the upper electron level. This mechanism accounts for the large hole-capture cross section of an A center (representing a radiation defect with a level at E(c) - 0.17 eV) in the course of multiphonon carrier recombination. An account is given also of the appearance of a narrow luminescence line representing an internal transition between two bound states in an A center.
A review is given of the main properties of a new class of two-dimensional electron systems, which are structures containing a monolayer of a dopant (known as a delta layer). A self-consistent theory is considered: it makes it possible to calculate the energy spectrum of a structure, as well as the carrier densities and mobilities in the individual size-quantization subbands, including those in the case when an additional gate electrode is present. The results of experimental studies of galvanomagnetic, optical, and other properties and of the luminescence of delta layers are reported and discussed. Potential applications of such layers in field-effect transitions are considered.
An investigation was made of the bulk and surface characteristics of n-type Hg1-xCdxTe (x = 0.02) solid solutions at temperatures in the range 0.5 < T < 50 K. The magnetic-field dependences of the Hall coefficient and of the magnetoresistance were determined in the region of a metal-insulator transition using samples with different carrier densities and magnetic fields up to 2.5 T. An analysis was made of the temperature dependences of the electron density n(s) and mobility mu(s) in a surface layer ai the frequency f = 130 GHz.
Photoelectric measurements (at helium temperatures and galvanomagnetic measurements at 4.2-300 K) were made on a batch of (Pb1-xSnx)0.99In0.01Te (0.3 < x < 1) single crystals. The samples with x = 0.31, 0.35, and 0.40 exhibited slow relaxation of nonequilibrium carriers at T < 20 K. In the case of the sample with x = 0.6 there was no such slow relaxation, but the kinetic characteristics indicated a weak influence of indium on the scattering process. In a sample of Sn0.99In0.01Te the scattering by indium atoms became the dominant effect at low temperatures. The dependence of the level of stabilization of the chemical potential on the composition was determined.
An investigation was made of undoped and Sb-doped ZnP2-D48 crystals. The conventional and wavelength modulation spectra were recorded at 77 K, the luminescence spectrum was studied at 2 K, and the temperature dependences of the luminescence were determined. Indirect phonon-assisted transitions to different (B0, C0, and D0) bound exciton states occurred at the same energies. The spectra were superimposed on one another forming a complex line structure and giving rise to a global absorption profile of the kind encountered in interference spectra. A good agreement was observed between the phonon energies and the energies of vibrational modes participating in the Raman scattering processes, i.e., of the GAMMA-phonons, demonstrating that an extremum of the valence band was located near the point k = 0 of the Brillouin zone.
An investigation was made of the current-voltage and capacitance-voltage characteristies of p+-Si*-SiO2-p-Si structures with the insulator thickness less than 50 angstrom. The initial surface band bending in p -type silicon was phi(s)0 = 640-720 mV for oxide thicknesses from 20 to 33 angstrom. The current-voltage characteristics recorded under forward bias voltages exceeding the surface band bending of p-type Si had a very definite threshold, which was due to conversion of the Si-S2O2 interface to a state of accumulation of majority carriers (holes). The current was governed by the tunneling of the majority carriers from such a p-type accumulation layer across the oxide to the p+-type polycrystalline silicon layer. The nature of the fall of the forward current on increase in the oxide layer thickness indicated that the structure of the oxide layers 20-33 angstrom thick differed from that of stoichiometric SiO2.
A method based on the transfer matrix is used to relate the solutions of the Schrodinger equation in regions with zero values of the potential. It is shown that the transfer matrix is governed by six parameters: the de Broglie wavelength corresponding to a free particle, the coordinates of the left- and right-hand boundaries of a potential barrier (across which the solution is "transferred"), the transmission coefficient, and the phase characteristics of the transmitted and reflected waves. The last three nontrivial parameters are calculated using recurrence relations. The expressions necessary for the investigation of potential barriers with a step on the right are also obtained. The proposed method making it possible to study resonant tunneling in one-dimensional quantum systems, for which the potential and the effective mass of a particle can be represented by piecewise-continuous functions of the spatial variable.
Resonant tunnel diodes with spacer layers and with a lightly doped buffer layer were made. The current-voltage characteristics measured at 77 and 300 K had singularities in the negative differential conductance region. These singularities were attributed to the flow of the current involving size-quantization levels in the potential well of a spacer layer and not due to self-excitation. The solution of a self-consistent system of the Schrodinger and Poisson equations yielded the dependences of the depth of the potential well and of the energy levels in the well on the voltage applied to a diode. It was found that the maxima of the current in the characteristics occurred when the resonant level coincided with the bottom of the conduction band or with the size-quantization levels.
Prolonged storage of Au-p-InP Schottky diodes in air induced a structural transition Au-p-InP --> Au-n-In2O3-p-InP. An investigation of the current-voltage characteristics of such heterostructures revealed that the current flow mechanism was governed by the tunneling of carriers via trapping states. The photoresponse of these heterostructures could be represented analytically by I(ph), is-proportional-to (hnu - E(m))m, where E(m) = 1.4-1.6 eV and m = 3, and it was governed by the internal photoemission from p-type InP into n-type In2O3.
