Diamagnetism of narrow-gap semiconductors

Computations are performed of the diamagnetic susceptibility of a degenerate electron gas in narrow-gap semiconductors. The structure of the diamagnetic contribution is analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 71–74, February, 1987.     

Recombination in narrow-gap semiconductors

This review is intended to be an introduction to the recombination mechanisms important for narrow-gap semiconductors. The study of recombination mechanisms gives information on the various interactions the free carriers happen to meet in crystals. On the other hand recombination mechanisms are limiting the performance of all the modern solid state electronic devices. It was recently observed that the dominant recombination processes in narrow-gap semiconductors are different from those important for the classical semiconductors. Due to the narrow band gap the intrinsic carrier density is rather large and in addition the band gap energy is of the same order of magnitude as the energy of elementary excitations as LO-phonons or plasmons, and typical cyclotron-resonance energies. Accordingly processes as the Auger effect or recombination by emitting single phonons or single plasmons become highly probable. These mechanisms have been observed recently and also a new magnetic quantum effect was discovered. The new processes have proved to be important for devices like infrared detectors and infrared solid state lasers, but revealed also some fundamental properties of semiconductors.     

Calculation of geometries and chemisorption energies of adatoms on simple metals

We report results of calculations with a formalism that in principle applies quite generally for chemisorption on a real metallic substrate. Including the substrate structure within perturbation theory on a self-consistent jellium-plus-adatom calculation, we have computed the dependence of the binding energy of an adatom on the surface geometry. Specifically, in the case of hydrogen on Al, our model calculation predicts that the stable positions are bridge configurations on the (100) and (110) surfaces and atop positions on the (111) surface, and that they have almost the same heats of chemisorption (1.8–2.0 eV). For geometrical reasons the bridge configuration seems to be a reasonable result while the atop result for the (111) surface is more uncertain. Thus, chemisorption of H on Al should require predissociation of the H₂ gas. In addition, the predicted values for hydrogen desorption imply that measurements on H on Al surfaces should be performed at low temperatures to avoid desorption. Results for H on a jellium of Na density indicates that hydrogen should be absorbed in rather than adsorbed on Na metal.     

Auger recombination in diamond-like narrow-gap semiconductors

In the calculation of the transition rate of Auger recombination in the Kane model the overlap integral between the wave functions of the conduction and heavy hole bands is equal to zero at the threshold. As a result the preexponential function has a different temperature dependence in comparison with the case of simple parabolic bands. The theoretical value of the recombination lifetime is in agreement with experimental data for InSb at 300 K. Estimates of the overlap integral given earlier are analyzed.     

Quantum well based on graphene and narrow-gap semiconductors

The energy spectrum of a planar quantum well formed by two narrow-gap semiconductor strips with a graphene strip inserted between them was considered. It was shown that the gapless mode arises only in the case of inverted narrow-gap semiconductors. Taking into account the graphene specificity, the spin splitting of the energy spectrum of the asymmetric quantum well was calculated. Interface states and optical transitions were studied. It was shown that optical transitions are possible only with parity conservation.     

Far infrared reflection spectra in narrow-gap semiconductors

Far infrared reflection spectra of Cd_XHg_1–X Se are measured in the region 20 to 600 cm^–1 at temperatures between 5 and 77 K. Reflection spectra are explained well by the dynamic dielectric function which is constructed as a sum of ₈–₈ interband, intraband and phonon contributions. The plasmon-LO phonon coupling effect is also discussed.     

Impurity states in narrow-gap and gapless semiconductors

The influence of interband interactions on the location of impurity stages in narrow-gap and gapless semiconductors of A^IVB^VI type is considered in the T-matrix approximation. It is shown that taking account of the interband interaction results in diminution of the activation energy of the impurity level.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 108–111, January, 1977.The authors are grateful to B. L. Gel'mont for discussing the research and the remarks made.     

Drag of carriers by photons in narrow-gap semiconductors

The current representing the drag of carriers by photons is calculated for cubic narrow-gap semiconductors allowing for the nonparabolicity and nonsphericity of the valence subbands. A quantitative Kane model is used to obtain a general tensor expression for the photocurrent related to the coefficients representing the nonparabolicity of the light-hole subband and the nonsphericity of the heavy-hole subband. The results are given of a numerical calculation of the principal parameters of the drag current in the form of components of the elementary tensors (as a function of temperature) and of the coefficient representing the nonparabolicity (as a function of the wavelength of the incident light) in the case of narrow-gap Hg_1–xCd_xTe solid solutions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 62–66, May, 1980.     

Convection in the bridgman growth of narrow-gap semiconductors

Summary The free convection in the melt during the crystal growth of small-gap semiconductors, and its influence on the electrical properties are discussed. Dimensionaless parameters of the fluid flow, electrical properties of PbTe, Pb_1−x Sn _x Te and Hg_1−x Cd _x Te single crystals, grown by vertical Bridgman technique at very low velocity, and some structures, found in these materials, support the presence of free convection.     

Theory of temperature-dependent knight shift in narrow-gap semiconductors

We derive a theory of the temperature-dependent Knight shift in narrow-gap semiconductors. As an example, we calculate the temperature variation of the Knight shift of ²⁰⁷Pb in p-PbTe, which agrees fairly well with experiment.     

On the mechanism of chemisorption on magnetic semiconductors

A mechanism of chemisorption on magnetic semiconductors is considered at T = 0. The adatoms behave with respect to the electronic spectrum of a crystal as surface donors. Interaction of the valence electron of the atom with the spins of the crystal (s-d interaction) results in the formation of a ferromagnetic microregion in the vicinity of the adsorbed atom. The one- and two-electron bond of the adatom with the crystal is considered. The tendency for the adatom ferromagnetic regions to merge results in an effective attraction between the adatoms; moreover many adatoms can attract each other simultaneously.     

Temperature and pressure behaviour of narrow-gap semiconductors including galena

The structural high pressure and temperature investigation of narrow-gap semiconductors (lead chalcogenides) has been performed in the present article. A realistic approach for room temperature and high temperature study of narrow-gap semiconductors has been used. It is examined that the present compounds are more stable in NaCl-phase and they transform to CsCl-phase at high pressure. In the present article, the phase transition pressures and volume collapses of lead chalcogenides have been investigated at room and high temperatures. Phase transition pressures have been reported at high temperature range from 0 to 1200 K. Elastic and anharmonic constants have also been reported at room temperature. A structural study of the narrow-gap semiconductors have been carried out using the realistic model including temperature effect. The temperature and pressure behaviour of elastic constants for the present compounds have also been discussed. Furthermore, various mechanical and thermo dynamical properties like modulus of elasticity, Debye temperatures etc. are also presented.     

Problem of impurity states in narrow-gap lead telluride-based semiconductors

A review of recent results of experimental investigations devoted to studying unusual properties of impurity states in doped narrow-gap lead telluride-based semiconductors is presented. These results are analyzed in the framework of existing theoretical concepts.     

Theory of magnetic susceptibility of semimetals and narrow-gap semiconductors

We calculate the magnetic susceptibility of PbTe as an example to show that semimetals and narrow-gap semiconductors with large effective g-factors are highly diamagnetic.     

Calculation of I–V curves in narrow-gap semiconductors with symmetric electron and hole energy dispersion laws

The hot electron phenomena are considered in the narrow-gap semiconductors with Lax band structure. Methods for calculation of I–V curves are developed in the case when only the quasielastic scattering processes occur. The following factors are taken into consideration: Bloch structure of wave functions; electron-electron interaction; change in concentration of carriers due to the warming of electrons in the electric field; anisotropy and many-valley character of band spectrum. Results obtained here may be useful for the interpretation of experimental data for alloys Bi_1-xSb_x, lead and tin chalcogenides.     

Spin splitting in narrow-gap Pb1−xSnxTe semiconductors

The g factor in the solid solutions Pb_1–xSn_xTe of the p and n type (x = 0, 0.1, 0.19, 0.2, 0.28, and 0.38), doped with germanium, cadmium, and bismuth, is determined from investigations of the quantum oscillations of the magnetoresistance. Comparison of the results obtained with theoretical calculations, taking into account the dependence of the matrix element of the momentum operator on the composition x, shows that the experiment agrees well with the theory within the framework of Dimmok's model. Analysis of the experimental results indicate that doping with nonmagnetic impurities does not affect the magnitude of the spin splitting.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 78–83, August, 1987.We are grateful to Doctor of Physical-Mathematical Sciences K. D. Tovstyuk and Candidate of Physical-Mathematical Sciences V. B. Orletskii for providing the possibility of formulating and successfully carrying out these studies, their constant interest in this work, and for valuable discussions of the results.     

Auger transitions in narrow-gap semiconductors with lax band structure

Auger recombination and ionisation rates are calculated in narrow-gap semiconductor with Lax band structure⁸ such as Pb_1?xSn_xTe, Pb_1?xSn_xSe, Bi_1?xSb_x. Both low-energy (T_e? ε_g) and high-energy (ε_F ? ε_g or Te ? ε) regions are taken into consideration. In the former case we have corrected the results obtained by number of authors^3,4. The latter situation may take place in pinch channel or at the high level of laser exitation. Here we have derived the results except for constant numerical coefficient. We consider the two-particle Auger-process proposed by Emtage³ as well as three-particle ones including additional collision with acoustical phonon, charged impurity or neutral defect. The dependence of Auger transition rates upon the carrier concentration is mainly of the power-type in all variants.