Electron scattering and transport phenomena in small-gap zinc-blende semiconductors

We give expressions for electrical conductivity, thermoelectric power and thermal conductivity of conduction band electrons in small-gap zinc-blende semiconductors, obtained by solving the Boltzmann equation by a variational procedure. The term resulting from the phonon-drag is included in the Boltzmann equation. The following electron scattering mechanisms are investigated: inter and intraband scattering by optical phonons via polar and nonpolar interactions, scattering by charged centers (ionized defects and heavy holes) and by neutral centers, as well as scattering by acoustic phonons. Particular attention is paid to the screening of the electron-optical phonon polar interaction by free carriers, which is particularly important in the case of a linear energy band. The formula for the intraband RPA dielectric function for the case of the linear band is given.The general formulation of all the problems investigated permits direct application of the results given in this paper to both intrinsic or n-type HgTe-type and InSb-type semiconductors, including mixed crystals, e.g. Cd_xHg_1?xSe near the cross point.     

Electron transport in disordered semiconductors

The density matrix of an electron in an amorphous semiconductor, written as a double path integral, is averaged over random disorder. For small disorder the golden rule result is recovered. When the mean disorder energy approaches k_BT, the electronic mobility goes to zero signalling disorder induced localization.     

Resonant spin-optic-phonon interaction in small-gap semiconductors

Coupling of electron spin to optic phonons due to spin—orbit interaction is studied theoretically for small-gap semiconductors in the presence of a magnetic field. We predict an anomalous behaviour of magnetic levels when spin-flip energies become equal to the phonon energy. The effects should be observable in HgTe-type materials.     

Subband states inn-inversion layers on small-gap semiconductors

Subband states inn-inversion layers on small-gap semiconductors are subject to the coupling between valence and conduction band (nonparabolicity effects). In order to account for this coupling we study different models: two of them are based on Kane's 6×6 and 8×8 bulk-Hamiltonians, the third one takes into account higher order terms of the electron momentum in a 2×2 conduction band Hamiltonian. We perform selfconsistent calculations for these models with parameters characteristic for InSb and HgCdTe and electron concentrationsN _S , for which up to two subbands are occupied. The calculated subband separations and Fermi energies are independent of the models only if the same energy band dispersion is used and depend strongly on the applied boundary conditions.Work supported in part by the Deutsche Forschungsgemeinschaft     

Electron transport in II–VI compound semiconductors

The mobility characteristics of II–VI compound semiconductors have been investigated using a displaced Maxwellian model for the energy distribution of the free carriers and considering the combined effects of acoustic, piezo-electric, ionised impurity and polar optical modes of scattering. The electric field dependence of the carrier mobility has been obtained at lattice temperatures of 77° K and 300°K. The effect of variation of the not too well known coupling constants on the characteristics has been observed. The variation of the low-field mobility with the lattice temperature and with the level of impurity concentration has also been obtained. The theoretical results agree quite satisfactorily with the available experimental data and with other theoretical works.     

Anisotropy of transport phenomena in semiconductors of the tetragonal system

An investigation is made into the anisotropy of transport phenomena in semiconductors of the tetragonal system in classical magnetic fields with arbitrary orientation and magnitude. A detailed study is made of the anisotropy of the transport coefficients in the region of weak magnetic fields. A condition is obtained under which semiconductors with anisotropic conductivity are characterized by an isotropic Hall coefficient. It is established that the transport coefficients have qualitatively different asymptotic behaviors in strong magnetic fields of different orientations. The obtained expressions are general in nature and apply to a large class of semiconductors.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 69–74, August, 1980.     

New transport phenomena in variable gap semiconductors and their device applications

This article reviews recent work on electron transport in graded gap semiconductors. Many new applications are also discussed such as staircase devices, heterojunction bilopar transistors and sawtooth superlattices.     

Electron transport in semiconductors in the presence of impact ionization

The development of impact ionization in semiconductors has been considered. A transport equation for the electron distribution function in the presence of impact ionization has been derived. It has been found that the collison integral of this equation is nonlinear with respect to the distribution function. The relation between the solutions of this equation and the usual Boltzmann equation have been determined. A Monte Carlo method for numerical calculations in the presence of impact ionization has been developed. The results of numerical calculations carried out using a simplified model of indium antimonide are presented.     

High-field cooperative transport phenomena and screening in phase-separated degenerate antiferromagnetic semiconductors

Response to a strong electric field is investigated of degenerate antiferromagnetic semiconductors EuTe spontaneously separated into antiferromagnetic and ferromagnetic phases. Whereas in weak fields their response is Ohmic, in strong fields a sequence of very high peaks appears over the Ohmic-type background beginning from a certain threshold field strength. Their spacing decreases with increasing field strength. These peaks are explained by cooperative motion of charged ferromagnetic microregions inside the antiferromagnetic host. The screening by these microregions is investigated theoretically.     

A simple morphogenetic reaction-diffusion model describing nonlinear transport phenomena in semiconductors

Originally designed to account for the main phenomena of symmetry-breaking morphogenesis, the well-known Rashevsky-Turing theory is a prototype model of many different synergetic systems in nature. The simplest version of Turing's model can be realized by a two-cellular symmetrical reaction-diffusion system, consisting of two cross-inhibitorily coupled, potentially oscillating two-variable subsystems (4-D flow). We present numerical evidence of symmetry-breaking nonequilibrium phase transitions from phase-locked coherent to phase-lagged differentiated behavior of the two subsystems. We further investigate the structural change of the system flow from stable morphogenesis to boiling-type turbulence. Finally, we present experimental evidence that the spatiotemporal nonlinear behavior of impurity-impact-ionization-induced avalanche breakdown in semiconducting germanium can be described qualitatively by the present 4-D reaction-diffusion model.     

Mid-infrared nonlinear phenomena in polycrystalline semiconductors

We have studied second-harmonic generation by 30 ps and 70 ns 10 m CO₂ laser pulses in nonlinear polycrystalline ZnSe, CdTe and GaAs samples. Second-harmonic generation in these materials can limit the amplification of high-power CO₂-laser pulses in amplifier chains sealed with these polycrystalline IR-transmission materials. On the other hand, we now demonstrate for the first time that these materials are suited as nonliner elements for autocorrelation measurements on short infrared laser pulses. For such pulse-width measurements polycrystalline materials have an advantage over single crystals, e.g. GaAs, because they are insensitive to misalignement. Furthermore, these polycrystalline optical elements are easier and cheaper to manufacture than single crystal devices. With such polycrystalline materials we were able to realize reliable autocorrelation measurements of 30–300 ps 10 m optical-free-induction-decay (OFID) laser pulses.     

Laser-induced synergetic phenomena in impure semiconductors

It is shown that the energy flux due to a laser light passing through a disordered system represented by a semiconductor with impurities causes the self-organization of new ordered states and gives rise to physical phenomena typical of synergetics generally described byHaken. The properties of these ordered states remind one distantly of those of ordinary superconductors and pure crystals. Theoretical explanations of the observed phenomena concerning the optical stopping effect and the light-induced transmittance oscillations in thin films are given. New sorts of the phase transitions of the first order and the electron diffraction on disordered systems illuminated by a laser light are predicted.The author is very much indebted to Dr. . Bárta for stimulating discussions and for his information on the experimental existence of the light-induced transmittance oscillations in thin film.     

Electron propagation in magnetic semiconductors

A simple decoupling scheme is suggested and analyzed for the problem of the electron propagation in magnetic semiconductors treated in the s-d model. In most important cases, the method is shown to reduce to the Kubo form of the coherent potential approximation. It is then used to assess the role of higher order effects in the red shift of the optical absorption edge.     

Electron states in diluted magnetic semiconductors

One of the remarkable properties of the II–VI diluted magnetic semiconductor (DMS) quantum dot (QD) is the giant Zeeman splitting of the carrier states under application of a magnetic field. This splitting reveals strong exchange interaction between the magnetic ion moment and electronic spins in the QD. A theoretical study of the electron spectrum and of its relaxation to the ground state via the emission of a longitudinal optical (LO) phonon, in a CdSe/ZnMnSe self-assembled quantum dot, is proposed in this work. Numerical calculations showed that the strength of this interaction increases as a function of the magnetic field to become more than 30 meV and allows some level crossings. We have also shown that the electron is more localized in this DMS QD and its relaxation to the ground state via the emission of one LO phonon is allowed.     

Electron capture cross-section in covalent semiconductors

The energy dependence of the differential capture cross-section for the free carriers in a covalent semiconductor is obtained by a numerical method adopting the Abakumov-Yassievich model [1] for the process of recombination. The result is essentially required for a theoretical study of the electrical transport and other related phenomena in semiconductors at low lattice temperatures.