E. M. Sheregii

Far-infrared reflectivity as a probe of point defects in Zn- and Cd-doped HgTe

We present a nondestructive method for quantitative determination of the vacancy concentration in the lattice of Hg-based semiconductor alloys with tetrahedral structure. The method is based on the identification of additional vibrational modes (AVMs) induced by lattice deformations in the far-infrared (FIR) reflectivity spectrum. Although the method is restricted by sensitivity limitations, recent FIR experimental data carried out on HgZnTe and HgCdTe samples containing Hg vacancies confirmed the presence of AVMs induced by Hg vacancies in as-grown crystals.

Phonon and vibrational spectra of hydrogenated CdTe

This work presents far-infrared reflectivity spectra collected with synchrotron radiation on specially prepared CdTe monocrystals in the temperature region of 30–300K. The investigated samples were of three different types characterized by the three different levels of hydrogenation—strong, middle, and low ones. In order to interpret the experimental data, the imaginary part of the dielectric function was evaluated by means of Kramers-Kronig transformation. To determine quantitatively the influence of hydrogen atoms on the phonon and vibrational spectra of hydrogenated CdTe crystals we used the special statistical model proposed in this paper. This model takes into account the tetrahedron as the basic structural unit and distinguishes the contribution of the hydrogen-bearing tetrahedra from the contribution of the hydrogen-free ones to the crystal phonon spectra.

Statistical strained-tetrahedron model of local ternary zinc blende crystal structures

The statistical strained-tetrahedron model was developed to overcome two common assumptions of previous models: 1) a rigid undistorted ion sublattice of regular tetrahedra throughout all five configurations, and 2) a random ion distribution. These simplifying assumptions restrict the range of applicability of the models to a narrow subset of ternary alloys for which the constituent binaries have equal or quasi-equal values of their lattice constants and standard molar enthalpies of formation (ΔfH0). Beyond these limits the predictions of such models become unreliable, in particular, when the ternary exhibits site occupation preferences. The strained-tetrahedron model, free from rigidity and stochastic limitations, was developed to better describe and understand the local structure of ternary zinc blende crystals, and interpret experimental EXAFS and far-IR spectra. It considers five tetrahedron configurations with the shape and size distortions characteristic of ternary zinc blende alloys, allows nonrando...

Raman Scattering and Far Infrared Reflection–Absorption Spectra of the Four‐Component Solid Solution ZnxCdyHg1−x—yTe

The Raman spectra for three compositions of Zn x Cd y Hg 1-x-y Te (ZMCT) solid solution were obtained at 300 K. The experimental method allowed us to observe TO-phonon lines. The comparison of the spectra for compositions with x = 0.02, y = 0.7 and x = 0.12, y = 0.17 shows the appearance of additional lines at 163 and 175 cm -1 besides two lines which are observed in the range 120 to 150 cm -1 . Far Infrared Reflection Spectra (FIRS) were obtained for five compositions. Theoretical models for three modes of the four-component solid solution were constructed for the interpretation of the FIRS spectra of ZMCT. We obtained good agreement between the results of RS and FIRS which allowed us to determine the LO- and TO-phonon frequencies for HgTe-, CdTe- and ZnTe-like lattices.

Statistical model analysis of local structure of quaternary sphalerite crystals

At the 2004 Ural International Winter School, we introduced the statistical strained tetrahedron model and discussed ternary tetrahedron structured crystals. The model allows one to interpret x-ray absorption fine structure (EXAFS) data and extract quantitative information on ion site occupation preferences and on the size and shape of each elemental constituent of the configuration tetrahedra. Here we extend the model to cover quaternary sphalerite crystal structures. We discuss the two topologically different quaternary sphalerite systems: the pseudo-balanced A1−xBxYyZ1−y (2:2 cation:anion ratio), and the unbalanced AxBx′C1−x−x′Z or AXyYy′Z1−y−y′ (3:1 or 1:3 cation:anion ratios) truly quaternary alloy systems. These structural differences cause preference values to vary with the relative contents in pseudo-quaternaries but to remain constant in truly quaternary compounds. We give equations to determine preference coefficient values from EXAFS or phonon spectra and to extract nearest-neighbor inter-ion d...

Magnetotransport phenomena in multimode lattices

The phonon and electron subsystems in the quaternary solid solutions of (ZMCT) were studied by means of Raman scattering and magnetophonon resonance. The Raman spectra for several compositions confirm that the phonon spectra exhibit three-mode behaviour. The cluster mode has also been observed. Four kinds of LO phonon (with HgTe-like, CdTe-like and ZnTe-like sublattices and ZnTe clusters) participate in the electron-phonon interaction. Four types of one-phonon magnetophonon resonance and two types of magnetophonon resonance on the difference of phonon frequencies have been observed. The peculiarities of the electron transport in these lattices are discussed.

CdxHg1-xTe phonon-spectra research by means of magnetophonon resonance

Abstract Magnetophonon oscillations of the transverse magnetoresistance of Cd 0.196 Hg 0.804 Te due to two-phonon transitions have been investigated in magnetic fields from 1.4 to 6T. An abundance of peaks has been traced, only the part of which had been interpreted in Sheregii et al . ( Pisma v JETF 47 , 613 (1988)) with using long-wave phonons. For the interpretation of all obtained peaks the short-wave phonons of both sublattices of HgTe-type and CdTe-type have been used. The frequencies of the extreme compounds HgTe (Kepa et al., Phys. Scripta 25 , 807 (1982)) and CdTe (Rowe et al., Phys. Rev. B10 , 671 (1974)) have been accepted as initials. The shift for the given composition of solid alloy has been calculated pos the best concord of the experimental peaks with calculated positions in the magnetic field of the corresponding resonances.

The stochastic model for ternary and quaternary alloys: Application of the Bernoulli relation to the phonon spectra of mixed crystals

To understand and interpret the experimental data on the phonon spectra of the solid solutions, it is necessary to describe mathematically the non-regular distribution of atoms in their lattices. It appears that such description is possible in case of the strongly stochastically homogenous distribution which requires a great number of atoms and very carefully mixed alloys. These conditions are generally fulfilled in case of high quality homogenous semiconductor solid solutions of the III–V and II–VI semiconductor compounds. In this case, we can use the Bernoulli relation describing probability of the occurrence of one n equivalent event which can be applied, to the probability of finding one from n configurations in the solid solution lattice. The results described in this paper for ternary HgCdTe and GaAsP as well as quaternary ZnCdHgTe can provide an affirmative answer to the question: whether stochastic geometry, e.g., the Bernoulli relation, is enough to describe the observed phonon spectra.

Magnetospectroscopy of symmetric and anti-symmetric states in double quantum wells

Abstract The experimental results obtained for magnetotransport in the InGaAs/InAlAs double quantum well (DQW) structures of two different shapes of wells are reported. A beating effect occurring in the Shubnikov–de Haas (SdH) oscillations was observed for both types of structures at low temperatures in the parallel transport when the magnetic field was perpendicular to the layers. An approach for the calculation of the Landau level energies for DQW structures was developed and then applied to the analysis and interpretation of the experimental data related to the beating effect. We also argue that in order to account for the observed magnetotransport phenomena (SdH and integer quantum Hall effect), one should introduce two different quasi-Fermi levels characterizing two electron subsystems regarding the symmetry properties of their states, symmetric and anti-symmetric ones, which are not mixed by electron–electron interaction.

Parallel magnetotransport in multiple quantum well structures

The results of investigations of parallel magnetotransport in AlGaAs/GaAs and InGaAs/InAlAs/InP multiple quantum-well structures (MQWs) are presented. The MQWs were obtained by metalorganic vapor phase epitaxy with different shapes of the QWs, numbers of QWs, and levels of doping. The magnetotransport measurements were performed in a wide region of temperatures (0.5–300 K) and at high magnetic fields up to 30 T (B is perpendicular to and the current is parallel to the plane of the QW). Three types of observed effects are analyzed: the quantum Hall effect and Shubnikov—de Haas oscillations at low temperatures (0.5–6 K) and magnetophonon resonance at higher temperatures (77–300 K).