The voigt-type microwave Kerr effect in semiconductors with spherical constant energy surfaces1

A plane wave analysis is given for the free-carrier, microwave magneto-Kerr effect in semiconductors having spherical constant energy surfaces for the case of the applied static magnetic field perpendicular to the propagation direction (Voigt-type Kerr effect). The analysis is in terms of R_v, the complex polarization factor of the reflected wave. The behavior of R_v is considered in detail for low magnetic fields. Multiple-carrier conduction and energy-dependent scattering are shown to give rise to major contributions to R_v. Computer curves for |R_v|vs. μ_eB, $\text{n}\text{p}$ and ω are presented for parameters corresponding to InSb. Approximate expressions for R_v, which are valid for low magnetic field, high-loss conditions, are given and compared with curves computed from the more complex expressions. Room temperature data for R_v are presented for TE₁₁ waves in a circular waveguide. The dependence of R_v on magnetic flux density is shown for intrinsic InSb. The data are compared with the plane wave predictions. Experimental data for the magneto-Kerr effect are also given for magnetic fields slightly misaligned from the Voigt orientation. An empirical model is introduced which describes these data in terms of data for the Faraday and Voigt orientations of the magnetic field. This model is shown to be of value for alignment of the magnetic field in the Voigt orientation, and for measurement of the Voigt-type Kerr effect in the presence of any small, remaining longitudinal magnetic field component.     

Acceptor states in cubic semiconductors having a large hole-mass ratio

In cubic semiconductors the hole-mass ratio is small, which makes it possible to use the zero light-hole-mass limit. It was found that variational methods in this popular limit are not necessary to solve the Luttinger equation and not only the entire energy spectrum for the bound states of an acceptor and the eigenfunctions, including in momentum space, but also the behavior of the eigenfunctions at large radii can be determined to a high degree of accuracy. This approach made it possible to suggest comparatively simple relations for the lowest states of each series having different angular momenta, covering the entire range of possible mass ratios for semiconductors. Fiz. Tverd. Tela (St. Petersburg) 41, 1556–1563 (September 1999)     

Polar optical phonon scattering limited free carrier absorption in semiconductors with ellipsoidal energy band structure

A formula is derived for the calculation of free carrier absorption in semiconductors with ellipsoidal energy band structure, including the effects of electron screening, when the dominant scattering mechanism is due to polar modes. Computational results are also presented which show that the magnitude of the FCA is significantly affected by the mass anisotropy coefficient.     

High-field magnetoresistance and magnetothermal e.m.f. in many-valley semiconductors with ellipsoidal energy surface

Thermomagnetic coefficients appropriate to a many-valley model of a semiconductor of the n -Germanium type are evaluated in the framework of the density matrix formalism developed earlier. These coefficients are determined for arbitrary values of the magnetic field, within the effective mass approximation. The phonon-drag contribution is not included in this work. An application is made to the four-ellipsoidal model of n-Ge under the conditions where elastic-acoustic phonon scattering is the predominant mechanism of scattering and the high-temperature limit of the phonon distribution is valid. The thermoelectric power (magneto-Seebeck effect) is found to increase with increasing values of the magnetic field except for a small region of low magnetic field values where it decreases in the longitudinal configuration only.     

Free carrier Voigt magneto-absorption in cubic semiconductors

A compensation bridge for measuring Voigt magneto-absorption in semiconductors has been setup for X-band. Room temperature measurements for phase and amplitude, as a function of magnetic field up to 9.8 kOe, have been carried on n-type single crystals of germanium, at 9.02 GHz. Theoretical calculations have been done for the amplitude and phase measurements as a function of magnetic field taking into account lattice scattering. There is a good agreement between the experimental and the theoretical results.     

Excitons in direct band gap cubic semiconductors

Perturbation is applied to study of the Wannier-Mott excitons in direct band gap cubic semiconductors with a fourfold degenerate highest valence band. The fine structure of exciton energy levels is investigated. General formulae are derived for the matrix elements of the perturbation. From these expressions it is straightforward to obtain values of the fine structure splittings of the energy levels and the wave functions of corresponding staes in any order of perturbation theory. A comparison with results of previous works is made.     

Higher excited states of acceptors in cubic semiconductors

For the first time, higher excited states of shallow acceptors up to the 3s and 4s states are calculated based on the Balderschi and Lipari theory including the cubic correction. The eigenvalues and eigenvectors of the effective mass Hamiltonian for shallow acceptor states were obtained by the finite element method. The resultant sparse matrix is diagonalized by a newly developed Saad's method based on Arnoldi's algorithm. Comparison with experimental spectra on ZnTe:Li and ZnTe:P gives best valence band parameters for ZnTe; μ = 0.60 and δ = 0.12.     

Band energy structure calculations and spin effect in zinc-blende semiconductors

Band energy structure of the n-doped zinc-blende semiconductor was calculated using norm-conserving pseudopotential and Green function methods. The calculations for the semiconductor with different dopant contents were performed in the presence of external circularly polarized axial and polar dc-field potentials. Changes in the spin density distribution for the clusters with different dopant concentrations and at different lattice temperatures and an enhancement of the spin-polarized delocalization states in the presence of the dc-field potential were observed. The observed photo-induced spin effects were explained within a framework of the band energy model of spin physics of taking into account of the photo-induced electron–phonon anharmonicity. The results are consistent with those obtained in experiments of photospintronics.     

Influence of magnetic quantization on the debye screening length in degenerate semiconductors having parabolic energy bands

The Debye screening length in degenerate semiconductors having parabolic energy bands is shown for the first time to have an oscillatory dependence on magnetic field under the influence of Landau quantization when the higher lying sub-bands are occupied.The authors are indebted to Professor J. N.Bhar for his keen interest in the work.     

Prediction of lattice constant in cubic perovskites

Regularities of lattice constant in ideal perovskites are investigated by using a total of 132 ABX₃-type compounds, including oxides and halides. Two atomic properties; the sum of ionic radius of B and X atoms and the well known ‘tolerance factor’ (which is a function of ionic radius of A, B and X), were found very effective in reproducing the measured lattice constant through a linear combination of these two parameters (R²=0.995). It is further indicated that these two parameters are linked to the crystal features of perovskite. The average error limits in predicting lattice constant, by using this empirical equation, are expected within 0.63%. It may be useful to design new substrates/buffer materials for compound semiconductor epitaxy, in which there is a requirement of lattice match between them and adjacent layers.     

The hall effect in liquid semiconductors

The proper interpretation of the Hall coefficient R_H of liquid semiconductors is still an unsolved problem, and it is a particularly interesting one in view of the frequently observed discrepancy in sign with the Seebeck coefficient. We present some new data which include measurements of the Hall mobility μ_H in liquid thallium-tellurium through the composition range where the Seebeck coefficient S changes sign, and in the range where S is negative. An abrupt change in magnitude of μ_H occurs at the intrinsic composition (Tl₂Te, where S changes sign), and μ_H is observed to have an appreciable dependence on temperature only at this composition. This is consistent with transport by carriers in two bands. μ_H is lower on the Tl-rich side of Tl₂Te, and the formula n_H = 1/R_He yields a value for n_H which is ten times larger than the electron concentration inferred from the composition, assuming that electrons are derived from the Tl in excess of Tl₂Te. We review the various suggested interpretations of the Hall effect in liquid semiconductors from several points of view, and conclude that the conventional formula n = ± 1/R_He is unreliable for inferring either the sign or concentration of the carriers.     

Intrinsically minimal thermal conductivity in cubic I-V-VI2 semiconductors

We report measurements of the thermal conductivity of high-quality crystals of the cubic I-V-VI2 semiconductors AgSbTe2 and AgBiSe2. The thermal conductivity is temperature independent from 80 to 300 K at a value of approximately 0.70 W/mK. Heat conduction is dominated by the lattice term, which we show is limited by umklapp and normal phonon-phonon scattering processes to a value that corresponds to the minimum possible, where the phonon mean free path equals the interatomic distance. Minimum thermal conductivity in cubic I-V-VI2 semiconductors is due to an extreme anharmonicity of the lattice vibrational spectrum that gives rise to a high Grüneisen parameter and strong phonon-phonon interactions. Members of this family of compounds are therefore most promising for thermoelectric applications, particularly as p-type materials.