Theory of magnetic susceptibility of the narrow-gap semiconductors Pb(Sn)Te

The nonoscillating singular part of the susceptibility of Pb_1?xSn_xTe alloys is calculated. The dependence on the composition x, temperature and the carrier concetration is explained by the existence of the valence band, separated from the conduction band with a small energy gap.     

Low-temperature electrical conductivity and the superconductor-insulator transition induced by indium impurity states in (Pb0.5Sn0.5)1 ? xInxTe solid solutions

A study is reported of the low-temperature electrophysical (including superconducting) characteristics of the (Pb_0.5Sn_0.5)_{1 − x} In _x Te semiconducting solid solutions with an indium content variable within x = 0.05–0.20. A decrease in the impurity content x in the material has been found to bring about a decrease in the superconducting transition temperature T _c and the onset of an “insulating” state of the material. These effects manifest themselves in an increase in the low-temperature (T = 4.2 K) resistivity of (Pb_0.5Sn_0.5)_0.95In_0.05Te by more than three orders of magnitude as compared to that of (Pb_0.5Sn_0.5)_0.8In_0.2Te. A decrease in the In content in the solid solution also gives rise to a radical change in the shape of the temperature dependence of the electrical resistivity from a metallic behavior in the material with x = 0.20 (decrease in the electrical resistivity with decreasing temperature in the range 300–4.2 K) to a semiconducting behavior in a sample with x = 0.05 (exponential increase in the resistivity at T < 25 K). This transition to the insulating state with decreasing content of the impurity should be assigned to the displacement of the impurity band of quasi-local indium states toward the top of the light-hole valence band of the material and its emergence into the band gap of the solid solution.     

Superconducting properties of PbxSn1−xTe

Superconducting transition temperatures and critical magnetic field curves on low carrier concentration Pb_xSn_1?xTe samples where 0.25 ?x?0.55 are reported. These data are interpreted in terms of a changing band structure from that of SnTe to one which is similar to that of GeTe. The importance of carriers (holes) in secondary maxima of the valence band is emphasized.     

Enhancement of the power factor of Pb1–xSnxTe (0.00 ≥ x ≥ 0.08) alloys

Thermoelectric properties of Pb_1–x Sn _x Te (0.00 ≥ x ≥ 0.08) alloys synthesized by melting-quenching-annealing method have been investigated. The sample structure and phases have been investigated by Raman spectroscopy and X-ray diffraction, while the morphology and stoichiometry have been studied by SEM and EDX. The nanomaterial exists in a single phase and has a face-centred cubic (fcc) lattice of rock-salt type in the whole range of x values in Pb_1–x Sn _x Te alloys. The effect of tin substitution on the lattice vibration and chemical bonding nature in the lead telluride has been investigated by Raman spectroscopy at room temperature. The Seebeck coefficient and electrical resistivity have been measured in the temperature range of 100–400 K. The electrical resistivity measurements reveal that the compounds have extrinsic to intrinsic conduction transition and the electrical temperature transition shifts to higher values with increasing the Sn content. For all studied compounds, the Seebeck coefficient is positive indicating predomination of positive charge carriers over the entire temperature range. The thermoelectric power factor was enhanced to 2.03 mWm^?1 K^?2 for the sample with 4% Sn content at room temperature.     

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.     

Dynamical nonlinear refraction in PbTe/Pb1−xSnxTe MQWs

An analysis of nonlinear refraction due to the dynamical free carrier filling of minibands in PbTe/Pb_1−xSn_xTe (X = 0.2) MQEs on (111) BaF₂ substrates is presented. The results are compared with those for bulk Pb_1−xSn_xTe layers. The abrupt substantial increase of n(I) in MQWs is connected with crossing of the minibands in oblique valleys of Pb_1−xSn_xTe wells by the Fermi quasi-level.     

On the type of superlattices in leadtintelluride system

It is predicted in the PbTePb_1?xSn_xTe superlattice (SL) that the bottom of the quantum well is situated at the PbTe layer in n-type specimens and the top at the Pb_1?xSn_xTe layer in p-type ones for x<0.23, and for x>0.23, SLs are of type II. These predictions are based upon an experimental tin concentration dependence of the band edge energies relative to the Fermi level pinned by amphoteric indium impurities in bulk Pb_1?xSn_xTe. In n-type PbTePb_0.8Sn_0.2Te SL, cyclotron resonances together with Hall coefficient and Shubnikov de Haas (SdH) oscillation experiments support the existence of the PbTe wells. The results of submillimeter cyclotron resonances for n-type PbSe_0.08Te_0.92Pb_0.8Sn_0.2Te and PbSePb_0.88Sn_0.12Se SLs are also presented.     

The laser-irradiated transformation of intrinsic and impurity defects in narrow-gap Pb1 − xSnxTe

Changes in the electrical and optical properties of the narrow-gap solid solution Pb_{1 − x}Sn_xTe (0 ⩽x⩽ 0.20) after IR laser radiation treatment were investigated. The considerable reduction (by a factor of ~10²) of hole concentration and a gain in hole mobility was established. Transformation of the EPR spectra of Mn doped PbTe was also observed.The observed changes in the properties of Pb_{1 − x}Sn_xTe single crystals are connected with the transformation of the intrinsic and impurity defect states of Pb_{1 − x}Sn_xTe and with the drop in the microinclusions enriched with metal components of Pb_{1 − x}Sn_xTe or metal impurities. The resulting thermodiffusion of the metallic atoms to the electrically active vacancies of Pb(Sn) in the Pb_{1 − x}Sn_xTe lattice explains the reduction of hole concentration and gain in mobility.     

Irradiation-induced defect states in Pb1−xSnxTe under high pressure

Abstract

The galvanomagnetic properties of electron-irradiate n^? and P-Pb_1?x,Sn_xTe (x=O.2) under high hydrostatic Pressure have been investigated. In the irradiated samples the “soft” stabilisation of Fermi level under the irradiation has been revealed and the model of the energy spectrum of irradiated Pb_1?x,Sn_xTe (x=O.2) proposed. The obtained experimental results were used to aetermine the Parameters of radiation-induced resonant band situated slightly below the valence band top.     

On the Fermi surface of low carrier concentration SnTe

The multiple parallel frequency branches observed in low carrier concentration SnTe by Savage et al. in 1972 are interpreted in terms of the structural phase transition in such material in conjunction with band structure parameters derived from a study of the Shubnikov-de Haas effect in samples of Pb_1?xSn_xTe in the rhombohedral phase with normal and inverted band ordering.     

Model of magnetic anisotropy in disordered semimagnetic semiconductors

We propose a model explaining the origin of cubic magnetic anisotropy in disordered semiconductor. We show that the magnetic anisotropy changes with the position of the Fermi energy in the valence band and the level of disorder in the crystal. The method is applied to Pb_1−x−ySn_yMn_xTe and Sn_1−xMn_xTe ferromagnetic semiconductor crystals.     

Spin resonant optical four wave mixing in Pb1−xSnxTTe epitaxial layers and in Pb1−xSnx/PbTe superlattices

Spin resonances of the third-order non-linear susceptibility of epitaxial layers of n- and p-type Pb_1?xSn_xTe and Pb_1?xSn_xTe/PbTe superlatttices have been observed by four photon mixing of the radiation of two CO₂-lasers. Precise data on the effective g-values of the electrons and holes of Pb_1?xSn_xTe were obtained. These data and the results of magneto-optical interband absorption measurements are used to obtain k·p parameters within the Mitchell and Wallis band model. In the Pb_1?xSn_xTe/PbTe superlattices, the same g-values for electrons as in the Pb_1?xSn_xTe films with the same composition x are found. Consequently, the electrons in the superlattices are confined within the Pb_1?xSn_xTe layers. Therefore the Pb_1?xSn_xTe/PbTe system forms a type I and not a staggered superlattice.     

Quantum oscillation of carrier concentration due to fermi level pinning by doped indium impurities in Pb1−XSnXTe

The Shubnikov-de Haas like oscillation and rapid increase of the carrier concentration above the quantum limit magnetic field (H₀) are observed in Pb_1?xSn_xTe doped with indium (x=0.33 and 0.35). Experimental results can be reproduced satisfactorily by the calculation based on the Fermi level pinning model due to In-impurities, where we take into account the level broadening (Г) effect of the band structure. It is confirmed that the increasing rate of carrier concentration with respect to magnetic field above H₀ decreases with larger Г.     

p型Ag0.5(Pb8－xSnx)In0.5Te10化合物的制备及其热电性能

采用高温熔融缓冷和放电等离子烧结工艺制备了p型Ag_0.5(Pb_8-xSn_x)In_0.5Te₁₀五元化合物.研究了Sn含量对化合物载流子传输特性及热电性能的影响规律.结果表明：在Ag_0.5(Pb_8-xSn_x)In_0.5Te₁₀(x 关键词： 0.5(Pb_8-xSn_x)In_0.5Te₁₀')" href="#">Ag_0.5(Pb_8-xSn_x)In_0.5Te₁₀ 合成 载流子 热电性能     

High pressure phase transition in PbSnTe

The high pressure structural phase transition in the alloy series Pb_{1 ? x}Sn_xTe has been investigated using resistivity and Hall coefficient measurements. With increasing of tin content the critical pressure decreases linearly and the phase transition becomes less drastic. The anomalous behavior of the resistivity in the phase transition region is explained by band structure changes. It is suggested that the high pressure phase transition in Pb_{1 ? x}Sn_xTe is a metallic-covalent transition.     

Light-induced intrinsic defects in PLZT ceramics

This paper reports on an EPR study of a ferroelectric, 1.8/65/35, and an antiferroelectric, 2/95/5, of optically transparent Pb_1?y La_yZr_1?x Ti_xO₃ (PLZT) ceramics within a broad temperature range (20–300 K) after illumination at a wavelength of 365–725 nm. Illumination with ultraviolet light, whose photon energy corresponds to the band gap of these materials, at T<50 K creates a number of photoinduced centers: Ti³⁺, Pb⁺, and Pb³⁺. It is shown that these centers are generated near a lanthanum impurity, which substitutes for both the Pb²⁺ and, partially, Ti⁴⁺ ions through carrier trapping from the conduction or valence band into lattice sites. The temperature ranges of the stability of these centers are measured, and the position of their local energy levels in the band gap is determined. The most shallow center is Ti³⁺, with its energy level lying 47 meV below the conduction band bottom. The Pb³⁺ and Pb⁺ centers produce deeper local levels and remain stable in the 2/95/5 PLZT ceramics up to room temperature. The migration of localized carriers is studied for both ceramic compositions. It is demonstrated that, under exposure to increased temperature or red light, the electrons ionized into the conduction band from Ti³⁺ are retrapped by the deeper Pb⁺ centers, thus hampering the carrier drift in the band and the onset of photoconduction. The part played by localized charges in the electrooptic phenomena occurring in the PLZT ceramics is discussed.     

Determination of the susceptibility mass of heavy holes in Pb1−xSnxTe compounds by plasma reflection spectra

Plasma reflection spectra of the Pb_1?xSn_xTe alloy samples with x = 0.19 have been studied in the temperature range 82–400 K. It has been found out that the plasma minimum is shifted towards long waves with an increase of temperature from 82 to 300 K. This shift is caused by the increase of the hole mass because of hole redistribution into an additional band. A susceptibility mass of the additional band of heavy holes has been determined. Its value turned out equal to 0.144m₀.     

Electrical properties of Pb1−xSnxSe semiconducting alloys

The influence of valence-conduction band inversion upon the electrical properties of degenerate Pb_1−xSn_xSe has been studied experimentally as a function of temperature, free carrier concentration, and alloy fraction x. It is found that breaks occur in the temperature dependence of the resistivity at the temperature T₀ of band-inversion. These break temperatures T_B are shown to be independent of carrier concentration, a result which supports the band-inversion model.     

Recent advances in lead-chalcogenide diode lasers

The fundamental material properties of Pb_1−xSn_xTe, PbS_1−xSe_x and Pb_1−xSn_xSe are reviewed. Expressions for the temperature and compositional dependences of the band parameters and dielectric constants based on recently published data are presented. As far as device technology is concerned, crystal growth techniques and diode fabrication procedures which are in use today are reviewed and compared. A comprehensive summary of laser properties like threshold current density, output power, efficiency, maximum operating temperature and tuning range of different diode structures are presented. Application related aspects such as long term stability are treated. Recent progress in laser theory is applied to explain experimentali _th vs.T curves. The various laser applications are reviewed briefly. A new technique for monitoring gas concentrations using pulsed lasers and an integral method for signal processing is discussed and compared with the differential absorption, derivative spectroscopy. A long-path trace-gas monitoring system incorporating this new technique is presented.     

Theoretical analysis of the electronic,optical and thermal properties of lead strontium telluride alloys Pb1−xSrxTe (x = 0.0−1.0)

We have simulated different physical properties of Pb_1?xSr_xTe semiconductors, using the Ab-initio full potential augmented plane wave (FP-LAPW) method. The two commonly used exchange potentials viz., PBE-GGA and WC-GGA are used along with the most recently developed modified Becke and Johnson (mBJ) potential to study the electronic and optical properties. In this study, we have observed an increase in band gap values as well as the lattice parameter with increasing the concentration of Sr atoms in Pb_1?xSr_xTe alloys while the bulk modulus and the refractive index have reverse effect. The microscopic origin of the band gap bowing is explained using the approach of Zunger and co-workers. At ambient conditions (p = 0, T = 0), the calculations indicate that Pb_1?xSr_xTe is a direct band gap semiconductor R–R with x = 0.125, 0.25, 0.375, 0.5, 0.625, 0.75 and 0.875. The refractive indices are also calculated using the FP-LAPW method and the models of Moss, Ravindra and the Herve–Vandame. The obtained results are in consistent with the previous available data. To study the thermal effects, the temperature effect on the lattice parameters, thermal expansions, heat capacities the quasi-harmonic Debye model is applied. The Debye temperature is determined from the non-equilibrium Gibbs function.