E. P. Skipetrov

Electric and magnetic characterization of impurity-induced states in diluted magnetic Pb1-yYbyTe semiconductors

In the present paper we report on results obtained by complex investigations of galvanomagnetic and magnetic properties of a diluted magnetic semiconductor Pb 1-y Yb y Te. Ytterbium doping modifies the energy spectrum of charge carriers in lead telluride by formation of deep impurity levels, moving from valence to forbidden band with increase of ytterbium content. The paramagnetic Curie-Weiss response observed has revealed a small fraction of Yb ions in magnetically active Yb 3 charge state, while the majority of impurity ions are in non-magnetic Yb 2+ state. We couple the magnetic and galvanomagnetic data in a model of charge carriers energy spectrum in Pb 1-y Yb y Te, for which energy position and electron population of the ytterbium level are derived as a function of impurity concentration.

Electronic structure of lead telluride-based alloys, doped with vanadium

The crystal structure, composition, galvanomagnetic properties in low magnetic fields (4.2u2009Ku2009≤u2009Tu2009≤u2009300u2009K, Bu2009≤u20090.07u2009T), and the Shubnikov–de Haas effect (Tu2009=u20094.2u2009K, Bu2009≤u20097u2009T) are studied in Pb1−x−ySnxVyTe (xu2009=u20090, 0.05–0.18) alloys synthesized by the Bridgman technique with variable vanadium impurity concentrations. It is shown that increasing the vanadium content leads to the formation of regions enriched in vanadium and of microscopic inclusions of compounds with compositions close to V3Te4. In Pb1−yVyTe stabilization of the Fermi level by a deep vanadium level, an insulator–metal transition, and a rise in the free electron concentration are observed as the vanadium content is increased. The variation in the free charge carrier concentration with increasing vanadium concentration in Pb1−yVyTe and Pb1−x−ySnxVyTe (xu2009=u20090.05–0.18) alloys is compared. Possible models for rearrangement of the electronic structure in Pb1−x−ySnxVyTe alloys with vanadium doping are discussed.

On Fermi level pinning in lead telluride based alloys doped with mixed valence impurities

Abstract The galvanomagnetic (4.2≤T≤300 K, B≤0.1 T) properties of n-Pb1−yMnyTe (0.07≤y≤0.11) and n-Pb1−xGexTe (0.04≤x≤0.08) doped with In and Ga (CIn≈0.5 mol%, CGa≈1.5–2 mol%, respectively) before and after the irradiation with fast electron (E=6 MeV, Φ≤1.85×1017 cm−2) have been investigated. Impurity-induced deep levels EIn and EGa were observed in the alloys studied. Their energy position was determined and the energy level diagrams as a function of alloy composition were constructed. It was found that the electron irradiation has nearly no effect on the properties of Pb1−yMnyTe〈In〉, while in Pb1−xGexTe〈Ga〉 it causes a transition to metal-type conductivity. It was concluded that the gallium-induced level EGa, unlike the level EIn does not stabilize the Fermi level in PbTe based alloys.

Electronic structure of chromium-doped lead telluride-based diluted magnetic semiconductors

The crystal structure, composition, galvanomagnetic, and oscillatory properties of Pb1−x−ySnxCryTe (x=0,0.05–0.30; y⩽0.01) alloys are studied for different matrices and chromium impurity concentrations. It is shown that impurity chromium ions dissolve in the lattice in amounts below 1mol.%, while higher chromium concentrations lead to the appearance of microscopic regions with elevated chromium contents and inclusions of chromium-tellurium compounds. Reductions in the hole concentration, p−n conversion of the conductivity type, and stabilization of the Fermi level by the resonance level of chromium are observed with increasing chromium content. The initial rates of change of the charge carrier concentrations during doping are determined. A two-band Kane dispersion relation is used to calculate the electron concentration and Fermi level as functions of the tin content. A diagram showing the rearrangement of the electronic structure of the chromium doped alloys with varying matrix composition is constructed.

Vanadium deep impurity level in diluted magnetic semiconductors Pb1 − x − ySnxVyTe

The crystal structure, Sn and V distribution over the length of single-crystal ingots, and galvanomagnetic effects in low magnetic fields (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) in Pb1−x−ySnxVyTe alloys (x = 0.05−0.21, y ≤ 0.015) are studied. It is shown that all the samples are single-phase, while the Sn and V concentrations exponentially increase from the beginning to the end of the ingots. Upon doping with V, a decrease in the concentration of free holes and a metal-insulator transition are found. They are related to the appearance of a deep impurity level of V in the band gap, electron redistribution between the level and the valence band, and pinning of the Fermi-level to the impurity level. The shift rate of the V level relative to the conduction band bottom is determined and a diagram of the reconstruction of the electronic structure of the Pb1 − x − ySnxVyTe alloy upon varying the host composition is suggested.

Galvanomagnetic properties and electronic structure of Pb1?x?ySnxVyTe under pressure

We study the galvanomagnetic properties in weak magnetic fields (4.2 ? T ? 300 K, B ? 0.07? T) and the Shubnikov-de Haas effect (T = 4.2 K, B ? 7 T) in single crystal Pb1?x?ySnxVyTe alloys under variation of alloy composition (x = 0.05?0.20, y ? 0.01) and hydrostatic compression up to 15 kbar. The increase of vanadium impurity content leads to the p-n-conversion and to a transition in the insulating phase due to the pinning of Fermi level by the donor-type deep vanadium impurity level situated under the bottom of the conduction band. We found that pressure induces a decrease of the activation energy of the vanadium level, the n-p-inversion of the conductivity type at low temperatures and an insulator?metal transition. In the metallic phase, a sharp increase of the Hall mobility (up to 3???105?cm2? V?1? s?1) and appearance of Shubnikov-de Haas oscillations are observed at helium temperature. The pressure and temperature coefficients of vanadium deep level energy are determined, and the diagram of the electronic structure rearrangement for Pb1?x?ySnxVyTe under pressure is proposed.

Ferromagnetism in diluted Pb1 − x − yGexCryTe magnetic semiconductors

Magnetic properties of Pb1 − x − yGexCry Te alloys (x = 0.02–0.20, y = 0.01–0.08) were studied. It was detected that the magnetic susceptibility of alloys consists of two contributions: the paramagnetic Curie-Weiss part (the temperature region is T < 50 K) caused, probably, by the Cr3+ ion paramagnetism, and the high-temperature ferromagnetic part (T < 300 K). The dependences of the concentration of magnetic centers on the composition of the matrix were obtained from the paramagnetic and ferromagnetic contributions. It was shown that a decrease in the concentration of paramagnetic centers can be, at least qualitatively, explained by the transformation of the electronic structure as the germanium concentration increases. A phenomenological model was suggested, which explains the behavior of magnetic properties as the chromium content increases, and possible mechanisms of ferromagnetic ordering in studied alloys are discussed.

The kinetics of the changes in charge carrier concentration with doping, for lead telluride-based alloys with transition metal impurities

A study of the crystal structure, phase and elemental composition, and galvanomagnetic properties of transition metal (Sc, Ti, Cr, V and Fe) doped alloys, based on lead telluride and synthesized using the Bridgman method. We determined the distribution of solid solution components along the length of single-crystal ingots. It is found that the increase in the impurity leads to the appearance of regions enriched with impurity content and microscopic inclusions of compounds similar in structure to the known compounds of impurity atoms with tellurium. We found a p-n inversion of conductivity type, metal-dielectric and dielectric-metal transitions, and pinning of the Fermi level by deep impurity levels, with increasing impurity content. We compare the kinetics of changes in the concentration of free charge carriers and the Fermi energy with doping, varying matrix composition, and type of impurity. A general model for reorganizing the electron structure of the studied alloys with doping, is proposed.

On the resonant level of chromium in the rhombohedral and cubic phases of Pb1 − x − yGexCryTe alloys

The temperature dependences of the Hall coefficient (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) in Pb1 − x − yGexCryTe alloys (x = 0.03–0.08, y ≤ 0.01) are studied. An increase in the absolute value of the Hall coefficient with an increase in temperature is found. This fact is indicative of a decrease in the concentration of free electrons as a result of the motion of the resonant level of chromium stabilizing the Fermi level relative to the conduction-band bottom. The temperature dependences of the Hall coefficient, in satisfactory agreement with the experimental ones, are calculated in the context of the two-band Kane dispersion law allowing for the structural phase transition upon increasing temperature. The energy position and temperature coefficients of the motion of the resonant level of chromium relative to the middle of the band gap in the rhombohedral and cubic phases are determined.

Magnetic properties of diluted magnetic semiconductors Pb1–yFeyTe

The phase and elemental composition and magnetic properties (Bu2009≤u20097.5 T, 2.0u2009Ku2009≤u2009Tu2009≤u200970u2009K) of Pb1–yFeyTe alloys were studied under varied impurity concentration along the Bridgman-grown single-crystal ingot. The distribution of iron impurity along the length of the ingot in the main phase and the composition of microscopic inclusions of the second phase were determined. It was established that the magnetization of the samples contains several contributions: the paramagnetic contribution of impurity ions, crystal lattice diamagnetism, as well as the contributions of free charge carriers, charge carriers in the impurity band, clusters of iron ions, and the oscillating contribution of the de Haas–van Alphen effect. These contributions were systematically separated. Using an approximation for the magnetic field and temperature dependences of the impurity-ion contribution by a sum of two terms based on the modified Brillouin functions, we determined the variation of the concentration of iron ions in two differe...