L. A. Skipetrova

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.

Gallium-induced defect states in Pb1-xGexTe alloys

Galvanomagnetic effects (B ≤ 0.1 T, 4.2 ≤ T < 300 K) in n-Pb 1-x Ge x Te( (0.04 ≤ x ≤ 0.08) alloys doped with gallium (1.5-3 at%) have been investigated as well as before and after the irradiation with fast electrons (T 300 K, E = 6 MeV, Φ ≤ 2.4 × 10 16 cm -2 ). Low-temperature activation range on temperature dependencies of the resistivity and the Hall constant has been revealed in the alloys with low initial gallium concentration. Increasing in the gallium content as well as fast-electron irradiation lead to the transition to the metal-type conductivity in the samples. The results were explained under assumption that gallium doping induced the appearance of deep impurity level in the gap of the alloys. The position of the gallium level in depending on the alloy composition was determined.

Fermi level pinning in Fe-doped PbTe under pressure

We synthesize an iron-doped PbTe single-crystal ingot and investigate the phase and the elemental composition as well as galvanomagnetic properties in weak magnetic fields (4.2 K≤T≤300 K, B ≤ 0.07 T) of Pb1−yFeyTe alloys upon varying the iron content, at atmospheric pressure and under hydrostatic compression up to 10 kilobars. We find an increase of iron concentration along the length of the ingot and the appearance of microscopic inclusions enriched with iron in the heavily doped samples. Lightly doped alloys are characterized by the p-type metal conductivity. An increase of the iron impurity content leads to a decrease in the free hole concentration, a stabilization of galvanomagnetic parameters, indicating the pinning of the Fermi energy by the iron resonant impurity level lying under the bottom of the valence band, and to the p-n inversion of the conductivity type. Under pressure, the free hole concentration in the sample, in which the stabilization of galvanomagnetic parameters takes place, increases...

Scandium resonant impurity level in PbTe

We synthesize a scandium-doped PbTe single-crystal ingot and investigate the phase and the elemental composition as well as galvanomagnetic properties of Pb1-yScyTe alloys in weak magnetic fields (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) upon varying the scandium content (y ≤ 0.02). We find that all investigated samples are single-phase and n-type. The distribution of scandium impurities along the axis of the ingot is estimated to be exponential. An increase of scandium impurity content leads to a monotonous growth of the free electron concentration by four orders of magnitude (approximately from 1016 cm−3 to 1020 cm−3). In heavily doped alloys (y > 0.01), the free electron concentration at the liquid-helium temperature tends to saturation, indicating the pinning of the Fermi energy by the scandium resonant impurity level located on the background of the conduction band. Using the two-band Kane and six-band Dimmock dispersion relations for IV-VI semiconductors, dependences of the Fermi energy measured from the bott...

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.

Galvanomagnetic properties and electronic structure of iron-doped PbTe

We synthesize an iron-doped PbTe single-crystal ingot and investigate the phase composition and distribution of the iron impurity along the ingot as well as galvanomagnetic properties in weak magnetic fields (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) of Pb1−yFeyTe alloys. We find microscopic inclusions enriched with iron and regions with a chemical composition close to FeTe in the heavily doped samples, while the iron impurity content in the main phase rises only slightly along the length of the ingot reaching the impurity solubility limit at approximately 0.6 mol. %. Samples from the initial and the middle parts of the ingot are characterized by p-type metal conductivity. An increase of the iron impurity content leads to a decrease in the free hole concentration and to a stabilization of galvanomagnetic parameters due to the pinning of the Fermi level by the iron resonant impurity level EFe lying under the bottom of the valence band (Ev − EFe ≈ 16 meV). In the samples from the end of the ingot, a p-n inversion of t...

Ferromagnetism in Diluted Magnetic Semiconductors Pb1-x-yGexCryTe

Magnetic and galvanomagnetic properties of Pb1-x-yGexCryTe (x=0.02-0.20, y=0.01-0.08) solid solutions have been investigated. It was found that the magnetic susceptibility of these alloys contains two contributions: a paramagnetic Curie-Weiss share (T<50 K) due to the paramagnetism of Cr3+ ions and a high temperature ferromagnetic share (T<300 K). Dependence of the concentration of paramagnetic centers on the composition of the matrix was obtained. The magnetic field dependences of the Hall coefficient in the vicinity of the metal-insulator transition were measured and the main parameters of charge carriers in terms of the two-band conduction model were estimated. The experimental results are discussed in the framework of the electronic structure model, assuming varying electrical and magnetic activities of Cr ions as function of germanium content in the alloys.

Galvanomagnetic and Magnetic Properties of Pb1-yScyTe

The galvanomagnetic properties in weak magnetic fields (4.2≤T≤300 K, B≤0.07 T) as well as magnetic properties (2≤T≤300 K, B≤9 T) of the single-crystal Pb1-yScyTe (y≤0.02) alloys have been investigated. We find that an increase of Sc impurity content leads to a monotonous growth of the free electron concentration (from 1016 cm-3 to 1020 cm-3). In heavily doped alloys (y>0.01), it tends to saturation, indicating the pinning of the Fermi energy by the scandium resonant level located inside the conduction band. The energy of the level is estimated (ESc≈Ec+280 meV) and the model of electronic structure rearrangement of Pb1-yScyTe alloys with doping is proposed. In the frame of this model, using experimental temperature and magnetic field dependences of magnetization, the concentrations of magnetically active scandium ions are determined and connection of the electronic structure with the magnetic properties of the alloys are discussed.

Impurity-induced photoconductivity in gallium-doped Pb1−xGexTe alloys

Photoelectric properties of Pb1� xGexTehGai (0:044x40:08) alloys were investigated under controlled infrared illumination. At least two types of relaxation processes of the photoconductivity after removing the illumination at T5Tc � 60 K and an anomalous peak of negative photoconductivity followed by characteristic delay time on the front of kinetic curves were observed. Results were explained assuming the photoexcitation of the electrons from galliuminduced defect states to the conduction band and existing energy barrier separating localized and band states in configuration space. Appearance of a negative photoconductivity peak was attributed to the phase transition of the alloys from the rhombohedral phase to the cubic one due to the reconstruction of defect centers surroundings induced by illumination. # 2001 Elsevier Science B.V. All rights reserved.

Gallium-induced deep level in Pb1−xGexTe alloys

Galvanomagnetic properties of gallium-doped Pb1−xGexTe (0.04≤x≤0.08) alloys were studied. It is shown that gallium doping induces a deep impurity level in the alloy band gap; the energy position of this level depends on the germanium content in the alloy. A model assuming that doping with gallium results in the emergence of two defect levels in the energy spectrum of the alloys is proposed.