V. I. Okulov

Effects of resonance scattering of electrons by donor impurities in semiconductors

A generalized formulation of the Friedel approach is given and a theoretical description of the effects of resonance scattering of conduction electrons by donor impurities in semiconductors is developed. The stabilization of the electron density when the Fermi energy reaches the resonance level and the temperature and concentration dependences of the electron mobility and magnetic susceptibility of the localized resonance states are considered in detail. The limits of applicability of the results are discussed.

Low-temperature effects of resonance electronic states at transition-element impurities in the kinetic, magnetic, and acoustic properties of semiconductors

New research results on phenomena due to the existence of electronic resonance energy levels and hybridized states at impurities of transition elements in semiconductors are presented. The data show that the thermal conductivity and ultrasonic parameters of mercury selenide containing iron impurities have resonance anomalies due to the influence of these impurities. A consistent and detailed interpretation is offered for the set of observed effects of hybridized states in mercury selenide with iron impurities. The proposed interpretation of the data obtained on other systems is discussed.

Low-temperature anomalies of the mobility and Shubnikov–de Haas oscillations due to electron resonance scattering on donor impurities in semiconductors. Explanation based on the Friedel approach

Manifestations of electron resonance scattering by donor impurities in the low-temperature conductivity of semiconductors are investigated in the case when the donor resonance energy level of the impurities lies in the conduction band. It is shown that the application of resonance scattering theory in the framework of the Friedel approach can explain the stabilization of the electron density, the maximum of the electron mobility, and the minimum of the Dingle temperature as a function of the concentration of donor impurities and also the anomalous temperature dependence of the mobility due to the resonance. New experimental data are obtained on the concentration, mobility, and Dingle temperature of electrons in mercury selenide crystals containing iron impurities, and it is found that these new results, like those known previously, are in complete agreement with the behavior predicted in the proposed approach. The relation of this approach to the previous interpretation of the concentration maximum of the...

Experimental study of manifestations of resonance scattering of conduction electrons on transition-element impurities in mercury selenide

An interpretation of the experimental data on the low-temperature conductivity and magnetic susceptibility of mercury selenide containing donor impurities of transition elements is developed on the basis of electron resonance scattering theory in the Friedel approach. Both existing data and results obtained in the present study, for solid solutions of chromium, cobalt, and gadolinium, are considered. The results of a fitting of the measured temperature dependence of the electron mobility in HgSe:Cr crystals and concentration dependence of the Curie constant in the impurity magnetic susceptibility of HgSe:Co crystals are analyzed to obtain quantitative confirmation of the idea that resonance donor levels of the impurities chromium and cobalt are present in the conduction band of the respective crystals. The resonance level widths are determined and are found to be an order of magnitude larger than those of iron. It is shown that the observed concentration maximum of the electron mobility in mercury selenid...

Anomalous low-temperature contribution to the heat capacity from hybridized electronic states on transition element impurities

An anomalous nonmonotonic contribution to the temperature dependence of the electron heat capacity of mercury selenide is detected. This is explained in terms of hybridized electronic states on donor impurities. The observed effect is described by a theory of electron heat capacity based on a quantum Fermi-liquid approach including localization and electron-electron interactions. A quantitative interpretation of the experimental dependences yields values for the parameters of the hybridized states that are consistent with those known from other experiments. A new parameter characterizing the electron-electron interaction in the hybridized states is also found.

Experimental validation of the anomalies in the electron density of states in semiconductor iron-vanadium-aluminum alloys

The temperature dependences of the resistivity, Hall coefficient, and magnetic susceptibility of iron-vanadium-aluminum alloys have been investigated. It has been established that the alloy Fe1.9V1.1Al exhibits semiconductor behavior for the method used to obtain uniform alloys. It is shown that at temperatures below 30K the semiconductor alloy possesses the characteristic low-temperature scale of the dependences observed, which could be responsible for the appearance of a narrow pseudogap in the electron density of states. A simple theoretical description of the effects of a pseudogap is proposed. A consistent fit of the theoretical to the experimental relations made it possible to determine the effective width of the pseudogap (∼1MeV) and its relative depth (∼102).

Magnetic susceptibility of resonance donor impurities of transition elements in semiconductors

It is shown that in the resonance scattering of electrons on donor impurities of transition elements in semiconductors there is a contribution to the spin susceptibility from the electron density localized at the impurities. The Curie constant due to this has an unusual dependence on the impurity concentration. An expression for the spin susceptibility of resonantly scattered electrons is obtained in the Friedel approach. The experimental data obtained on mercury selenide containing iron impurities confirm the theoretical results and permit determination of the effective spin of the resonance state.

Experimental discovery and theoretical description of the anomalous hall effect in a spontaneously polarized electron system of hybridized impurity states

An anomalous magnetic-field-independent contribution to the Hall resistance of mercury selenide crystals with a small iron impurity has been discovered in room-temperature experiments. This contribution has been shown to be due to spontaneous polarization of the electron system of hybridized impurity states. The theoretical explanation of the effect based on the thermodynamic description of dissipationless electron current in the spontaneously polarized electron system has been proposed.

Experimental observation of spontaneous spin polarization of electrons in hybridized states of transition element impurities in semiconductors

Experimental evidence of the possible existence of spontaneous spin polarization of the electron system in hybridized states formed by transition element impurity atoms in the conduction band of semiconducting crystals is examined. The details of a quantitative interpretation of experiments on the temperature dependence of the specific heat and elastic moduli of mercury selenide crystals with iron impurities confirm the feasibility of establishing the presence of electron spin polarization in this type of experiment, as well as the possible existence of polarization in the crystals studied here. Theoretical arguments support the observation of a thermodynamic anomalous Hall effect owing to spontaneously polarized donor electrons from low-concentration impurities.

Anomalies in the temperature dependence of the contribution to the speed of sound from hybridized electronic states of transition element impurities

The temperature dependence of the speed of sound in crystalline mercury selenide with low concentrations of iron impurities is studied. Experiments are conducted in the ranges of concentration and temperature where hybridized electronic states in iron impurities have been observed previously. It is found that at temperatures below 10 K the speed of slow transverse ultrasonic waves has an anomalous nonmonotonic segment of its temperature variation that is related to the influence of the impurities and reflects the existence of hybridized states. The observed anomalies in the sound speed are described in terms of a theory for the electron contribution to the elastic moduli that includes hybridization of impurity states and electron-electron interactions. Fits of the theoretical dependences to the experimental data yield quantitative information on the parameters of the hybridized states and of the Fermi-liquid interaction.