A. T. Lonchakov

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.

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.

Nanoscale distortions of the lattice of a ZnSe crystal doped with 3d elements

The structure of semiconductor crystals Zn1−xVx2+Se (x = 0.0018) and Zn1−xCrx2+Se (x = 0.0006) was studied for the first time using thermal neutron diffraction at 300 and 120 K. The diffraction patterns of the crystals were revealed to contain diffuse scattering regions near the Bragg reflections of the initial cubic lattice. The experimental results are discussed in combination with earlier obtained data on neutron diffraction and propagation of ultrasonic waves in Zn1−xNix2+Se (x = 0.0025) and Zn1−xCrx2+Se (x = 0.0029). The diffuse scattering is shown to be due to nanoscale shear strains of the ZnSe lattice. The character of these strains is determined by Jahn-Teller 3d ions.

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.

Ultrasonic investigation of a phase transition in ZnSe:Ni

Ultrasonic experiments on ZnSe and ZnSe:Ni crystals with impurity concentrations of 5.5×1019 cm−3 have revealed precursor phenomena at temperatures much higher than the temperature of the structural transition (Tc=14.5 K). It is found that the elastic constant C44 softens while C11 and C12 become stiffer as Tc is approached from above; the strains associated with the order parameter are transverse deformations of the e4 type. A brief symmetry analysis of the possibilities of formation of a tetragonal phase is given. The Jahn–Teller effect and displacement of the charge density on the chemical bonds are discussed as probable causes of the low-temperature phase transition.

Ultrasonic investigations of the Jahn–Teller effect in a ZnSe:Fe2+ crystal

The temperature dependence of the absorption and velocity of transverse ultrasonic waves propagating in the [110] direction in a ZnSe:Fe2+ crystal with the iron impurity of n=2.2×1019cm−3 is investigated in the temperature interval 1.4–100K at a frequency of 53MHz. For the slow transverse mode an absorption peak at 7.3K and a decrease of the phase velocity below 40K are found, while no such features are observed for the fast mode. The anomalies are interpreted as manifestations of the Jahn–Teller effect. The softening of the elastic modulus (C11–C12)∕2 indicates that the local distortions in ZnSe:Fe2+ are tetragonal. Under the assumption that the absorption maximum is of a relaxational nature, the temperature dependence of the relaxation time is recovered from the data, and the values of the potential barrier height and vibronic frequency are obtained.

Low-temperature manifestations of hybridized electronic states of iron impurities in the thermoelectric power of mercury selenide

The temperature dependence of the Seebeck coefficient (thermoelectric power) of mercury selenide with iron and cobalt impurities is investigated at low temperatures. In crystals with iron impurities at concentrations close to those corresponding to the concentration maximum of the electron mobility, an anomalously strong decrease of the thermoelectric power is observed in a temperature interval below 25K. This decrease is attributed to a manifestation of resonance scattering of electrons in hybridized states at the iron donor impurities. A fitting of the theoretical temperature dependence to the experimental data permits a quantitative interpretation of the experimental results and yields values of the parameters of the hybridized states which agree with those found from investigations of other effects. In crystals with cobalt impurities no anomalies due to manifestations of hybridized electronic states are observed. This finding is in agreement with the conductivity data and implies a lower value of the ...