Search

The impurity energy spectrum of undoped n-type GaAs, InAs, CdSnAs2, CdGeAs2, and CdTe, ZnO bulk crystals is studied based on a quantitative analysis of the baric and temperature dependences of the kinetic coefficients. It is found that the deep-level donor center corresponds to the intrinsic vacancy defect in the anion sublattice in the above-listed semiconductors. The conclusion on the nature of the donor center, i.e., the vacancy in the anion sublattice, is based on the fact that, in contrast to shallow impurity centers which trace the intrinsic band under uniform pressure, to which they are genetically related, the energy of deep impurity centers with respect to absolute vacuum remains constant under isotropic compression of the lattice. Therefore, it seems favorable to study the evolution of the carrier energy spectrum in semiconductors under uniform-pressure conditions. The energy-level positions with respect to the conduction-band edge and pressure coefficients of the energy gaps between them and the corresponding conduction-band bottom are determined. The shift of the energy level of the deep donor center to the conduction-band depth with decreasing band gap is observed.

The magnetic susceptibility χ(T) of Zn0.1Cd0.9GeAs2 + n wt % MnAs (n = 10 or 15) ferromagnetic nanocomposites with a Curie temperature TC = 310 K has been measured as a function of temperature in the temperature range 270–350 K, and their resistivity ρ(p), Hall coefficient RH(p), and magnetization M(p) have been measured as functions of pressure near room temperature. The materials have been shown to undergo a pressure-induced ferromagnetic-to-paramagnetic phase transition, accompanied by a semiconductor–metal phase transition, at a hydrostatic pressure p ≈ 3.2 GPa and room temperature.

The effect of high pressure on electron transport and on the field dependence of the transverse magnetoresistance has been studied in a hybrid nanocomposite based on the Zn0.1Cd0.9GeAs2 matrix and MnAs clusters. A record high negative magnetoresistance of ~74% is formed near a pressure-induced structural transition (P≈ 3.5 GPa). The considered scattering mechanisms include both the contribution from MnAs clusters at relatively low pressures (up to 0.7 GPa) and spin-dependent scattering by localized magnetic moments in the Mn-substituted structure of the matrix in the region of the structural transition. The presence of the positive magnetoresistance region associated with the two-band transport model in the high-pressure phase, as well as the large negative magnetoresistance, is described in the framework of the semiempirical Khosla–Fischer expression.

The temperature (T = 77–420 K) dependences of the electrical resistivity and the magnetization, the magnetic-field (H ≤ 5 kOe) and pressure (P ≤ 7 GPa) dependences of the resistivity, the Hall coefficient, and the magnetization have been measured in the Zn0.1Cd0.9GeAs2 + 10 wt % MnAs composite with the Curie temperature T C = 310 K. The magnetoresistive effect has been observed at high hydrostatic pressure to 7 GPa. At nearly room temperature, the pressure dependence of the magnetization demonstrated a transition from the ferromagnetic to paramagnetic state at P ~ 3.2 GPa that was accompanied by the semiconductor–metal phase transition.

The dependences of the electrical resistivity and the Hall coefficient of single-crystal p-InAs〈Mn〉 bulk samples with an acceptor concentration of about 1018 cm–3 on uniform pressure P = 4–6 GPa at T = 300 K in the region of impurity conduction are quantitatively analyzed. The anomalous Hall effect is shown to occur in p-InAs〈Mn〉. Its contribution is negative and correlates with the deionization of acceptors and an increase in the magnetic susceptibility.

In bulk samples of p-Cd1 − x Mn x GeP2, p-Cd1 − x Mn x GeAs2, and p-Zn1 − x Mn x GeAs2 at high hydrostatic pressures (P ≤ 9 GPa), the pressure dependences of the electrical resistivity and the volume change were studied. In all the studied samples, there were phase transitions accompanied by a volume jump. This suggested that the observed phase transition is a pressure-induced structural phase transition.

The effect hydrostatic pressure of up to 9 GPa has on the electrical behavior of polymer composites based on multiwalled carbon nanotubes (MWCNT) is investigated at room temperature. The ratio R9GPa/R0 ≈ 7 for samples with resistance in the kilo-ohm range is higher than for samples in the ohm range. Pressure-induced MWCNT features at P ≈ 1.5 GPa are associated with the deformation of the circular form of nanotube walls, in agreement with theoretical predictions. Measurements of direct and reverse resistance and current voltage characteristics under pressure demonstrate the reversibility of electrophysical properties, which could find practical application in creating pressure sensors.

We have measured the resistivity and relative bulk compressibility of Zn1 − xMnxGeAs2 (x = 0.02 and 0.4) samples at hydrostatic pressures of up to 9 GPa. The pressure dependences of the resistivity and relative compressibility demonstrate sharp changes in resistivity and volume. The changes occur at the same high pressure, attesting to a structural phase transition.

Hydrostatic pressure studies of the isothermal magnetization and volume changes up to 7 GPa of magnetic composite containing MnP clusters in an insulating $\mathrm{CdGe}{\mathrm{P}}_{2}$ matrix are presented. Instead of alleged superparamagnetic behavior, a pressure-induced magnetization process was found at zero magnetic field, showing gradual enhancement in a low-field regime up to $H\ensuremath{\geqslant}5$ kOe. The simultaneous application of pressure and magnetic field reconfigures the MnP clusters with antiferromagnetic alignment, followed by onset of a field-induced metamagnetic transition. An unusual hysteresis in magnetization after pressure cycling is observed, which is also enhanced by application of the magnetic field, and indicates reversible metamagnetism of MnP clusters. We relate these effects to the major contribution of structural changes in the composite, where limited volume reduction by 1.8% is observed at $P\ensuremath{\sim}5.2$ GPa.

A technology of two stage selenezation method in the carrier gas (nitrogen) stream of the reaction component (selenium) has been suggested for the CuIn0.95Ga0.05Se2 thin film growing. Morphology and structure of the CuIn0.95Ga0.05Se2 film have been studied by SEM and XRD methods. Phase compound of film material for the CuIn0.95Ga0.05Se2 semiconductor solution has been studied by X-ray photoelectron spectroscopy method.

An unusual change in the hysteresis direction is believed as rare phenomenon associated with perovskite-type structure. Such 'anomalous' magnetization hysteresis could possess a direct impact on the giant magnetoresistance (MR). Here we demonstrate that the room-temperature magnetization versus pressure for chalcopyrite semiconductor Zn1−x Mn x GeAs2 with x = 0.01 follows a usual direction of hysteresis, while the direction turns into anomalous for x = 0.07. Both these phenomena are results of a pressure-induced structural transition occurring in the host material, as is evident from volumetric measurements and ab initio calculations. This structural transition gives rise to the pressure-enhanced large MR and changes it drastically. Unlike the case of x = 0.01 where MR can be well reproduced within a theoretical approach, the presence of magnetic inhomogeneities for x = 0.07 induces an unexpected crossover from large positive to non-saturating negative MR (~92% at H = 5 kOe) in the new high-pressure phase. These results suggest that Zn1−x Mn x GeAs2 provides an example of a chalcopyrite-based material whose functional possibilities could be expanded through a new type of 'structure-driven' MR.