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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.

The transport properties of n-CdAs2 have been studied under increasing and decreasing hydrostatic (p ≤ 9 GPa) and quasi-hydrostatic (p ≤ 50 GPa) pressures. We have identified three phase transitions in n-CdAs2 and two phase transitions in p-ZnAs2. According to temperature-dependent resistivity data, the conductivity of the materials is determined by activation mechanisms in the temperature range 250–400 K, with a temperature-dependent activation energy. We have obtained pressure dependences of the activation energy and coefficient R 0, which characterizes the carrier mobility, concentration, and effective mass.

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.

This paper presents the results of the high pressure (up to 7 GPa) effect on the diluted magnetic semiconductor (DMS) CdGeAs2: Mn with x = 0.06–030. The normal R0 and anomalous RS portions of the Hall coefficients have been determined from the magnetic field dependencies of the Hall resistance. Pressure ranges related to the anomalies of the electric and magnetic properties have been found and studied. It has been shown that structural phase transitions are observed on the baric dependencies and their transition point shifts depending on the Mn content. The first- and second-order phase transitions (ferromagnetic–paramagnetic and paramagnetic–paramagnetic) have been identified on the magnetic susceptibility dependence in the pressure areas of P > 1.3 GPa and P ≈ 4 GPa which can be explained by occurrence of the second phase of MnAs in the basic structure of CdGeAs2. Positive (PMR) and negative magnetoresistance (NMR) induced by high pressure also takes place in all the compounds studied.

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.

The resistivity (ρ) and Hall coefficient (RH) of n-Cd1 − xCoxGeAs2 with x = 0.05–0.15 were measured as functions of temperature (at atmospheric pressure) and pressure (up to p = 7 GPa). The temperature-dependent ρ data were used to determine the ionization energy of a cobalt-related impurity center. In the ρ(p) and RH(p) curves, we identified structural semiconductor-semiconductor phase transitions under both increasing and decreasing pressure. Using a mixed-phase structure-effective medium model, we assessed the dynamics of the variation of phase composition with pressure.

The structural and magnetic phase transitions and magnetoresistance of the diluted magnetic semiconductors Cd1 − xMnxGeAs2 and Cd1 − xMnxGeP2 have been studied at high hydrostatic pressures, up to 7 GPa. The normal and anomalous Hall coefficients of the samples have been determined graphically from experimental data.

Cd0.81Mn0.19GeP2 dilute magnetic semiconductor (DMS) has been subjected to a complex study of electric and magnetic properties under high hydrostatic pressures of up to 7 GPa with pressure rise and release. Electrical resistivity, Hall factor, transverse magnetoresistance, relative magnetic susceptibility, and volume magnetostriction have been measured. Compressibility (k) and spontaneous magnetization coefficient (ωS) have been calculated.

We have studied the effect of high pressures on the electrical and magnetic properties of dilute magnetic semiconductor Cd0.82Mn0.18GeAs2. Electrical resistivity, Hall coefficient, transverse and longitudinal magnetic resistance, and magnetic susceptibility have been measured under high pressures (up to 9 GPa). The energy of a manganese impurity level was estimated at 155 meV from electrical resistivity and Hall factor versus temperature curves at the atmospheric pressure. Structural and magnetic phase transitions have been discovered in Hall resistance versus magnetic field curves measured at various temperatures; abnormal and normal Hall factors have been calculated.

In CdGeAs2 , a metamagnetic phase transition and a negative magnetic resistance induced by high pressure were found and studied.

The ferromagnetic semiconductor Cd0.7Mn0.3GeAs2 undergoes a high-pressure ferromagnetic-to-antiferromagnetic phase transition. We have studied this transition at different temperatures. From magnetic-field dependences of the Hall resistance measured at different temperatures, we have derived the normal and anomalous Hall coefficients of the material as functions of temperature. Its transverse magnetoresistance changes from positive to negative near the ferromagnetic-to-antiferromagnetic phase transition.

The electrical resistivity and Hall coefficient of oriented single-crystal p-Cd1 − xMnxGeAs2 samples have been measured at high pressures. The results indicate that the crystals undergo a reversible structural transformation at 5.5 GPa, which is independent on the sample orientation.

The electrical resistivity and Hall factor in n-CdAs2, p-ZnAs2, and n-CdxZn1 − xAs2 were measured at hydrostatic pressures up to 9 GPa and quasi-hydrostatic pressures up to 50 GPa at room temperature. For n-CdAs2, a phase transition was discovered at p = 5.5 GPa; for p-ZnAs2, two phase transitions were discovered: one at P = 10–15 GPa and the other at p = 35–40 GPa. No anomalies were found on ρ(p) and R(p) curves for CdxZn1 − xAs2 when p ≤ 9 GPa.

The dependencies of resistivity ρ and Hall coefficient R H on hydrostatic pressure up to 9 GPa have been investigated for the two semiconductor materials: CdSnAs2 and InAs. The series of CdSnAs2 samples has n∼ 1016 cm−3 (for those doped with Cu) and n∼ 1018 cm−3 (for undoped) of electron concentration. The InAs undoped sample has n∼ 1016 cm−3. For all CdSnAs2 samples, a polymorphous phase transition takes place at P∼ 4.2 GPa. This transition is accompanied with the decomposition of initial compound. In InAs, the polymorphous phase transition is reversible: after decompression the initial composition is the same. The analysis of ρ (P) in both CdSnAs2 and InAs, points out on the existence of quasi-localized energy levels deep in conduction band.

Electrical resistivity and Hall coefficient in the samples of Cd1−xMnxGeP2, where x=0÷ 0.19, have been measured under hydrostatic pressures up to 5 GPa. All measurements were carried out at T=300 K. A dissociation of Cd1−xMnxGeP2 solid solution was observed and the formation of separated phases of CdP2 and Ge were found at P=3.2 GPa for the Mn fraction x

Temperature (for T = 77–400 K) and pressure (for P ≤ 8 GPa) dependences of conductivity σ(T,P). Hall coefficient R H(T, P), and Seebeck coefficient Q(T) were studied in single-crystal n-ZnO samples with the impurity concentration N i = 1017 − 1018 cm−3 and free-electron concentration n = 1013−1017 cm−3. Single crystals were grown by the hydrothermal method. Dependence of the ionization energy of a shallow donor level on the impurity concentration E d1(N d) is determined, along with the pressure coefficients for the ionization energy ∂E d1/∂P and static dielectric constant ∂x/∂P. A deep defect level with the energy E d2 = 0.3 eV below the bottom of the conduction band is found. The electron effective mass is calculated from the obtained data on the kinetic coefficients R H(T) and Q(T).

The electrical resistivity and Hall coefficient of Cd1−xMnxGeP2 (x=0−0.19) have been measured at 300 K and hydrostatic pressures of up to 5 GPa. The results indicate that CdGeP2 dissociates to CdP2 and Ge at p = 3.2 GPa, while the incorporation of manganese stabilizes the crystal structure of CdGeP2, and Cd0.81Mn0.19GeP2 undergoes a reversible phase transition at p = 3.5 GPa.

Pressure-dependent resistivity and Hall effect measurements indicate that p - type Cd1 - xMnx GeAs2 solid solutions with x = 0.06 and 0.18 undergo a high-pressure semiconductor-metal transition. The characteristic points of the phase transition are located, and its dynamics is analyzed in terms of the theory of mixed-phase systems.

The effect of pressure on electrical properties of Ga-doped n-Pb1−xGexTe alloys (x=0.06, 0.08) is studied. The pressure dependence of the activation energy of a deep Ga impurity center is obtained. It is shown that the position of the Ga level with respect to the bottom of the conduction band is virtually unchanged under pressure. Anomalies are found in the temperature and pressure dependences of the resistivity; these anomalies are apparently associated with structural phase transitions from the cubic to the rhombohedral and orthorhombic phases, respectively. The results obtained are used to construct a diagram of the modification of the energy spectrum of charge carriers in the cubic phase of the alloys investigated under pressure.

Room-temperature ferromagnetism in Mn-doped chalcopyrites is a desire aspect when applying those materials to spin electronics. However, dominance of high Curie-temperatures due to cluster formation or inhomogeneities limited their consideration. Here we report how an external perturbation such as applied hydrostatic pressure in CdGeP₂:Mn induces a two serial magnetic transitions from ferromagnet to non-magnet state at room temperature. This effect is related to the unconventional properties of created MnP magnetic clusters within the host material. Such behavior is also discussed in connection with ab initio density functional calculations, where the structural properties of MnP indicate magnetic transitions as function of pressure as observed experimentally. Our results point out new ways to obtain controlled response of embedded magnetic clusters.

Specific electroresistance and Hall coefficient on oriented ZnAs 2 and CdAs 2 single crystals in the region of room temperatures at hydrostatic pressure up to 9 GPa were measured. In p -ZnAs 2 specific electroresistance falls for one order of magnitude with the increase of pressure, and Hall coefficient falls for two orders in magnitude, and at P =7 GPa specific electroresistance and Hall coefficient come out to a saturation. Under mentioned conditions the phase transition in investigated p -ZnAs 2 samples was not observed, in all probability it occurs under the pressure P >10 GPa. Two groups of n -CdAs 2 samples oriented on [1 0 0] and [0 0 1] directions were investigated. The reversible structural phase transition was observed in investigated n -CdAs 2 samples at P =5.5 GPa from the dependencies of specific electroresistance „ ( P ) and Hall coefficient R H ( P ). On the basis of the values of concentrations and mobilities before and after phase transition a conclusion was made that semiconductor-semico...

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.

The magnetic susceptibility and transverse magnetoresistance of p-Cd0.947Mn0.053GeAs2 single crystals have been measured at hydrostatic pressures p < 7 GPa. The crystals are shown to undergo a pressure-induced metamagnetic phase transition and to have a negative magnetoresistance.

The specific volume of the diluted magnetic semiconductor Cd1 − xMnxGeAs2 (x = 0.06–0.3) has been determined for the first time by strain measurements at pressures of up to 7 GPa. From the pressure dependences of the relative specific volume, we evaluated the volume magnetostriction (spontaneous magnetization coefficient). A scaling relation was used to estimate the bulk modulus of the magnetically ordered and disordered phases.

The electrical resistivity and Hall coefficient of n-type CdAs2crystals cut along [001] and [100] were measured at hydrostatic pressures in the range 0–9 GPa. The ρ(P) and RH(P) curves for the [001] direction show three peaks at 1.8, 3, and 5.5 GPa. In the [100] direction, the curves show two peaks at 3 and 5.5 GPa. The peaks at 1.8 and 3 GPa are likely related to impurity levels. The peak at 5.5 GPa is due to the phase transition of CdAs2 . The parameters of the phase transition are determined.

Resistivity ρ and the Hall coefficient R H at atmospheric pressure in the temperature range of 77–400 K and the dependences of these parameters (ρ(P) and R H(P)) and magnetic susceptibility (χ(P)) on hydrostatic pressures of up to P ≤ 7 GPa at 300 K in p-InAs〈Mn〉 single crystals was investigated. The baric coefficients of the ionization energy of Mn impurity centers and the pressure dependence of the dielectric constant ɛ(P) were determined.

The resistivity, Hall coefficient, and magnetoresistance ratio of the ferromagnetic semiconductor Cd0.7Mn0.3GeAs2 have been measured as functions of pressure, temperature, and magnetic field. The ρ(p) and RH(p) curves point to a structural insulator-metal phase transition under both increasing and decreasing pressure. The temperature dependences of ρ and RH show anomalies, which are interpreted as a ferromagnetic-paramagnetic phase transition. Cd0.7Mn0.3GeAs2 is shown for the first time to have a negative magnetoresistance under pressure.

The magnetic susceptibility χ/χ0 and the longitudinal Δρ zz /ρ0 and transverse Δρ xx /ρ0 magnetoresistances have been measured as functions of the hydrostatic pressure P ≤ 7 GPa at room temperature in the high-temperature ferromagnetic semiconductor Cd0.7Mn0.3GeAs2 with a chalcopyrite structure and the Curie temperature T c = 355 K. A pressure-induced metamagnetic transition from the low-magnetization state to the high-magnetization state has been observed in Cd0.7Mn0.3GeAs2 near the magnetic ordering temperature. This transition is accompanied by the hysteresis of the magnetic susceptibility and magnetoresistance.

The baric (P ≤ 5GPa) and magnetic-field (H ≤ 5 kOe) dependences of the transverse magnetore-sistance Δρxx/ρ0 have been measured for p-InAs (RH = 22.5 cm3/C, ρ = 0.15 Ω cm) and the new ferromag-netic semiconductor p-CdGeAs2 (RH = 5 cm3/C, ρ = 0.62 Ω cm), doped with a magnetic impurity (Mn), near the temperature T = 297 K. The dependences Δρxx/ρ0 (P, H) for p-InAs:Mn and p-CdGeAs2:Mn exhibit a magnetoresistive effect with an increase in pressure, and a pressure-induced magnetoresistance hysteresis is observed in p-CdGeAs2:Mn with a pressure drop.

The pressure dependences of the resistivity p(P) and Hall coefficient R P (P) have been measured for heavily doped Cd 0.7 Mn 0.3 GeAs 2 at increasing and decreasing pressure at room temperature. To investigate temperature properties of conductivity in Cd 0.7 Mn 0.3 GeAs 2 , the temperature depend-ences ρ(T) and R P (T) have been defined in the temperature range 77-450 K at atmospheric pressure. The pioneering measurements of magnetoresistance Δρ xx (H,P)/ρ 0 (P) in Cd 0.7 Mn 0.3 GeAs 2 are presented. A hysteresis of magnetoresis-; tive effect has been. found when pressure rises and falls.

The room-temperature electrical resistivity and Hall coefficient of [001]- and [010]-oriented CdSb single crystals are measured as functions of increasing (up to 7 GPa) and decreasing pressure. Some parameters of the high-pressure phase transformation in CdSb are evaluated from experimental data, and the fraction of the low-pressure phase is calculated as a function of pressure. The parameters of the phase transformation are shown to depend on the crystal orientation.

The effect of hydrostatic pressure on resistivity and magnetic ac susceptibility has been studied in Mn-doped CdGeAs2 room-temperature (RT) ferromagnetic chalcopyrite with two types of MnAs micro-clusters. The slight increase of temperature by about 30 K in the region between RT and Curie temperature TC causes a significant change in the positions of pressure-induced semiconductor-metal transition and magnetic phase transitions in low pressure area. By conducting measurements of the anomalous Hall resistance in the field H \leq 5 kOe, we present experimental evidence for pressure-induced metamagnetic-like state during the paramagnetic phase at pressure P = 5 GPa.

Kinetic effects in p-ZnAs2 were measured at hydrostatic (P ≤ 9 GPa) and quasi-hydrostatic (to P ≤ 50 GPa) pressures on pressure buildup and depressurization. A conclusion on the occurrence of two phase transitions was made: I-II at P = 9-15 GPa and II-III at P = 30-35 GPa. Based on the temperature dependences of electrical resistance, it was shown that the conductivity is determined by activation mechanisms in a temperature range of 250-400 K; in this case, the activation energy changed with temperature and pressure. The pressure dependences of the activation energy and the coefficient R 0, which characterizes the mobility, concentration, and effective mass of carriers, were calculated. © 2013 Pleiades Publishing, Ltd.

The electrical properties of n-type Cd0.97Zn0.03As2 and Cd0.95Zn0.05As2 single crystals are studied at hydrostatic pressures of up to 9 GPa. With increasing pressure, the carrier concentration in the solid solutions increases by more than three orders of magnitude, while their electrical resistivity drops by more than four orders of magnitude. In contrast to CdAs2 , the pressure dependences of resistivity for the solid solutions show no anomalies, which is interpreted as evidence that Zn consolidates the structure of CdAs2 , occupying vacant As sites.

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.

The dependences of the longitudinal magnetoresistance (Δρzz/ρ0)(P), transverse magnetoresistance (Δρxx/ρ0)(P), and magnetic susceptibility (χ/χ0(P)) on hydrostatic pressure P ≤ 7 GPa in the ferromagnetic semiconductor Cd0.7Mn0.3GeAs2 at room temperature were investigated.

We present the experimental results of the effect hydrostatic pressure up to P ≤ 7 GPa applied at the room temperatures in diluted magnetic semiconductor Cd1−xMnxGeAs2 (x = 0.06 − 0.3). We have found the pressure areas at which anomalies in magnetic properties were observed. Induced by hydrostatic pressure at P > 1.5 GPa magnetic phase transitions, interpreted as metamagnetic transition, were observed. The transitions from magnetic-ordered into magnetic disordered phases in region P > 4.1 GPa on the pressure dependences of relative volume compressibility were detected. We estimated the values of bulk modulus and volume magnetostriction. It is shown that high pressures significantly decrease the Curie temperature with values dTC/dP ≈ (−14.0 ÷ −6.8) K/GPa.

The electrical properties of ZnAs2 single crystals were measured along the [001] direction in the pressure range from 0 to 9 GPa. The electrical resistivity of the crystals was found to decrease by one order of magnitude as the pressure increases from 0 to 7 GPa, without significant changes at higher pressures. The Hall coefficient drops by two orders of magnitude as the pressure increases from 0 to 7 GPa and remains constant in the range from 7 to 9 GPa.

Pressure dependences of resistivity ρ(P) and Hall coefficient RH have been measured for the novel high-temperature ferromagnetic semiconductor p-Cd1-xMnxGeAs2 (x=0÷0.36) at the room temperature. Structural phase transitions with positions shifting towards low pressures, when percentage of manganese increases from 5.9 GPa for CdGeAs2 to 4.8 GPa for p-Cd0.64Mn0.36GeAs2, are found out. Some anomalies of dependence RH(P), which we attribute to magnetic properties and the presence of impurities, are found out for the crystals with the greater percentage of manganese (x≥0.18).