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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.

AIIBiνC2V semiconductors doped with Mn are perspective materials for spintronic. Structural, chemical and magnetic properties of these materials have been analyzed. The combinations of these compounds with the traditional semiconductors are perspective to create "system on chip" devices. The coexistence of ferromagnetic and paramagnetic phases was observed. The ferromagnetic phase is likely due to the presence of MnAs nanoclusters (3-5 nm). Paramagnetic properties appear due to Mn complexes (dimmer and trimmer).

It has been demonstrated by a combination of physical and chemical methods that InSb and MnSb form an eutectic (6.5 mol % MnSb, Tm = 513°C). A composition consisting of a [110] oriented InSb single crystal matrix and faceted single-crystal MnSb inclusions has been grown by the Bridgman method. The composition shows pronounced electrical conductivity anisotropy. The electrical conductivity along needle-like MnSb inclusions is 5 times higher than the electrical conductivity in the perpendicular direction. The composition possesses magnetic properties and has a Curie temperature of ∼600 K. The material is of interest as a substrate for ferromagnet/semiconductor heterostructures.

Based on Mn-doped chalcopyrites CdGeAs 2 , ZnGeAs 2 and ZnSiAs 2 the new dilute magnetic semiconductors with p-type conductivity were produced. Magnetization, electrical resistivity, magnetoresistance and Hall effect of mentioned compositions were studied. Their curves of temperature dependence of magnetization have the similar form in spite of complicated character, for which the concentration and mobility of the charge carriers are responsible. Thus, for T T >15 K for a frustrated ferromagnetics. In compounds with Zn these two states dilute by spinglass-like state. This specific feature is assigned to an attraction of Mn ions occupying neighboring sites and to the competition between the carrier-mediated exchange and superexchange interactions. Curie temperatures of these compounds are above room temperature. These are the highest Curie temperatures in the A II B IV C V 2 :Mn systems.

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.

The magnetic properties of a Cd1−xMnxGeAs2: MnAs hybrid micro-composite have the signature of ferromagnetic order at room temperature. Magnetotransport reveals the presence of a large linear positive magnetoresistance, with maximum values of about 550% ( B = 22 T) for x = 0.028 . This is interpreted in terms of an effective medium approximation with the value and the shape of the magnetoresistance depending on the structural and electronic properties of the semiconductor rather than on its magnetic properties. The absence of an anomalous Hall effect leads to the conclusion that ferromagnetic ordering is not the only factor necessary for the occurrence of asymmetric scattering in granular ferromagnetic materials.

The systematic studies of both magnetic and magnetotransport properties of Zn 0.947 Mn 0.053 GeAs 2 diluted magnetic semiconductor are presented. The paramagnetic behaviour of the sample confirms that the solubility of Mn in the studied alloy is of the order of 5 at%. The Curie―Weiss behaviour of magnetic susceptibility is preserved only at low temperatures, T < 100 K indicating the presence of short-range magnetic interactions in the system due to the presence of groups of Mn counting few ions. The high-field magnetization together with magnetoresistance data is used to estimate the amount of magnetic ions active in the semiconductor matrix. The obtained results showed that the amount of magnetically active Mn ions in the semiconductors matrix is two orders of magnitude lower than the value obtained from X-ray fluorescence measurements. The magnetotransport studies revealed that only about 30% of all Mn ions are electrically active in the semiconductor matrix.

Based on the Mn-doped chalcopyrites CdGeAs2, ZnGeAs2 and ZnSiAs2, new dilute magnetic semiconductors with the p-type conductivity were produced. Magnetization, electrical resistivity and Hall effect of these compositions were studied. Their temperature dependences of magnetization are similar in form in spite of a complicated character, which is controlled by the concentration and mobility of the charge carriers. Thus, for T < 15 K, these curves are characteristic of superparamagnets and for T > 15 K, of a frustrated ferromagnet. In compounds with Zn these two states are diluted by a spinglass-like state. This specific feature is ascribed to attraction of Mn ions occupying neighboring sites and to competition between the carrier-mediated exchange and superexchange interactions. The Curie temperatures of these compounds are above room temperature. These are the highest Curie temperatures in the AIIBIVCV2:Mn systems.

The heterostructure ferromagnetic/semiconductor ZnSiAs2/Si was obtained by using the Si-ZnAs2 phase diagram. The magnetic properties of Zn1-XMnXSiAs2 bulk crystals and ferromagnetic layered heterostructures were similar. The same method was used for preparing a ferromagnetic layer ZnGeAs2 on a germanium substrate.

The results of studying phase equilibria of ternary AIIBIVCV systems have been reported. Physicochemical foundations have been developed for the synthesis of new ferromagnets with Curie temperatures above room temperature structurally compatible with basic semiconducting materials. Methods of synthesis and physicochemical properties of manganese-doped AIIBIVC 2 V ferromagnets have been described. The results of theoretical simulation of magnetic properties have been considered and basic approaches to the explanation of the emergence of ferromagnetism in AIIBIVC 2 V doped with 3d metals have been surveyed. The most promising ways to produce and study dilute magnetic semiconductors as spintronics materials have been presented.

New diluted magnetic semiconductors (CdGeAs2:Mn, ZnGeAs2: Mn, and ZnSiAs2: Mn chalcopyrites) were synthesized. Magnetization M, electrical resistivity, magnetoresistance, and the Hall effect of these compositions were examined. Although the M(T) curves are complicated, they are similar in shape, for which the concentration and mobility of the charge bearers. Their Curie points are higher than 300 K, the highest in systems of the AIIBIVC2V: Mn type.

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 Si-ZnAs2 pseudobinary join of the Zn-Si-As system has been studied using physicochemical characterization techniques. It contains a congruently melting compound of composition ZnSiAs2 and has two eutectics: Si-ZnSiAs2, at 55 mol % Si + 45 mol % ZnAs2, with the melting point at 1010°C, and ZnSiAs2-ZnAs2, at 93 mol % ZnAs2 + 7 mol % Si, melting at 730°C. The solubilities of the end-members in ZnSiAs2 are within 1 mol %.

A new p -type dilute magnetic semiconductor was synthesized on the basis of manganese-doped ZnSiAs 2 chalcopyrite. As the manganese percentage in ZnSiAs 2 increased, the Curie temperature increased from 325 to 337 K for compositions containing 1 and 2 wt % manganese. The ferromagnetic properties of the new dilute magnetic semiconductor were due to nanoclusters that were generated by concurrent substitution of manganese for elements in the cationic sublattice of chalcopyrite.

Based on Mn-doped chalcopyrite ZnSiAs2 the new dilute magnetic semiconductor with p-type conductivity was produced. The Curie temperature behavior of the produced semiconductor is distinctly dependent on the Mn concentration: 325 K for 1 wt.% and 337 K for 2 wt.% of Mn, consequently. Magnetization, electrical resistance, magnetic resistance and Hall effect of mentioned compositions were studied. Temperature dependence of magnetization M(T) have complicate behavior. For T  15 K the M(T) dependence is characteristic for superparamagnetic and at T > 15 K magnetization is sum of magnetizations of ensemble of superparamagnetic clusters and ferromagnetic phase contained frustration regions.

A new spintronics material with the Curie temperature above room temperature, the ZnSiAs2 chalcopyrite doped with 1 and 2 wt % Mn, is synthesized. The magnetization, electrical resistivity, magnetoresistance, and the Hall effect of these compositions are studied. The temperature dependence of the electrical resistivity follows a semiconducting pattern with an activation energy of 0.12–0.38 eV (in the temperature range 124 K ≤ T ≤ 263 K for both compositions). The hole mobility and concentration are 1.33, 2.13 cm2/V s and 2.2 × 1016, 8 × 1016 cm−3 at T = 293 K for the 1 and 2 wt % Mn compositions, respectively. The magnetoresistance of both compositions, including the region of the Curie point, does not exceed 0.4%. The temperature dependence of the magnetization M(T) of both compositions exhibits a complicated character; indeed, for T ≤ 15 K, it is characteristic of superparamagnets, while for T > 15 K, spontaneous magnetization appears which correspond to a decreased magnetic moment per formula unit as compared to that which would be observed upon complete ferromagnetic ordering of Mn2+ spins or antiferromagnetic ordering of spins of the Mn2+ and Mn3+ ions. Thus, for T > 15 K, it is a frustrated ferro- or ferrimagnet. It is found that, unlike the conventional superparamagnets, the cluster moment μc in these compositions depends on the magnetic field: ∼12000–20000μB for H = 0.1 kOe, ∼52–55μB for H = 11 kOe, and ∼8.6–11.0μB at H = 50 kOe for the compositions with 1 and 2 wt % Mn, respectively. The specific features of the magnetic properties are explained by the competition between the carrier-mediated exchange and superexchange interactions.

Bulk and film samples of manganese-doped zinc-silicon diarsenide are obtained. Investigation of electrical and magnetic properties of ZnSiAs2: Mn samples showed that they possess the combination of ferromagnetic and semiconductor properties at above room temperature and are of interest as materials for spin transport.

GaN-based photodetectors are of great interest for applications involving detection and imaging in the UV-visible wavelength range. Most of experimental and theoretical work in this area has been focused so far on Schottky diode and p-i-n structures for solar blind applications. However, it seems that bipolar phototransistors with their additional functionality could also be of potential interest. In this work we present the results of phototransistors parameters simulation using the software – Sim Windows. The structure analyzed consisted, counting from the substrate, of n-Al[x]Ga1 – [x]N collector, p-GaN base and n-Al[x]Ga1 – [x]N emitter. The Al mole fraction in the collector and emitter was varied from x = 0.2 to x = 0.3. The collector and emitter thickness was taken as 0.9 hm. The doping level in the emitter and collector was varied from 1017 to 1019 cm – 3. The p-GaN base thickness was taken as 0.3 m, with doping of 1017-1018 cm – 3. The electron and hole lifetimes in the base were taken as 12 ns.

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 the high-temperature ferromagnetic semiconductor p-Zn1 − xCdxGeAs2〈Mn〉 have been measured as a function of pressure near room temperature. The features in the curves obtained attest to a structural phase transition at particular pressures. With increasing manganese content, the phase transition shifts to lower pressure. The features observed in the pressure-dependent Hall coefficient of the crystals containing more than 0.06 wt % manganese, in which ferromagnetic behavior is more pronounced, are probably due to the anomalous component of the Hall effect and its modulation in the presence of narrow impurity bands.

Mn-doped ZnSiAs2/Si heterostructures were grown by vacuum-thermal deposition of ZnAs2 and Mn layers on Si substrates followed by annealing. The surface contained a ZnSiAs2 film, but also micro-crystals with a composition close to ZnAs2 or ZnSiAs2-Si-SiAs eutectic. The temperature and field dependencies of the magnetization were measured. Two types of magnetic phases were detected: a paramagnetic one with the mean magnetic moment of 7.6 Bohr magnetons, formed by Mn2+ ions, and a ferromagnetic one with Curie temperature 340 K in 50 kOe magnetic field, formed by MnAs clusters. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Positron annihilation spectroscopy is used to study point defects in Zn/1-x/Mn/x/GeAs/2/ crystals with low Mn content 0 < x < 0.042 with disordered zincblende and chalcopyrite structure. The role of negatively charged vacancies and non-open-volume defects is discussed with respect to the high p-type conductivity with carrier concentration 1E19 < n < 1E21 cm^-3 in our samples. Neutral As vacancies, together with negatively charged Zn vacancies and non-open-volume defects with concentrations around 1E16-1E18 cm^-3, increasing with the amount of Mn in the alloy, are observed. The observed concentrations of defects are not sufficient to be responsible for the strong p-type conductivity of our crystals. Therefore, we suggest that other types of defects, such as extended defects, have a strong influence on the conductivity of Zn1-xMnxGeAs2 crystals., 8 pages, 3 figures

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.

We present the studies of structural, transport and magnetotransport properties of [Formula: see text]Cd x GeAs2 crystals with the chemical content changing from 0 to 1. The structural studies indicate that this alloy exists as a composite two-phase material in almost the entire range of average chemical compositions. The two phase nature of our samples does have a significant influence on the carrier transport and magnetotransport of the composite alloy. The change of the conductivity type is observed at room temperature, from p-type for [Formula: see text] to n-type for x > 0.18, respectively. The Hall carrier mobility measured at room temperature decreases as a function of x from about 35 cm2 (V · s)-1 for the sample with x = 0 down to 3 cm2 (V · s)-1 for the sample with x = 0.233. For x > 0.233 the Hall carrier mobility shows an increase with x, up to the highest value around 875 cm2 (V · s)-1 observed for the sample with x = 1. Temperature dependent resistivity measurements indicate the presence of thermal activation of carriers with activation energy, E a, with values from 20 to 30 meV for all the studied samples. The temperature dependent Hall effect data show that the grain boundary limited transport is strong in all our samples. For the samples with [Formula: see text] the negative MR is observed at temperatures lower than 100 K and at low magnetic field values, [Formula: see text] T. This effect is interpreted as a weak localization phenomenon with low values of phase coherence length, [Formula: see text] nm.

We present studies of structural, magnetic, and electrical properties of Zn1-x Mn x SnSb2+MnSb nanocomposite ferromagnetic semiconductors with the average Mn-content, [Formula: see text], changing from 0.027 up to 0.138. The magnetic force microscope imaging done at room temperature shows the presence of a strong signal coming from MnSb clusters. Magnetic properties show the paramagnet-ferromagnet transition with the Curie temperature, T C, equal to about 522 K and the cluster-glass behavior with the transition temperature, T CG, equal to about 465 K, both related to MnSb clusters. The magnetotransport studies show that all investigated samples are p-type semiconductors with high hole concentration, p, changing from 10(21) to 10(22) cm(-3). A large increase in the resistivity as a function of the magnetic field is observed at T

Computer simulations were performed to increase the quantum efficiency of LED by optimizing the nanoheterostructure (NH). Furthermore, the InGaN and AlGaP NHs for LEDs were optimized. On the basis of the optimum NH, ways to further increase the efficiency and the influence of impurities and indium atoms doped into barriers between quantum wells were investigated. The optimum impurity and indium atom concentrations to achieve higher flux were determined.

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.

We present studies of structural, magnetic and electrical properties of Zn/1-x-y/Cd/x/Mn/y/GeAs/2/ nanocomposite ferromagnetic semiconductor samples with changeable chemical composition. The presence of MnAs clusters induces in the studied alloy room temperature ferromagnetism with the Curie temperature, TC, around 305 K. The chemical composition of the chalcopyrite matrix controls the geometrical parameters of the clusters inducing different magnetoresistance effects in the crystals. The presence of ferromagnetic clusters in the alloy induces either negative or positive magnetoresistance with different values. The Cd-content allows a change of magnetoresistance sign in our samples from negative (for x = 0.85) to positive (for x = 0.12). The negative magnetoresistance present in the samples with x = 0.85 is observed at temperatures T < 25 K with maximum values of about -32% at T = 1.4 K and B = 13 T, strongly depending on the Mn content, y. The positive magnetoresistance present in the samples with x = 0.12 is observed with maximum values not exceeding 50% at B =13 T and T = 4.3 K, changing with the Mn content, y., 8 pages, 7 figures

We present systematic studies of magnetic and transport properties of Zn1−xMnxGeAs2 semimagnetic semiconductor with the chemical composition varying between 0.053≤x≤0.182. The transport characterization showed that all investigated samples had p-type conductivity strongly depending on the chemical composition of the alloy. The Hall effect measurements revealed carrier concentrations p≥1019 cm−3 and relatively low mobilities, μ≤15 cm2/(V s), also chemical composition dependent. The magnetic investigations showed the presence of paramagnet-ferromagnet phase transitions with transition temperatures greater than 300 K for the samples with x≥0.078. We prove by means of x-ray diffraction, nuclear magnetic resonance, and scanning electron microscopy techniques that the observed room temperature ferromagnetism is due to the presence of MnAs inclusions. The high field magnetoresistance showed the presence of giant magnetoresistance effect with maximum amplitudes around 50% due to the presence of nanosize ferromagnetic grains.

Based on Mn-doped chalcopyrite ZnSiAs2 the new dilute magnetic semiconductor with p-type conductivity was produced. The Curie temperature behaviour of the produced semiconductor is distinctly dependent on the Mn concentration: 325 K for 1 wt.% and 337 K for 2 wt.% of Mn, consequently. Magnetization, electrical resistance, magnetic resistance and Hall effect of mentioned compositions were studied. Temperature dependence of magnetization M(T) have complicate behaviour. For T ≤ 15 K the M(T) dependence is characteristic for superparamagnetic and at T > 15 K magnetization is sum of magnetizations of ensemble of superparamagnetic clusters and ferromagnetic phase contained frustration regions.

Results of investigation of n-type Bi2-xMnxTe3with x≈0.025 grown by the Bridgman method are presented. Structural properties are studied by means of x-ray diffraction, EDX and positron lifetime spectroscopy. Results of AC magnetic susceptibility measurements and electronic magneto-transport measurements show existence of ferromagnetic phase transition at 5.3 K. Effects of the phase transition on the electronic transport properties are studied.