Growth of epitaxial Cd<Subscript>1–<Emphasis Type="Italic">x</Emphasis> </Subscript>Mn<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>Te films

We have studied the growth and structure of epitaxial films of Cd_1–xMn_x (x = 0.03) diluted magnetic solid solutions grown on mica substrates by molecular beam epitaxy and identified conditions for producing n- and p-type epitaxial films. Using an additional Te vapor source and optimizing the substrate temperature in the growth process, we were able to obtain structurally perfect p-type Cd_1–xMn_xTe (x = 0.03) films with clean, smooth surfaces. The growth plane of the films on the mica substrates is (111) of a face-centered cubic lattice and their unit-cell parameter is а = 6.477 Å.     

Structural Properties of Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Te Solid-Solution Nanoparticles

It is shown that Cd _x Hg_1–xTe solid-solution nanoparticles can be produced by ball milling, but their presence is masked by larger particles. The methods of laser-correlation spectroscopy and X-ray-diffraction analysis have been used to study the structure of the nanoparticles and their size distribution. The presence of a compositional disordering of the solid solution structure was experimentally confirmed.     

Antireflection properties of diamond-like carbon films on Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te (<Emphasis Type="Italic">x</Emphasis> ∼ 0.04) single crystals

The optical properties of diamond-like carbon (DLC) films obtained by plasmachemical deposition on Cd_{1 − x} Zn _x Te (x ∼ 0.04) single crystals have been studied by ellipsometry. The ellipsometric data have been interpreted within the framework of a three-layer model of the DLC film-semiconductor crystal refractory system with transition layers between the film and substrate. It is found that DLC films exhibit antireflection properties in this refractory system in the IR spectral range. It is established that the proposed antireflection film-substrate structure is stable with respect to thermal cycling and ultrasonic treatment.     

Preparation and Properties of Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te

Mn _x Hg_{1 ? x}Te (x = 0.05, 0.12) single crystals were grown by solid-state recrystallization, and their axial and radial homogeneity was assessed by optical, electrical, and electron-microscopic measurements. The crystals are p-type, with a hole concentration of (4.3–5.3) × 10²² m^?3 and Hall mobility in the range (410–570) × 10^?4 m²/(V s).     

Optical and transport properties of Fe-doped Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Se (<Emphasis Type="Italic">x</Emphasis> = 0.35)

The optical and transport properties of Fe²⁺-doped Cd _x Hg_1?x Se crystals with a midgap Fe²⁺ level have been studied. The results demonstrate that Fe²⁺ ions influence both the optical and transport properties of Cd _x Hg_1?x Se〈Fe²⁺〉. The observed optical absorption bands are due to a donor Fe²⁺ level in the band gap, with a depth E _Fe = 0.21 eV, and to band-band transitions. Thermal anneals in Hg and Se vapors have different effects on the carrier concentration and mobility in the crystals. The effect of annealing on the transport properties of the Fe²⁺-doped crystals differs from that for undoped crystals and is governed by the state of point defects.     

Etching of Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te by solutions of the HNO<Subscript>3</Subscript>-HBr-citric acid system

Chemical etching of CdTe single crystals and Zn _x Cd_1?x Te solid solutions by bromine-evolving etchants of the HNO₃-HBr-citric acid system is studied. Projections of the surfaces of equal dissolution rates are plotted; the kinetics of etching processes and the influence exerted on it by the composition of solid solutions and initial concentrations of citric acid are found. The concentration limits of solutions for chemicody-namical polishing of surfaces of the mentioned semiconductors are determined.     

Effect of growth conditions on the compositional homogeneity of Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te crystals

A crystal growth unit has been designed for Cd_{1 − x} Zn _x Te growth by the axial-heat-flux-close-to-the-phase-interface (AHP) method at argon overpressures of up to 12 MPa. The influence of melt superheating, growth rate, melt layer thickness, argon pressure, and growth mode on the Zn distribution in 21- to 45-mm-diameter crystals and defect formation in Cd_{1 − x} Zn _x Te ingots has been investigated. The results demonstrate that the AHP method offers the possibility of effectively controlling the shape of the solid-liquid interface and ensures low fluid velocity and high radial compositional homogeneity. The feeding method used markedly improves the axial Zn profile and ensures low dislocation density (5 × 10³ cm⁻²) in the grown crystal.     

Structural Defects in Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>As<Subscript>2</Subscript> Solid Solutions

The impurity photoconductivity spectra of undoped Cd_{1 ? x} Zn _x As₂ single crystals with x ≤ 0.06 are measured in the range 85–300 K. The results are used to determine the ionization energies of donor and acceptor levels produced in the crystals by structural defects: ?_d ≈ 0.019, 0.26, and 0.42 eV; ?_a = 0.24 and 0.34 eV, respectively. The nature of the structural defects responsible for these levels is discussed.     

Structural and magnetic properties of Cr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te (<Emphasis Type="Italic">x</Emphasis> = 0−0.4) solid solutions

Cr_1?x V _x Te solid solutions with a hexagonal structure (NiAs type) have been obtained in the composition range x = 0?0.4 by direct melting of elemental mixtures, followed by annealing and quenching. The 80-K magnetic moment is found to decrease from 2.4μ_B in CrTe to 1.52μ_B in Cr_0.6V_0.4Te. The Curie temperature varies from 342 K to 321 K, respectively.     

Thermal conductivity of Er<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Se (<Emphasis Type="Italic">x</Emphasis> ≤ 0.025) solid solutions

The thermal conductivity of Er _x Sn_{1 ? x} Se solid solutions has been measured at temperatures from 80 to 360 K. The results have been used to evaluate the electronic and lattice components of thermal conductivity for elastic carrier scattering, parabolic bands, and arbitrary degeneracy. With increasing erbium content and temperature, both the electronic and lattice components decrease considerably. Long-term annealing increases both components. It follows from the present experimental data that heat conduction in Er _x Sn_{1 ? x} Se is mainly due to phonons and that the observed rise in thermal resistance with Er content is due to phonon-phonon and paramagnetic-ion scattering.     

Energy spectrum of charge carriers in Sm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te

The electrical conductivity (σ), Hall coefficient (R _H, and thermopower (α) of Sm _x Pb_{1 − x} Te have been measured at temperatures from 80 to 800 K. The results demonstrate that the Sm _x Pb_{1 − x} Te solid solutions with x ≤ 0.04 are p-type semiconductors. We have determined the electron effective mass at the conduction band bottom (m _n = (0.031 ± 0.001)m ₀) and Fermi level (m* = (0.06 ± 0.001)m ₀) and the hole effective mass (m _p = (0.34 ± 0.001)m ₀). The temperature-dependent σ, R _H, and α data are interpreted in terms of a model with two carrier types.     

Enhanced Superconductivity in Double-Doping Cu<Subscript>0.15</Subscript>TaSe<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript><Emphasis Type="Italic">S</Emphasis><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Superconducting Cu _x TaSe₂(x=0.05, 0.15) and Cu_0.15TaSe_2?x S _x (x=0, 0.5, 1, 1.5) single crystals have been systematically fabricated by a chemical vapor transport method. It is found that the double doping in TaSe₂, i.e., the simultaneous intercalation of Cu and substitution of Se by S, can substantially enhance the superconducting transition temperature. Transport property measurements give evidence of the coexistence and competition of charge density wave state and superconductivity in Cu _x TaSe₂ which provide meaningful information to understand the complex electronic states in this system. The parallel shift and the fan-shape broadening behaviors are observed in the superconducting transition curves under magnetic fields of Cu_0.15TaSeS and TaSeS, respectively, indicating an increase of coherence length and suppression of superconducting fluctuation induced by copper intercalation.     

Relaxation phenomena in EDAMn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cl<Subscript>4</Subscript> perovskite; 0≤ <Emphasis Type="Italic">x</Emphasis> ≤ 1 perovskite

The electrical properties measurements were carried out for the complex (CH₂)₂Mn_1–xCd_xCl₄, 0.0 x 1.0 at different temperatures as a function of frequency (100–1000 kHz). Four transition points were obtained for x = 0.5, which were assigned as thermochroism, interlayer exchange interaction, order-disorder and chain melting transition. The presence of more than one straight line in the conductivity data clarifies the presence of more than one conduction mechanism, and the calculated values of the activation energy indicate the semiconducting characteristics of the investigated complexes. The values of the relaxation time depend on Cd-content as well as the heating temperature. The expected critical concentration at x = 0.5 agrees well with the percolation theory of Mont-Carlo group. The IR spectra indicate that, the force constant of the bonds and the atomic mass vibration are affected by Cd-content.     

Thermal conductivity of Sn<Subscript>1–<Emphasis Type="Italic">x</Emphasis> </Subscript>Mn<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>Te single crystals

The thermal conductivity of homogeneous crystalline Sn_1–xMn_xTe samples has been measured in the temperature range 90–305 K. We have determined their electron and lattice thermal conductivities and their thermal resistivity due to structural defects. The results demonstrate that the electron thermal conductivity reaches ~50% of the total thermal conductivity in some of the samples and that structural defects make an appreciable contribution to the thermal resistivity of the crystals.     

Synthesis of ultrafine fluorite Sr<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Nd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>F<Subscript>2 + <Emphasis Type="Italic">x</Emphasis></Subscript> powders

We have identified conditions that ensure the preparation of ultrafine Sr_{1 − x} Nd _x F_{2 + x} powders uniform in phase composition. The powders were characterized by X-ray diffraction and scanning electron microscopy. The powder particles have the form of faceted nano- and microcubes and range in size from 30–100 nm to 0.3–2.5 μm, depending on precipitation conditions.     

Mechanism of nanostructuring in fluorite-like Ca<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>F<Subscript>2 + <Emphasis Type="Italic">x</Emphasis></Subscript>

Nanostructuring in fluorite-like Ca_{1 ? x} La _x F_{2 + x} is shown to be associated with the precipitation of an CuAu-ordered phase. The shape of the precipitates is governed by the energetics of the {001} and {111} faces of tetragonal inclusions in highly anisotropic media and is nearly cuboctahedral. The misfit strain relaxes through the generation of twins, which nucleate along the intersection lines of {001} and {111} faces. The twins impede facial development and further growth and ordering of precipitates, thereby freezing the precipitation process in its initial stage. For this reason, the phase segregation is difficult to reveal, and Ca_{1 ? x} La _x F_{2 + x} crystals appear homogeneous.     

Homogeneity of high-resistivity <Emphasis Type="Italic">p</Emphasis>-Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>〈Au〉 crystals

p-Si_{1 ? x} Ge _x crystals have been diffusion-doped with gold. Gold diffusion in the p-Si_{1 ? x} Ge _x 〈Au〉 samples and their electrical properties have been studied. The results demonstrate that the highest gold concentration in the crystals can be achieved in the temperature range 1000–1050°C. An expression has been derived which indicates that, all other factors being the same, compensation with Au, an amphoteric impurity, insures better homogeneity compared to codoping with acceptor and donor impurities. The hole concentration homogeneity in gold-compensated samples is at the same level as or even better than that in the uncompensated material.     

Electronic and magnetic properties of semimagnetic semiconductors Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te

The electronic and the magnetic of semimagnetic semiconductors Hg_1−x Mn _x Te are studied. The magnetic phase diagrams have been determined by the replica method in the framework of the XY model using variational principle. A spin glass state has been obtained for x<x _c (x _c≈0.6). This phase is attributed to the randomness and the frustration of the antiferromagnetic interactions between the Mn magnetic ions arising from the topology of semimagnetic semiconductors Hg_1−x Mn _x Te. The sp³ semiempirical nearest-neighbor tight-binding formalism is used to compute the band structures of the above two systems in the hole range of concentration 0≤x≤1. The variation of the gap energy E _g with x is plotted.     

Magnetic Behaviors of Ferromagnetic Semiconductor Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te Grown by MBE

The magnetic and structural properties of MBE-grown films of Zn_1?xCr _x Te were investigated. The magnetization versus magnetic field (M–H) measurement of Zn_1?xCr _x Te (x = 0.01–0.17) showed clear hysteresis loop at low temperatures. The ferromagnetic transition temperature (T_C) estimated from the Arrott-plot analysis increased almost linearly with the Cr composition (x) up to 275 K at x = 0.17. However, in the magnetization versus temperature (M–T) measurement, the irreversibility between the zero-field-cooled (ZFC) and field-cooled (FC) processes was observed. This is typically observed in the magnetic random system such as spin-glass or superparamagnetic phase. In the high resolution transmission microscopy (HRTEM) observations, structural defects such as stacking faults and polycrystalline-like structure were observed at high Cr compositions, whereas any apparent precipitates of different phases were not seen in all the range of Cr compositions examined. The correlation of the observed magnetic randomness with the local structural defects was discussed.     

Raman spectroscopy determination of carrier concentration in <Emphasis Type="Italic">n</Emphasis>-In<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>As epitaxial films

We have studied in detail the coupled phonon-plasmon mode Raman spectra of n-In _x Ga_{1 − x} As with n in the range 10¹⁷ to 10¹⁹ cm⁻³. The results indicate that the behavior of the high-frequency mode L ₊ can be described in terms of coupled modes in the Drude approximation. The proposed theory and experimental data are used to estimate the carrier concentration in the solid solution and its composition.