Electron spin resonance in Cd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>x</Subscript>Te and Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>x</Subscript>Te compounds

Electron spin resonance in semimagnetic Cd_1?xMn_xTe (0<x<0.7) and Zn_1?xMn_xTe (0<x<0.53) compounds was studied at temperatures of 77 and 300 K. It is found that two types of paramagnetic centers exist in Zn_1?xMn_xTe, one of which is related to Mn²⁺ ions and the other is attributed to structural defects in the crystals.     

Optical and thermal properties of CuAl<Subscript>x</Subscript>In<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>2</Subscript> solid solutions

The optical and thermal properties of crystals of CuAl_xIn_1?xTe₂ solid solutions grown by the Bridgman-Stockbarger method were studied for the first time. From the transmission and reflection spectra in the region of the intrinsic-absorption edge, the band gap (E _g ) was determined for the CuInTe₂ and CuAlTe₂ compounds and for their solid solutions; the concentration dependence of E _g was plotted. The E _g value was found to vary nonlinearly with x and can be described by the quadratic dependence. Dilatometry was used to study the thermal expansion of these solid solutions. The coefficient of thermal expansion (α_L) was shown to have a λ-shaped temperature dependence in the region of phase transitions. The isotherms are plotted for the concentration dependence of α_L. The thermal conductivity was investigated and its concentration dependence was plotted. The dependence of the thermal conductivity on x was established to have a minimum in the region of medium compositions.     

Photoelectric properties of surface-barrier structures based on Zn<Subscript>2−2<Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>x</Subscript>In<Subscript>x</Subscript>Se<Subscript>2</Subscript> films obtained by selenization

p-Zn_2?2xCu_xIn_xSe₂ (ZCIS) polycrystalline films 1–2 ¼m thick have been obtained by selenization. Photosensitive surface-barrier In/p-ZCIS structures are fabricated based on the films. The spectra of relative quantum efficiency of the structures obtained by selenization of the initial ZnSe/(Cu-In) and (Zn-Cu-In) films are examined. The optical band gap of the Zn_2?2xCu_xIn_xSe₂ films is determined. Conclusions are reached on the prospects for the use of the obtained films as broadband photoconverters of natural optical radiation.     

Specific features of conductivity of Cd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>x</Subscript>Te and Cd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>x</Subscript>Te single crystals

The electrical characteristics of p-type Cd_1?xZn_xTe (x=0.05) and Cd_1?xMn_xTe (x=0.04) single crystals with a resistivity of 10³–10¹⁰ Ω cm at 300 K are studied. The conductivity and its variation with temperature are interpreted on the basis of statistics of electrons and holes in a semiconductor with deep acceptor impurities (defects), with regard to their compensation by donors. The depth of acceptor levels and the degree of their compensation are determined. The problems of attaining near intrinsic conductivity close to intrinsic are discussed.     

Electronic and vibrational states in InN and In<Subscript>x</Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N solid solutions

The review presents the results of optical studies of the fundamental physical characteristics of InN, the material which remains the least studied among nitrides of Group-III elements. The results of early optical studies of InN are analyzed and compared with recent data. New experimental facts reported in the review refer to hexagonal single-crystal epitaxial InN layers with an electron concentration of (1?2)×10¹⁸ to 6×10²⁰ cm^?3, which are grown by molecular beam epitaxy (MBE) and metal-organic vapor-phase epitaxy (MOVPE) on Al₂O₃ substrates. The aim of this review is to make a joint analysis of optical spectra (absorption, photoluminescence (PL), PL excitation, and photomodulated reflection) near the fundamental band gap. Furthermore, basic structural and electrical characteristics that have been obtained by a whole range of techniques are given for epitaxial layers of hexagonal InN. The principal result of recent studies is that the hexagonal InN crystal is a narrow-gap semiconductor with a band gap of 0.65–0.7 eV. Previously, the band gap of this material was considered to be 1.89 eV. It is shown that the Burstein-Moss effect accounts for the strong difference between the band gap and the optical absorption threshold in InN samples with a high concentration of electrons. The small value of the band gap of hexagonal InN is confirmed by optical studies of In_xGa_1?xN solid solutions at high concentrations of In. Theoretical calculations of the band structure of hexagonal InN crystals are briefly reviewed.     

Tunable Coplanar Waveguide Phase Shifter Using Ba<Subscript>x</Subscript>Sr<Subscript>1−x</Subscript>TiO<Subscript>3</Subscript> Thin Films on LaAlO<Subscript>3</Subscript> Substrates

A kind of distributed coplanar waveguide (CPW) phase shifter based on LaAlO₃ substrates is designed and fabricated in this paper. The Ba_0.4Sr_0.6TiO₃ (BST) thin films employed in the circuits are deposited by RF magnetron sputtering, and then annealed at 800°C for 30 min in air. The dielectric tunability, loss tangent of the BST films are respectively 43.7% and 0.017 at 100 kHz and 30 V, the leakage current is approximately 1 × 10⁻⁹A/cm² at zero bias voltage. The CPW phase-shifter designed is subsequently fabricated in order to obtain a 360° phase shift at 30 GHz with a moderate bias voltage. The maximal phase shift is 372° at 22.5 GHz with a bias voltage of 40 V.     

Thermoelectric Properties and Electronic Structure of Bi- and Ag-Doped Mg<Subscript>2</Subscript>Si<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Compounds

Mg₂Si_1−x Ge _x compounds were prepared from pure elements by melting in tantalum crucibles. The reaction was conducted under an inert gas in a special laboratory setup. Samples for thermoelectric measurements were formed by hot pressing. Structure and phase composition of the obtained materials were investigated by x-ray diffraction (XRD). Morphology and chemical composition were examined by scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS), respectively. Thermoelectric properties, i.e., the Seebeck coefficient, the electrical conductivity, and the thermal conductivity, were measured in the temperature range of 500 K to 900 K. The effect of Bi and Ag doping on the thermoelectric performance of Mg-Si-Ge ternary compounds was investigated. The electronic structures of binary compounds were calculated using the Korringa–Kohn–Rostoker (KKR) method. The effects of disorder, including Ge substitution and Bi or Ag doping, were accounted for in the KKR method with coherent potential approximation calculations. The thermoelectric properties of doped Mg₂Si_1−x Ge _x are discussed with reference to computed density of states as well as the complex energy band structure.     

Galvanomagnetic effects in atomic-disordered HgSe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>x</Subscript> compounds

In HgSe and HgSe_1?xS_x single crystals irradiated with electrons of 5 MeV energy at 270 K, resistivity and the Hall effect have been studied in the temperature range 1.7–370 K in magnetic field up to 13.6 T. Changes in the carrier density and mobility upon generation of radiation-induced defects and subsequent isochronous annealings have been determined. The irradiation made it possible to reduce the electron density to a greater extent than do conventional methods, as well as to restore the initial value by annealing.     

A ferroelectric field effect transistor based on a Pb(Zr<Subscript>x</Subscript>Ti<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>)O<Subscript>3</Subscript>/SnO<Subscript>2</Subscript> heterostructure

The possibility of fabricating a ferroelectric FET based on a Pb(Zr_xTi_1?x)O₃/SnO₂ (PZT/SnO₂) heterostructure is investigated. Sb-doped epitaxial SnO₂/Al₂O₃ thin film deposited by YAG laser ablation from a metal target is used as the FET channel. The highest obtained electron mobility in the channel is 25 cm²/(V s) at an electron density of 8 × 10¹⁹ cm^?3. The possibility of growing PZT film directly on SnO₂ film using two different techniques, laser ablation and magnetron sputtering, is demonstrated. Both methods have been used in the fabrication of Au/PZT/SnO₂ capacitor heterostructures, whose top Au electrode is 250×250 μm² in size. These cells demonstrate a capacitance of 1000 pF at a 10-V bias and remnant polarization up to 16 μC/cm². A Au/PZT/SnO₂/Al₂O₃ transistor structure with 94% modulation of the channel current is fabricated. The difference in the channel current under the effect of positive and negative remnant polarization of the undergate ferroelectric is 37%.     

Electronic and optical properties of AlAs/Al<Subscript>x</Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>As(110) superlattices

Electronic states in the conduction band of (AlAs)_M(Al_xGa_1?xAs)_N(110) superlattices are investigated for various M and N. It is shown that electronic properties of these structures are mainly determined by electrons of two pairs of valleys, namely, either Γ-X ^Z or X ^X –X ^Y . Calculations based on the developed model of joining the envelope functions were carried out. Miniband spectra, symmetry, and localization of wave functions, as well as probabilities of miniband-to-miniband infrared absorption, are determined and analyzed. It is shown that, in the case of the X ^X –X ^Y pair of valleys, the absorption probabilities are high not only for polarization of light along the growth axis of the superlattice but also for the normal incidence of an optical wave on the structure surface.     

Alternating current conductivity and electron spin resonance of the Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>x</Subscript>Te alloys

The results of measurements of frequency dependences of conductivity and electron spin resonance (ESR) of the Cd_{1 ? x} Fe_xTe alloys (0.01 ≤ x ≤ 0.05) at room temperature are presented. It is found that, in the composition range 0.003 ≤ x ≤ 0.05, a new asymmetric ESR absorption line with g ≈ 3.9 emerges, and its hysteresis manifests itself while the samples are magnetized. The line with g ≈ 3.9 is attributed to the charge state 3⁺ of the Fe atoms, which occurs in tetrahedra with three Fe atoms.     

Electronic and structural transitions in Pb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>x</Subscript>Te:Ga alloys under pressure

The effect of pressure on electrical properties of Ga-doped n-Pb_1?xGe_xTe 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.     

(IV<Subscript>2</Subscript>)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(III-V)<Subscript>x</Subscript> solid solutions obtained from a bounded tin melt-solution

The formation of a continuous series of substitutional solid solutions is theoretically considered from the viewpoint of taking into account generalized moments and differences in the valence and the covalent radii of atoms or molecules of initial components. These considerations are used to develop technology for the fabrication of (Si₂)_1?x(GaAs)_x (0≤x≤0.96) and (Si₂)_1?x(GaP)_x (0≤x≤1) epitaxial layers on silicon substrates from a tin melt-solution by the forced cooling method. The distribution of components over the thickness of the (Si₂)_1?x(GaAs)_x and (Si₂)_1?x(GaP)_x layers, the photosensitivity, and the current-voltage characteristics of Si-(Si₂)_1?x(GaAs)_x and Si-(Si₂)_1?x(GaP)_x heterostructures were studied. The analysis of results of X-ray investigations and photoelectric properties indicate that the grown epitaxial layers of (IV₂)_1?x(III-V)_x solid solutions are structurally perfect.     

Synthesis and Transport Properties of In<Subscript>4</Subscript>(Se<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>3</Subscript>

Polycrystalline samples of In₄(Se_1−x Te _x )₃ were synthesized by using a melting–quenching–annealing process. The thermoelectric performance of the samples was evaluated by measuring the transport properties from 290 K to 650 K after sintering using the spark plasma sintering (SPS) technique. The results indicate that Te substitution can effectively reduce the thermal conductivity while maintaining good electrical transport properties. In₄Te₃ shows the lowest thermal conductivity of all compositions tested.     

Modification of Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript>x</Subscript>Te properties by low-energy ions

We present an overview concerning the modification of properties of HgCdTe solid solutions and related Hg-containing materials under surface treatment with low-energy (60–2000 eV) ion beams. The conditions for conductivity-type conversion in p-material, dose, and time dependences of the depth of the conversion layer are analyzed. The modification of electrical properties of n-type material subjected to ion-beam treatment is discussed. The suggested mechanisms of conductivity-type conversion under low-energy ion treatment of HgCdTe doped with vacancies or acceptor impurities are regarded. Properties of p-n junctions produced by this technique are reviewed, and electrical and photoelectric parameters of HgCdTe IR photodetectors fabricated by low-energy ion treatment are analyzed. Several examples of novel device structures developed with the use of the method are presented.     

Effective electron mass in a Mn<Subscript>x</Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te system

The reflection spectra of n-Mn_xHg_1?xTe single crystals and epitaxial layers were measured at 300 K. The effective electron mass was determined for the samples with x=0.06–0.10 and an electron concentration N>6×10¹⁶ cm^?3. The calculated values of effective electron mass are close to experimental values.     

Optical properties of AgGa<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>In<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>2</Subscript> alloys

Coarse-grained crystals of AgGaSe₂ and AgInSe₂ ternary compounds and their alloys are grown by planar crystallization of the melts. For the crystals produced in this way, the transmittance spectra near the fundamental absorption edge are studied. From the experimental spectra, the band gap (E _g) and its variation with composition are determined. It is established that E _g is a nonlinear function of the composition parameter x. The dependence E _g (x) is calculated theoretically in the context of the Van Vechten-Bergstresser model and Hill-Richardson pseudopotential model.     

Study of the electrical properties of Cd<Subscript>x</Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te

On the basis of the temperature and field dependences of the Hall coefficient R _H , it was found that samples with a low electron density are, as a rule, compensated, and the degree of compensation changes upon thermal conversion of the conductivity of the sample to p type. For n-Cd_xHg_1?xTe, the ionization energy of the donor level was found from the temperature dependences of resistivity ρ(T): E _d =24–32 meV. For the same samples, after their thermal conversion to p type, the ionization energies of acceptors, which are related to doubly charged vacancies V _Hg ⁺⁺ , were determined: E _a =32 and 48 meV. In addition, a deep level E _t , related to an unknown amphoteric impurity, was found (E _t ?E _v ≈0.7E _g ).     

Structure and Thermoelectric Properties of Te- and Ge-Doped Skutterudites CoSb<Subscript>2.875−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>0.125</Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

n-Type CoSb_2.875−x Ge_0.125Te _x (x = 0.125 to 0.275) compounds with different Te contents have been synthesized by a melt–quench–anneal–spark plasma sintering method, and the effects of Te content on the structure and thermoelectric properties have been investigated. The results show that all specimens exhibited n-type conduction characteristics. The solubility limit of Te in CoSb_2.875−x Ge_0.125Te _x is found to be x = 0.25. The solubility of Te in CoSb₃ is increased through charge compensation of the element Ge. The room-temperature carrier concentration N _p of CoSb_2.875−x Ge_0.125Te _x skutterudites increases with increasing Te content, and the compounds possess high power factors. The maximum power factor of 3.89 × 10⁻³ W m⁻¹ K⁻² was obtained at 720 K for the CoSb_2.625Ge_0.125Te_0.25 compound. The thermal conductivity decreases dramatically with increasing Te content due to strong point defect scattering. The maximum value of the thermoelectric figure of merit ZT = 1.03 was obtained at 800 K for CoSb_2.625Ge_0.125Te_0.25, benefiting from a lower thermal conductivity and a higher power factor. The figure of merit is competitive with values reported for single-filled skutterudites.     

The Power Factor of Bi<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Tl<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>3</Subscript> Single Crystals

Single crystals of the ternary system Bi_2−x Tl _x Se₃ (nominally x = 0.0 to 0.1) were prepared using the Bridgman technique. Samples with varying content of Tl were characterized by measurement of lattice parameters, electrical conductivity σ _⊥c, Hall coefficient R _H(B║c), and Seebeck coefficient S(ΔT⊥c). The measurements indicate that incorporation of Tl into Bi₂Se₃ lowers the concentration of free electrons and enhances their mobility. This effect is explained within the framework of the point defects in the crystal lattice, with formation of substitutional defects of thallium in place of bismuth (Tl_Bi) and a decrease in the concentration of selenium vacancies (V_Se ^{+ 2} V_{\rm{Se}}^{ + 2} ). The temperature dependence of the power factor σS ² of the samples is also discussed. As a consequence of the thallium doping we observe a significant increase of the power factor compared with the parent Bi₂Se₃.