Quaternary (FeIn2S4)x(MnIn2S4)1 ? x alloys and photosensitive structures on their basis

Using directional crystallization of the melt of the (FeIn₂S₄) _x (MnIn₂S₄)_{1 − x} alloy, homogeneous crystals of a similar atomic composition are grown over the entire range of compositions 1 ≥ x ≥ 0. It is established that the crystals of the continuous series of quaternary alloys in the range x = 0–1 crystallize in the spinel structure and lattice parameter a linearly depends on x. It is established that it is possible to obtain In(Al)/(FeIn₂S₄) _x (MnIn₂S₄)_1–x photosensitive structures. Room-temperature spectra of relative quantum efficiency of photoconversion of the In(Al)/(FeIn₂S₄) _x (MnIn₂S₄)_{1 − x} structures fabricated for the first time are obtained. From the analysis of these spectra, activation energies of direct and indirect band-to-band transitions for the crystals of the (FeIn₂S₄) _x (MnIn₂S₄)_1–x alloys are determined and the dependence of these parameters on the composition of the position-disordered phases of mentioned alloys is discussed. It is concluded that the crystals of the (FeIn₂S₄) _x (MnIn₂S₄)_{1 − x} alloys can be used in broadband photoconverters of optical radiation.     

Thermoelectric Properties of Tix(HfyZr1?y)1?xNiSn0.998Sb0.002 Half-Heusler Ribbons

Ribbons of Ti _x (Hf _y Zr_1−y )_1−x NiSn_1−z Sb _z (x = 0.1 to 1, y = 0.1 to 0.9, z = 0, 0.002, 0.004) were prepared by spin casting and annealed for 1 h at T _a = 1000 K, 1050 K, 1073 K, and 1100 K. The crystal phase of the ribbons was investigated by x-ray diffraction analysis and transmission electron microscopy. All the ribbons consisted of a phase with a half-Heusler structure. The Seebeck coefficient, electrical conductivity, thermal conductivity, power factor, and figure of merit ZT at room temperature were clarified experimentally as a function of x, y, z, and T _a. Despite the large thermal conductivity, the power factor and figure of merit were remarkably large at x = 0.5, y = 0.5, z = 0.002, and T _a = 1073 K, because the Seebeck coefficient and electrical conductivity were large.     

Properties and structure of (As2Se3)1 ? z (SnSe2) z ? x (Tl2Se) x and (As2Se3)1 ? z (SnSe) z ? x (Tl2Se) x glasses

Tin is stabilized in the bivalent and tetravalent states in the structure of (As₂Se₃)_{1 − z} (SnSe₂) _{z − x} (Tl₂Se) _x and (As₂Se₃)_{1 − z} (SnSe) _{z − x} (Tl₂Se) _x glasses. The presence of bivalent tin in the structural network of a glass does not give rise to extrinsic conductivity. Dependences of density, microhardness, and the glass-transition temperature on the composition of the glasses are interpreted using a model according to which the structure of the glasses is composed of structural units that correspond to As₂Se₃, AsSe, TlAsSe₂, Tl₂Se, SnSe, and SnSe₂ compounds. Original Russian Text ? G.A. Bordovsky, A.V. Marchenko, E I. Terukov, P.P. Seregin, T.V. Likhodeeva, 2008, published in Fizika i Tekhnika Poluprovodnikov, 2008, Vol. 42, No. 11, pp. 1353–1356.     

Discovery of the (In2S3)x(MnIn2S4)1 ? x solid solutions and fabrication of photosensitive structures based on them

A technology of growing single crystals of (In₂S₃) _x (MnIn₂S₄)_{1 − x} solid solutions that provides control over their atomic composition in the entire concentration range 0 ≤ x ≤ 1 is developed. It is shown that, in the range x = 0–1, the single crystals have the cubic spinel structure and the unit cell parameter a follows the linear dependence on x. The exponential character of the temperature dependence of resistivity of solid solutions, on which the first photosensitive Cu/(In₂S₃)x(MnIn₂S₄)_{1 − x} structures are obtained, is revealed. The first photosensitivity spectra of these structures are obtained, and, based on these spectra, dependences of energy of the direct and indirect band-to-band transitions on the composition x are determined. The possibility of applying these structures in broad-band photoconverters of optical radiation is concluded.     

Growth of the (In2S3)x(FeIn2S4)1 ? x single crystals and properties of photoelectric structures on their basis

Complete mutual solubility in the (In₂S₃) _x (FeIn₂S₄)_{1 − x} system is established. The technology is developed, and single crystals of the continuous series of the (In₂S₃) _x (FeIn₂S₄)_{1 − x} solid solutions are grown for the first time. The linear dependence of the unit cell parameter of single crystals with a cubic spinel lattice on the solid solution composition is found. First, photosensitive Schottky barriers are fabricated, and then, based on studies of their photosensitivity, the character of band-to-band transition is discussed and the values of the band gap depending on the atomic composition are estimated. The possibility of using the obtained solid solutions as broadband photoconverters of optical radiation is revealed.     

Thermoelectric Properties of Ag-Doped n-Type (Bi2?xAgxTe3)0.96?(Bi2Se3)0.04 Pseudobinary Alloys

n-Type thermoelectric powders of (Bi_2−x Ag _x Te₃)_0.96−(Bi₂Se₃)_0.04 (0 ≤ x ≤ 0.05) have been synthesized by mechanical alloying and then consolidated by spark plasma sintering. The analysis results show that the grain size of pure Bi, Te, Ag, and Se powders is decreased to about 1 μm to 0.5 μm after they are mechanically alloyed for 2 h. The power factor of bulk material increases with increasing Ag-doping content, while the trend for the lattice thermal conductivity is the opposite. Bulk (Bi_0.99Ag_0.04)₂(Te_0.96Se_0.04)₃ after milling for 12 h exhibits a higher power factor, lower thermal conductivity, and thus a higher ZT of 0.74 at 373 K.     

Pulsed Electroplating: a Derivate Form of Electrodeposition for Improvement of (Bi1?xSbx)2Te3 Thin Films

Bismuth antimony telluride (Bi_1−x Sb _x )₂Te₃ thermoelectric compounds were synthesized by pulse plating. Due to the large number of parameters available (pulse waveform, on/off pulse time, applied current density), this advanced form of electrodeposition allows better control of the interfacial supply and electrochemical reactions and offers effective ways to improve macroscopic properties such as adhesion and to produce crack-free hard deposits and fine-grained films with higher uniformity and lower porosity. The influence of pulse parameters (pulse time t _on, cathodic current density J _c) on the stoichiometry, roughness, and crystallography of deposits was studied. The thermoelectric properties (electrical resistivity and Seebeck coefficient) of the films were measured. The results revealed that deposits have p-type conductivity directly after electroplating (Seebeck coefficient around 150 μV K⁻¹), in contrast to films synthesized by direct current, which require annealing. An improvement of resistivity was observed: for a direct-current-deposited film the resistivity is around 5000 μΩ m, whereas for a pulse-deposited film the resistivity was around 200 μΩ m.     

Pb(Zn1/3Nb2/3)0.2(Hf1-xTix)0.8O3陶瓷压电能量收集特性研究

采用铌铁矿前驱体两步法制备了Pb(Zn_1/3Nb_2/3)_0.2(Hf_1-xTi_x)_0.8O₃(PZNH_1-xT_x)钙钛矿压电陶瓷,研究了铪钛比对陶瓷相结构、电学性能和能量收集特性的影响。结果表明,当x=0.52时,陶瓷样品位于准同型相界,具有最优综合压电性能：居里温度T_C=287 ℃,品质因数FOM≈14 753×10^-15 m²/N,压电电荷常数d₃₃=492 pC/N。由该组成材料构建的悬臂梁型压电能量收集器输出功率密度高达4.16 μW/mm³,所转化的电能可成功点亮138盏并联的LED灯。结果表明,PZNHT陶瓷在压电能量收集领域具有良好的应用潜力。     

Chemical–Mechanical Polishing of CdTe and ZnxCd1?xTe Single Crystals by H2O2(HNO3)–HBr–Organic Solvent Etchant Compositions

Chemical–mechanical polishing of CdTe and Zn _x Cd_1−x Te single-crystal surfaces by bromine-evolving compositions based on aqueous solutions of H₂O₂(HNO₃)–HBr–solvent has been investigated. The dependences of the chemical–mechanical polishing rate on the dilution of the base polishing etchant for various organic components have been determined. The surface condition after such polishing has been investigated using profilometry. The polishing etchant compositions for CdTe and Zn _x Cd_1−x Te single-crystal surfaces and the chemical polishing conditions have been optimized.     

Single-Crystal Investigations on Quaternary Clathrates Ba8Cu5SixGe41?x (x?=?6, 18, 41)

Type I clathrates have been considered as promising thermoelectric materials due to their special structural characteristics: the “rattling” guest atoms in the larger of the two cages of the clathrate I structure are frequently held responsible for the low lattice thermal conductivity. By single-crystal x-ray diffraction, we investigated the quaternary clathrates Ba₈Cu₅Si _x Ge_41−x (x = 6, 18, 41). Rietveld refinements confirmed that the clathrates in this system crystallize with cubic primitive symmetry, in the type I clathrate structure, and that no phase transitions occur in the temperature range investigated (100 K to 300 K). We derive the concentration dependencies of the Debye temperature, the Einstein temperatures, the static disorder parameters, and the size of the two cages and argue that these dependencies underpin the previously assumed different bonding character of the Ba guest atoms in the larger and smaller cages. The linear thermal expansion coefficients for the samples are derived.     

Transport and Thermoelectric Properties of the Ca1?xSrxRu1?yMnyO3 System

The magnetic, transport, and thermoelectric properties of Ca_1−x Sr _x Ru_1−y Mn _y O₃ have been investigated. Ferromagnetism with relatively high T _C (>200 K) was introduced by Mn doping. In particular, ferromagnetism appeared in the Ca_0.5Sr_0.5Ru_1−y Mn _y O₃ system at y > 0.2. The maximum T _C (=270 K) was recorded for a specimen of Ca_0.5Sr_0.5Ru_0.4Mn_0.6O₃. The ferromagnetism seems to be due to the mixed-valence states of Mn³⁺, Mn⁴⁺, Ru⁴⁺, and Ru⁵⁺ ions. The metallic character of Ru-rich specimens was suppressed by Mn substitution, and the system was transformed into a semiconductor at relatively low Mn content near y = 0.1. Specimens with higher Mn content (y > 0.8) had large thermoelectric power (50 μV K⁻¹ to 130 μV K⁻¹ at 280 K) accompanied by relatively low resistivity (0.03 Ω cm to 1 Ω cm). The Ca_0.5Sr_0.5Ru_1−y Mn _y O₃ system seems to have good potential as a thermoelectric material for use above 300 K.     

Crystallophysical properties of the In1 ? yGayAs1 ? xNx/GaAs heterostructures

Some properties of the In_{1 − y} Ga _y As_{1 − x} N _x unordered alloys and physical prerequisites of their use in science and technology are considered. The results of studying the intermolecular interaction in the systems under study and the features of their application to the In_{1 − y} Ga _y As_{1 − x} N _x /GaAs functional hetero-structures are presented.     

Improved Thermoelectric Properties of (GeTe)90(AgySb2?yTe3?y)10 by Tuning the Ag-to-Sb Ratio

(GeTe)₉₀(Ag _y Sb_2−y Te_3−y )₁₀ (y = 0.6, 0.7, 0.8, 1.0) compounds were prepared by combining melting and hot pressing, and the thermoelectric properties were studied over the temperature range of 300 K to 770 K. Powder x-ray diffraction results revealed that all the samples were the rhombohedral phase with space group R3m. The electrical conductivity of samples decreased with temperature, while the Seebeck coefficient increased. The thermal conductivity of all the samples was very low, especially for those with the lower y values. High ZT values above 1.6 were obtained for the samples with y = 0.6, 0.7, and 0.8.     

Electronic and Optical Properties of MgxZn1?xO and BexZn1?xO Quantum Wells

As a preparatory step toward establishing reliable numerical design tools for ZnO-based optoelectronic devices, we have reassessed the available information on material parameters relevant for the simulation of light-emitting diodes (LEDs) with active regions including ZnO, MgZnO, and BeZnO layers. The impact of different approximations for the electronic structure and the interface polarization charge on the optical properties of bulk ZnO and ZnO/MgZnO quantum wells has been evaluated, and a consistent set of parameters has been used not only for systematic comparison of ZnO/MgZnO and ZnO/BeZnO single quantum well structures but also for the first simulation of a realistic ZnO/BeZnO multiple quantum well LED.     

Influence of Cadmium Composition on CH4–H2-Based Inductively Coupled Plasma Etching of Hg1?xCdxTe

In this paper, inductively coupled plasma etching of Hg_1−x Cd _x Te in CH₄–H₂-based chemistry is studied. This work is focused on the effects of substrate temperature, ion energy, and alloy composition on etch rate and surface composition. A strong influence of substrate temperature is shown. The etch rate is multiplied by more than a factor of 3 when the temperature is increased from 5°C to 35°C. A purely physical Cd removal mechanism is ruled out using x-ray photoelectron spectroscopy data from samples etched at different temperatures. Under the conditions of very low ion energy, an etching mechanism limited by the supply of active species from the plasma predicts an Hg_1−x Cd _x Te etch rate evolution that fits very well with our data.     

Optical properties of quaternary GaNxAsyP1 ? x ? y semiconductor alloys

The optical properties of quaternary GaN _x As _y P_{1 − x − y} semiconductor alloys grown on a GaP (100) substrate surface are studied by photoluminescence spectroscopy in the temperature range 20–300 K and by photoluminescence excitation spectroscopy at liquid-nitrogen temperature. The measurements are carried out for the GaN _x As _y P_{1 − x − y} alloys, for which the nitrogen and arsenic molar fractions x and y range from 0.006 to 0.012 and from 0.00 to 0.18, respectively. A comparative analysis of the data is conducted, and the dependences of the energy position of the photoluminescence peak on the composition of the quaternary alloy are established. From the studies of photoluminescence in the range 20–300 K, it is found that the temperature dependence of the position of the photoluminescence peak substantially differs from the behavior described by Varshni’s expression.     

I–V characteristic of p-n structures based on a continuous solid solutions (Si2)1 ? xx(CdS)x

The I–V characteristics of the p-Si-n-(Si₂) _{1 − x} (CdS) _x (0 ≤ x ≤ 0.01) structures are investigated at various temperatures. It is found that the I–V characteristic of such structures has a sublinear portion of the current growth with voltage V ≈ V ₀exp(JaW). The experimental results can be explained on the basis of the theory of the injection depletion effect. It is shown that the mobility of the minority carrier (hole) decreases with an increasing temperature. Original Russian Text ? A.S. Saidov, A.Yu. Leyderman, Sh.N. Usmonov, K.T. Kholikov, 2009, published in Fizika i Tekhnika Poluprovodnikov, 2009, Vol. 43, No. 4, pp. 436–438.     

Electrical and Thermal Properties of the Ca3?xGdxCo4O9+δ System

The effects of Gd substitution on the thermoelectric (TE) properties of Ca₃Co₄O_9+δ have been systematically investigated from 25 K to 335 K. Partial substitution of Gd in Ca₃Co₄O_9+δ results in an increase of thermopower and resistivity, and a decrease of thermal conductivity. A maximum dimensionless figure of merit (ZT) of 0.028 was achieved at 335 K for Ca_2.4Gd_0.6Co₄O_9+δ , which is about one order of magnitude larger than that for Ca₃Co₄O_9+δ . The investigation demonstrates that the TE performance of the Ca₃Co₄O_9+δ system can be improved through Gd doping.     

Optical properties of quantum-confined heterostructures based on GaPxNyAs1 ? x ? y alloys

The results of calculations of the band gap in GaP _x N _y As_{1 − x − y} alloys and the estimated parameter of hybridization of the conduction band in GaP and the localized level of nitrogen are reported. The optical properties of quantum-confined heterostructures based on GaP _x N _y As_{1 − x − y} alloys synthesized on the GaP (100) substrate surface are studied by photoluminescence measurements in the temperature range of 15–300 K. The heterostructures consist of GaP_0.814N_0.006As_0.18 quantum wells separated by GaP barrier layers. The well width and the barrier thickness are 5 nm. Heterostructures with different numbers of periods are considered. On optical excitation of the structures, an intense photoluminescence line is observed in the spectral range 620–650 nm. The photoluminescence spectra of the GaP_0.814N_0.006As_0.18/GaP quantum wells are profoundly broadened because of the inhomogeneity of the quaternary alloy in composition. It is established that the increase in the number of quantum well layers from 10 to 25 does not results in degradation of the photoluminescence properties of the heterostructures. The results of the study support the view that it is possible to produce efficient optoelectronic devices on the basis of GaP _x N _y As_{1 − x − y} alloys.     

Spinodal Decomposition of GaxIn1?xAsyP1?yQuaternary Alloys

Using X-ray structural analysis, scanning electron microscopy, atomic force microscopy, and photoluminescent spectroscopy, it is shown that it is possible to obtain a small-scale domain structure on the surface of liquid-phase epitaxial heterostructures. The domain structure emerges as a result of spinodal decomposition of the Ga _x In_{1 − x} As _y P_{1 − y} quaternary alloy due to immiscibility of its components and relaxation of its lattice parameter to surrounding layers.