Cathodoluminescence from dilute GaN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>As<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> solutions (<Emphasis Type="Italic">x</Emphasis> ≤ 0.03)

Cathodoluminescence from GaN _x As_1?x layers (0 ≤ x ≤ 0.03) was measured at photon energies ranging from the intrinsic absorption edge to 3 eV at room temperature. An additional emission band was visible in the visible range of the cathodoluminescence spectra. The intensity of this band is two orders of magnitude lower than the edge-emission intensity. The photon energy corresponding to the peak of this band and its FWHM are virtually independent of x and equal to ～2.1 and 0.6–0.7 eV, respectively. This emission is related to indirect optical transitions of electrons from the L _6c and Δ conduction-band minimums to the Γ₁₅ valence-band maximum.     

Optical properties of (CuInSe<Subscript>2</Subscript>)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>(2MnSe)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloys

The transmittance spectra of (CuInSe₂)_{1 − x} (2MnSe) _x alloy crystals grown by the Bridgman method are studied in the temperature range from 10 to 300 K. For these materials, the band gap and its temperature dependence are determined. It is shown that the band gap decreases with increasing temperature. The dependences of the band gap of the (CuInSe₂)_{1 − x} (2MnSe) _x alloys on the composition parameter x are plotted.     

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.     

Electrodeposition of Bi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sb<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Thermoelectric Films from DMSO Solution

The electrochemical behavior of nonaqueous dimethyl sulfoxide solutions of Bi^III, Te^IV, and Sb^III was investigated using cyclic voltammetry. On this basis, Bi _x Sb_2−x Te _y thermoelectric films were prepared by the potentiodynamic electrodeposition technique in nonaqueous dimethyl sulfoxide solution, and the composition, structure, morphology, and thermoelectric properties of the films were analyzed. Bi _x Sb_2−x Te _y thermoelectric films prepared under different potential ranges all possessed a smooth morphology. After annealing treatment at 200°C under N₂ protection for 4 h, all deposited films showed p-type semiconductor properties, and their resistances all decreased to 0.04 Ω to 0.05 Ω. The Bi_0.49Sb_1.53Te_2.98 thermoelectric film, which most closely approaches the stoichiometry of Bi_0.5Sb_1.5Te₃, possessed the highest Seebeck coefficient (85 μV/K) and can be obtained under potentials of −200 mV to −400 mV.     

Formation and optical properties of CuInSe<Subscript>2<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>2(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript> nanoparticles in a silicate glass matrix

Glasses containing nanoparticles of semiconductor CuInSe_2xTe_2(1?x) compounds (0≤x≤1) were fabricated by high-temperature melting of the mixtures of the glass-forming components and the corresponding compounds. Particles of average size 15–30 nm, whose characteristics were similar for compounds with different x, were formed. Optical absorption of the glasses near the fundamental absorption edge in the near-infrared and visible regions of the spectrum was studied, as well as the effect of additional heat treatment of glasses on their optical properties. The nature of the observed changes in the spectra with varying compound composition (the [Se]/[Te] ratio) was related to the possible transformations of the crystalline structure of nanoparticles.     

Pb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te Alloys: Application Considerations

The search for alternative energy sources is at the forefront of applied research. In this context, thermoelectricity, i.e., direct conversion of thermal into electrical energy, plays an important role, particularly for exploitation of waste heat. Materials for such applications should exhibit thermoelectric potential and mechanical stability. PbTe-based compounds include well-known n-type and p-type compounds for thermoelectric applications in the 50°C to 600°C temperature range. This paper is concerned with the mechanical and transport properties of p-type Pb_0.5Sn_0.5Te:Te and PbTe<Na> samples, both of which have a hole concentration of ∼1 × 10²⁰ cm⁻³. The ZT values of PbTe<Na> were found to be higher than those of Pb_0.5Sn_0.5Te:Te, and they exhibited a maximal value of 0.8 compared with 0.5 for Pb_0.5Sn_0.5Te:Te at 450°C. However, the microhardness value of 49 H_V found for Pb_0.5Sn_0.5Te:Te was closer to that of the mechanically stable n-type PbTe (30 H_V) than to that of PbTe<Na> (71 H_V). Thus, although lower ZT values were obtained, from a mechanical point of view Pb_0.5Sn_0.5Te:Te is preferable over PbTe<Na> for practical applications.     

Growth of (InSb)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>(Sn<Subscript>2</Subscript>)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films on GaAs substrates by liquid-phase epitaxy

The possibility of growing single-crystal substitutional (InSb)_{1 − x} (Sn₂) _x alloy (0 ≤ x ≤ 0.05) on the GaAs substrate by liquid-phase epitaxy from the In solution melt is established. The X-ray diffraction patterns and spectral and current-voltage characteristics of obtained n-GaAs-p-(InSb)_{1 − x} (Sn₂) _x heterostructures are studied at different temperatures. The lattice parameters of the (InSb)_{1 − x} (Sn₂) _x alloy are determined. It is found that the forward portion of the current-voltage characteristic of such structures at low voltages (up to 0.7 V) is described by the exponential dependence I = I ₀exp(qV/ckT), and at high voltages (V > 0.9 V), there is a portion of sublinear increase in the current with the voltage V ≈ V ₀exp(Jad). The experimental results are interpreted based on the injection depletion theory. It is shown that the product of mobility of majority carriers by the concentration of deep-level impurities increases as the temperature increases.     

Analysis of Dislocation Density in Pb<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se Grown on ZnTe/Si by MBE

The growth of (211) Pb_(1−x)Sn _x Se on Si is achieved with a thick ZnTe buffer layer. The obtained films are specular, but contain widely dispersed void defects. Because the lattice misfit between Pb_(1−x)Sn _x Se and ZnTe is small, dislocation density values on the order of 10⁶/cm² in the Pb_(1−x)Sn _x Se are obtained. The variation of the dislocation density as a function of Pb_(1−x)Sn _x Se thickness, h, is analyzed in terms of dislocation annihilation. The analysis predicts an inverse quadratic dependence of dislocation density on h, and quantitative agreement with experimental measurements of the dislocation density is obtained.     

Energy spectrum of charge carriers in TlIn<Subscript>1–<Emphasis Type="Italic">x</Emphasis> </Subscript>Yb<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>Te<Subscript>2</Subscript> solid solutions

The temperature dependences of the electrical conductivity σ(T), the Hall coefficient R(T), and the thermoelectric coefficient α(T) are investigated in TlIn_1–xYb_xTe₂ (0 < x < 0.10) solid solutions at 80–1000К. From the kinetic parameters, the effective masses of electrons and holes are determined. The obtained experimental data on σ(T) and α(T) are interpreted within the context of a model with one and two types of charge carriers. It is established that, since x = 0.05, the TlIn_1–xYb_xTe₂ solid solutions belong to the class of narrow-gap semiconductors that have high matrix elements of interaction.     

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.     

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.     

Investigation of the photoresistance of granular CdS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> films obtained by screen printing

Samples of CdS _x Se_{1 ? x} films were obtained by screen printing. It is shown that samples represent a granular composite with a high oxygen content (up to 20%). It is proved that transitions in the forbidden region of the CdS _x Se_{1 ? x} solid solution are responsible for light absorption changing the material resistance. The dependence of CdS _x Se_{1 ? x} samples resistance on illumination is studied. It is discovered that this type of materials has a photocurrent/dark current ratio higher than ten to the fifth power. The dependence of the conductivity on the sample structure is established.     

Pb<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te epitaxial films for terahertz detectors

Liquid-phase epitaxy is used to fabricate Pb_0.8Sn_0.2Te films, undoped or doped with indium to different levels. The depth profiles of the carrier density and dopant concentration in the films are measured and examined. A uniform dopant concentration to a depth of 15 μm is obtained. Electrical-conduction inversion is observed at a temperature of 77.3 K as the doping level is varied. The liquid-phase epitaxial method is shown to be a more suitable technology for the reproducible manufacture of epitaxial films with a given carrier density, such as the ones used in terahertz detectors.     

Radiative recombination channels in Si/Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanostructures

Using the solution of the 2D Schrödinger equation, systematic features of distribution of charge carriers in the Si/Si_{1 ? x} Ge _x nanostructures and variations in the efficiency of radiative recombination when pyramidal 2D clusters are transformed into 3D dome clusters with increasing thickness of nanolayers are established. The effect of the composition of the layers on the efficiency of the elastic stress in the structure and, as a consequence, the variation in conduction bands and valence band of the Si_{1 ? x} Ge _x nanostructures is taken into account. On realization of the suggested kinetics model, which describes recombination processes in crystalline structures, saturation of radiation intensity with increasing the pump intensity caused by an increase in the contribution of the Auger recombination is observed. A decrease in the contribution of the nonradiative Auger recombination is attained by decreasing the injection rate of carriers into the clusters, and more precisely, by an increase in the cluster concentration and an increase in the rate of radiative recombination.     

Investigation of MBE-Growth of Mid-Wave Infrared Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se

Undoped mid-wave infrared Hg_1?xCd_xSe epitaxial layers have been grown to a nominal thickness of 8–14 μm on GaSb (211)B substrates by molecular beam epitaxy (MBE) using constant beam equivalent pressure ratios. The effects of growth temperature from 70°C to 120°C on epilayer quality and its electronic parameters has been examined using x-ray diffraction (XRD) rocking curves, atomic force microscopy, Nomarski optical imaging, photoconductive decay measurements, and variable magnetic field Hall effect analysis. For samples grown at 70°C, the measured values of XRD rocking curve full width at half maximum (FWHM) (116 arcsec), root mean square (RMS) surface roughness (2.7 nm), electron mobility (6.6?×?10⁴ cm² V^?1 s^?1 at 130 K), minority carrier lifetime (～?2 μs at 130 K), and background n-type doping (～?3?×?10¹⁶ cm^?3 at 130 K), indicate device-grade material quality that is significantly superior to that previously published in the open literature. All of these parameters were found to degrade monotonically with increasing growth temperature, although a reasonably wide growth window exists from 70°C to 90°C, within which good quality HgCdSe can be grown via MBE.     

Low-temperature microwave magnetoresistance of lightly doped <Emphasis Type="Italic">p</Emphasis>-Ge and <Emphasis Type="Italic">p</Emphasis>-Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>x</Subscript>

The magnetoresistance of a lightly doped p-Ge_1?xSi_x alloy is studied in the range of compositions x = 1–2 at %. The results are compared with the available data for lightly doped p-Ge. The studies have been carried out using ESR measurements at a frequency of 10 GHz in the temperature range 10–120 K. It is established that micrononuniformity in the distribution of Si in the Ge lattice (Si clusters) suppresses the interference part of the anomalous magnetoresistance and, in addition, results in an averaging of the effects of light and heavy holes. This observation suggests a sharp decrease in the inelastic scattering time in the case of a Ge_1?xSi_x solid solution as compared to that of Ge.     

Type II broken-gap GaSb<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>As<Emphasis Type="Italic">x</Emphasis>/InAs heterojunction (<Emphasis Type="Italic">x</Emphasis> < 0.15): Evolution of the band diagram for the ternary solid solution

Layers of the GaSb_{1 ? x} As _x alloy with arsenic content in the range x = 0.06–0.15 have been grown for the first time on InAs (100) substrates by metal-organic vapor-phase epitaxy. A new approach to the calculation of the band diagram of the GaSbAs alloy is suggested. It is demonstrated on the basis of magnetotransport measurements in p-GaSbAs/p-InAs heterostructures and with the method suggested by the authors for the calculation of band diagrams for alloys in the GaSbAs system that, in the composition range under study, the GaSbAs/InAs heterojunction is a type II broken-gap heterojunction.     

On the thermopower and thermomagnetic properties of Er<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Se solid solutions

The Er _x Sn_1–x Se system is characterized by a significant deviation of the temperature dependence of the differential thermopower from linearity at temperatures below room temperature and a change in the sign of the thermomagnetic coefficient. The deviation of the thermopower of Er _x Sn_1–x Se samples in the nonequilibrium state from linearity is found to be caused mainly by the entrainment of charge carriers by phonons α_ph. The statistical forces of electronic entrainment, A _ph(ε), are estimated.     

Optical Properties of Epitaxial Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>In<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sb Alloy Layers

Optical studies of unstrained narrow-gap Al _x In_{1 − x} Sb semiconductor alloy layers are carried out. The layers are grown by molecular-beam epitaxy on semi-insulating GaAs substrates with an AlSb buffer. The composition of the alloys is varied within the range of x = 0–0.52 and monitored by electron probe microanalysis. The band gap E _g is determined from the fundamental absorption edge with consideration for the nonparabolicity of the conduction band. The refined bowing parameter in the experimental dependence E _g (x) for the Al _x In_{1 − x} Sb alloys is 0.32 eV. This value is by 0.11 eV smaller than the commonly referred one.     

Metal-insulator transition in chromium-doped Pb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te alloys

The electrical properties of chromium-doped n-Pb_1?x Ge _x Te alloys (x = 0.02–0.13) have been studied. A decrease in the free-electron concentration and a metal-insulator transition are observed as the germanium content of alloys increases. This is due to the Fermi level pinning by the chromium impurity level and to the flow of electrons from the conduction band to the impurity level. The experimental data obtained are used to calculate, in terms of the two-band Kane dispersion law, the dependences of the electron concentration and Fermi energy on the germanium content in the alloy. The motion rate of the chromium-related level with respect to the conduction band bottom is determined and a model of variation of the electronic structure with the matrix composition is suggested.