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.     

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.     

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.     

Electroluminescence and phototrigger effect in single crystals of GaS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> alloys

The effects of switching and electroluminescence as well as the interrelation between these effects in single crystals of GaS _x Se_1?x alloys are detected and studied. It is established that the threshold voltage for switching depends on temperature, resistivity, and composition of alloys, and also on the intensity and spectrum of photoactive light. As a result, a phototrigger effect is observed; this effect arises under irradiation with light from the fundamental-absorption region. Electroluminescence is observed in the subthreshold region of the current-voltage characteristic; the electroluminescence intensity decreases drastically to zero as the sample is switched from a high-resistivity state to a low-resistivity state. Experimental data indicating that the electroluminescence and the switching effect are based on the injection mechanism (as it takes place in other layered crystals of the III-V type) are reported.     

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.     

Influence of Composition on the Thermoelectric Properties of Bi<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Thin Films

Bi_1?x Sb _x solid solutions have attracted much attention as promising thermoelectric (TE) materials for cooling devices at temperatures below ～200 K and as unique model materials for solid-state science because of a high sensitivity of their band structure to changes in composition, temperature, pressure, etc. Earlier, we revealed a non-monotonic behavior of the concentration dependences of TE properties for polycrystalline Bi_1?x Sb _x solid solutions and attributed these anomalies to percolation effects in the solid solution, transition to a gapless state, and to a semimetal–semiconductor transition. The goal of the present work is to find out whether the non-monotonic behavior of the concentration dependences of TE properties is observed in the thin film state as well. The objects of the study are Bi_1?x Sb _x thin films with thicknesses in the range d = 250–300 nm prepared by thermal evaporation of Bi_1?x Sb _x crystals (x = 0–0.09) onto mica substrates. It was shown that the anomalies in the dependence of the TE properties on Bi_1?x Sb _x crystal composition are reproduced in thin films.     

Magnetic Properties of Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>In<Subscript>2</Subscript>S<Subscript>4</Subscript> Alloy Single Crystals

This study concerns the magnetic properties of single crystals of Fe _x Mn_{1 − x} In₂S₄ alloys. The basically antiferromagnetic character of indirect exchange interactions between Fe²⁺ and Mn²⁺ cations is established. As the concentration of Fe²⁺ cations is increased, the magnetic ordering temperature increases from ∼12 K (x = 0) to ∼22 K (x = 1). Short-range-order ferromagnetic correlations are observed. The basic magnetic phase state of the alloys is the spin glass state, with the freezing temperature increasing from ∼5 K (x = 0) to ∼12 K (x = 1). As the external magnetic field is increased, the magnetic ordering temperature slightly decreases. The most probable causes and mechanisms of formation of the magnetic state of the alloys are discussed.     

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.     

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.     

High-Temperature Transport Properties of Yb<Subscript>4−<Emphasis Type="Italic">x</Emphasis></Subscript>Sm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sb<Subscript>3</Subscript>

Polycrystalline L₄Sb₃ (L = La, Ce, Sm, and Yb) and Yb_4−x Sm _x Sb₃, which crystallizes in the anti-Th₃P₄ structure type (I-43d no. 220), were synthesized via high-temperature reaction. Structural and chemical characterization were performed by x-ray diffraction and electronic microscopy with energy-dispersive x-ray analysis. Pucks were densified by spark plasma sintering. Transport property measurements showed that these compounds are n-type with low Seebeck coefficients, except for Yb₄Sb₃, which shows semimetallic behavior with hole conduction above 523 K. By partially substituting Yb by a trivalent rare earth we successfully improved the thermoelectric figure of merit of Yb₄Sb₃ up to 0.7 at 1273 K.     

On the Dielectric Study of Se<Subscript>80−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>20</Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0, 1 and 2) Glasses

In the present paper, the dielectric parameters such as the dielectric constant ε′(ω), dielectric loss ε″(ω) and alternating current (ac) conductivity have been investigated for bulk amorphous chalcogenide Se_80?x Te₂₀Pb _x (x = 0, 1 and 2) glasses in the frequency range 10 Hz to 500 kHz and within the temperature range from 300 K to 320 K. Dielectric constant ε′(ω) and dielectric loss ε″(ω) are found to be highly frequency (ω) and temperature dependent, and this behavior is interpreted on the basis of Guintini’s theory of dielectric dispersion. The ac conductivity (σ _ac) is found to be temperature independent and obey the power law ω ^s , where s < 1 and decreases as temperature rises. The obtained results are discussed in terms of the correlation barrier hopping model proposed by Elliot. The composition dependence of the dielectric constant, dielectric loss and ac conductivity are also discussed and reported here.     

The short-wavelength edge of intrinsic photoluminescence in diluted GaN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>As<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> alloys

It is suggested that the analysis of the short-wavelength edge of intrinsic photoluminescence in diluted GaN _x As_{1 − x} alloys at room temperature be used to study the specific features of the energy dependence of the density of states in the conduction band. It is found that, in the GaN _x As_{1 − x} alloys with x ≥ 0.002, this dependence is inconsistent with the model of the anticrossing band and suggests that there are extra states. These states are thought to be the states formed in nitrogen clusters and interacting with the conduction band. The energy of these states is at least 1.45 eV above the top of the valence band.     

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.     

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.     

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.     

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.     

The electrooptic effect and anisotropy of the refractive index in Tl<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>x</Subscript>GaSe<Subscript>2</Subscript> (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 0.02) crystals

The electrooptic effect and anisotropy of the refractive index in Tl_1?xCu_xGaSe₂ (0 ≤ x ≤ 0.02) crystals are studied. It is found that, as the intrinsic absorption band of each crystal is approached, the crystal refractive index increases. It is ascertained that, if an external electric field is directed along the crystallographic c axis and light propagates along this axis, the electrooptic effect is quadratic; however, if the field is perpendicular to the c axis and the light propagates along it, the electrooptic effect is linear.     

The influence of the magnetic field on the effect of drag of electrons by phonons in <Emphasis Type="Italic">n</Emphasis>-Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te

Thermopower in n-Cd_0.2Hg_0.8Te (6–100 K) is studied. A large effect of drag of the charge carriers by phonons α_ph is found. The influence of the magnetic field H on the drag thermopower is considered. It is established that the magnetic field exerts the effect mainly on the electron component of α_ph. The data are interpreted in the context of the theory taking into account the effect of H on thermopower α_ph, in which parameter A(ɛ) proportional to the static force of the drag effect is introduced. By the experimental data α_ph(T, H), T, and H dependences A(ɛ) are determined. It is shown that, as H increases, A(ɛ) sharply decreases. This explains a decrease in α_ph in the magnetic field, power index k in dependence α_ph ∝ T ^−κ, and narrowing the region of manifestation of the drag effect. It is established that at classically high fields, the drag effect in n-Cd_0.2Hg_0.8Te does not vanish.     

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.