Energy spectrum of charge carriers in Ag<Subscript>2</Subscript>Te

On the basis of investigations of the temperature and concentration dependences of kinetic coefficients (the Hall coefficientR, the electrical conductivity σ, and thermopower α₀) in n-type Ag₂Te, it is established that Ag atoms in Ag₂Te create the shallow donor levels located at a distance of (0.002?7 × 10^?5 T) eV from the bottom of the conduction band. It is shown that silver telluride has n-type conductivity starting with the deficiency of Ag ≥ 0.01 at % in the stoichiometric composition, and it is practically impossible to achieve the stoichiometric composition in Ag₂Te.     

Hysteresis in Ag<Subscript>2</Subscript>Te near and within the phase transition region

Electrical conductivity, the Hall coefficient, and thermoelectric power were studied and differential thermal analysis was carried out in Ag₂Te crystals near and within the range of phase transitions, in the directions of heating and cooling. A large hysteresis loop was observed. The results are discussed in terms of the theory of smeared phase transitions. Agreement between experimental data and theory is achieved in a second approximation of the inclusion function L₂(T) and its derivative with respect to temperature, dL₂/dT.     

Electron-phonon damping factor for the landau quantization of 2D electrons with a fine structure of the energy spectrum

The drift of degenerate 2D electrons in the channel of the heterojunction potential well is considered. In a quantizing magnetic field B, the electrons scan the defects of the heteroboundary, which perturb their momentum and energy equilibrium state (T, T _D ⁰ ). The stationary nonequilibrium state (T, T _D ^* ) is attained by electron-phonon relaxation in energy and momentum. The experimentally observed nonlinear dependence T_D(T) is explained by the admixture of deformation acoustic phonons to the interaction of 2D electrons with piezoelectric phonons.     

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.     

Thermoelectric figure of merit of Ag<Subscript>2</Subscript>Se with Ag and Se excess

In the temperature range of 100–300 K, the electric (σ) and thermoelectric (α₀) properties of Ag₂Se with an excess of Ag as high as ～0.1 at. % and Se as high as ～1.0 at. %, respectively, are investigated. From the data on σ, α₀, and χ_tot (thermal conductivities), the thermoelectric power α ₀ ² σ and the figure of merit Z are calculated. It is found that α ₀ ² σ and Z attain the peak values at room temperature and the electron concentration n ≈ 6.5 × 10¹⁸ cm^?3.     

Electrical and thermoelectric properties of <Emphasis Type="Italic">p</Emphasis>-Ag<Subscript>2</Subscript>Te

Temperature dependences of the Hall coefficient R, electrical conductivity σ, and thermopower α₀ are investigated in the range of 4–300 K. The specific features observed in temperature dependences R(T), σ(T), and α₀(T) are interpreted in the context of a model with two types of charge carriers.     

Relaxation of excited donor states in silicon with emission of intervalley phonons

The process of low-temperature relaxation of excited states of Group V donors in silicon due to coupling of electrons bound at Coulomb centers with intervalley phonons is analyzed. The rate of transitions from the 2p ₀ state to the group of 1s(E, T ₂) states with emission of the intervalley acoustic phonons LA-g and TA-f is calculated for the phosphorus, antimony, arsenic, and bismuth donors. It is shown that the TA-f phonons make a substantial contribution to nonradiative decay of the 2p ₀ state that controls the stimulated infrared emission of the phosphorus and antimony donors in silicon.     

Effect of a phase transition on the electron energy spectrum in Ag<Subscript>2</Subscript>S

Temperature dependences of electrical conductivity σ, Hall coefficient R, and thermopower α₀ in Ag₂S are reported. It is established that at T ≈ 435 ± 5 K, all kinetic parameters vary drastically, which is associated with a change in parameters of the conduction band. It is shown that the dispersion law of electron energy in β-Ag₂S corresponds to the Kane model.     

Electrical and thermoelectric properties of <Emphasis Type="Italic">p</Emphasis>-Ag<Subscript>2</Subscript>Te in the β phase

The conductivity σ, Hall coefficient R, and thermoelectric power α₀ of p-Ag₂Te were studied in the temperature range of 300–550 K. Inconsistency between the signs of R and α₀ was observed at 420–550 K. These results are interpreted within the two-phase model with spherical constant energy surfaces. It is established that the inconsistency between the R and α₀ signs is due to the emergence of the scattering mechanisms with the parameters r_0ac, r₀₀, and r_0d an increase of about 50% in the ratio of the effective electron and hole masses as a result of the transition α → β.     

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.     

Superconducting properties of (Pb<Subscript>0.05</Subscript>Sn<Subscript>0.95</Subscript>)Te doped with indium under conditions of hydrostatic compression

The superconducting properties of Pb_0.05Sn_0.95Te semiconductor alloy doped with 5 at % of In are investigated at a hydrostatic pressure of P < 7 kbar. At increasing pressure P > 1.35 kbar and T ≥ 1.3 K, the resistivity step to ρ = 0 in the temperature and magnetic-field dependences ρ(T) and ρ(H), which corresponds to the transition to the superconducting state, disappears. The experimental results are indicative of a decrease in the density of states at the Fermi level with increasing pressure, which can be interpreted as an indium-level shift deep into the valence band. The obtained data refine and supplement the results of studies devoted to investigation of the baric dependences of the critical parameters of the superconducting transition in (Pb _z Sn_1–z )_0.95In_0.05Te with varying lead content z.     

Thermoelectric figure of merit in solid solutions with phonon scattering by off-center impurities

The Seebeck coefficient and the electrical and thermal conductivities (S, σ, and κ) of ternary PbTe_1?xSe_x (x=0.1 and 0.3) and quaternary PbTe_1?2xSe_xS_x (x=0.025, 0.05, 0.1, and 0.15) solid solutions have been studied. Polycrystalline samples with an electron density of (0.5–5.0)×10¹⁸ cm^?3 were used; their quality was monitored by comparing the measured and calculated mobility values at 85 K. A considerable decrease in mobility and an anomalous trend in the σ(T) curve near 77 K were revealed in quaternary alloys with x?0.1; for x=0.15, unusual behavior of κ(T) was also found. According to estimates, the lattice thermal conductivity of this material is temperature-independent in the 80-to 300-K temperature range. This means that a reduction in phonon-phonon scattering with an increase in temperature is completely compensated by an increase in the scattering on impurities. The observed anomalies of σ(T) and κ(T) are considered assuming the possible of off-center location of sulfur atoms at the lattice sites. The thermoelectric figure of merit Z of the studied alloys has been determined in the range 80–300 K. In spite of decreasing mobility, the maximum Z was obtained in a quaternary compound with x=0.1: at 300 K, Z_max=2×10^?3 K^?1 with a carrier density of ～3×10¹⁸ cm^?3; at 175 K, Z_max=1.5×10^?3 K^?1 with the density decreasing to 5×10¹⁷ cm^?3. The obtained data indicate that the introduction of off-center impurities rises Z at T?300 K.     

A vacancy model of the heteropolytype epitaxy of SiC

A model for the transformation of SiC polytypes occurring during the growth of an epitaxial layer is suggested that is based on the variation over time of the concentration of carbon vacancies in a transition layer. Experimental data are analyzed in terms of this model. It is shown that the parameter η=Gτ/L _T (L _T is the thickness of the transition layer, G is the film growth rate, and τ is the lifetime of a vacancy in the transition layer) is invariant with respect to the method and temperature of the growth of the epitaxial layer. This parameter is determined only by the concentration of carbon vacancies in the substrate and in the film.     

Defects of the structure of semiconductor superlattices grown on the basis of II–VI alloys

The specific features of defects of crystal lattices in multilayer device structures containing small-period (T ? 20 nm) superlattices of type I ZnSe/Cd _x Zn_{1 ? x} Se/ZnSe/.../ZnSe/(001)GaAs and type II ZnS/ZnSe_{1 ? x} S _x /ZnS/.../ZnS/(001)GaAs are studied by the methods of X-ray diffractometry and diffraction rocking pseudocurves, and partially by the X-ray topography. According to the data of quantitative analysis of the X-ray diffraction spectra, the periods of superlattices are in the range T _I = 11.3–16.1 nm (for the compositions Cd _x Zn_{1 ? x} Se with x ₁ = 0.047 and x ₂ = 0.107) for type I superlattices and T _II = 15.6–17.2 nm for type II superlattices (for the compositions ZnSe_{1 ? x} S _x with x ₁ = 0.20 and x ₂ = 0.10). The widths of diffraction peaks from both the ZnSe layers and small-period superlattices in the diffraction rocking pseudocurves considerably exceed their widths in the X-ray diffraction spectra. This fact proves that a pronounced plastic strain with the formation of series of rectilinear dislocations in the crossing slip systems took place in the studied device structures. In order to exclude the generation of dislocations in the growth processes, it is necessary to decrease the concentration of the solid solution to the values x < 0.047 for the first type of superlattices and to the values x ? 0.062 for the second type of superlattices, and to decrease the thickness of the ZnSe and ZnS layers.     

Thermodynamic stability of bulk and epitaxial CdHgTe,ZnHgTe, and MnHgTe alloys

The thermodynamic stability of Cd_1?xHg_xTe, Mn_xHg_1?xTe, and Zn_xHg_1?xTe alloys is studied. Calculations performed in the context of the δ lattice-parameter model indicate that CdHgTe and ZnHgTe alloys are stable over the entire range of compositions at typical growth temperatures. At the same time, a miscibility gap is found in Mn_xHg_1?xTe at 0.33 < x < 1 at T = 950 K, which is consistent with the known experimental data. It is shown that the biaxial strains observed in Mn_xHg_1?xTe/CdTe and Mn_xHg_1?xTe/Cd_0.96Zn_0.04Te thin epitaxial films lead to a narrowing of the miscibility gap and to insignificant lowering of critical temperatures.     

Energy parameters of two-electron tin centers in PbSe

Relations that make it possible to use an experimentally measured temperature dependence of carrier concentration to determine the Hubbard energy U and temperature dependence of the Fermi level F for two-electron tin centers in lead selenide are derived. A study of Pb_1?x?ySn_xNa_ySe solid solutions shows that their Fermi level in the temperature region 100–600 K lies below the valence band top E _v and that their F(T) dependences are linear, with extrapolation to T = 0 yielding E _V ?F = 210±10 meV. The Hubbard energy of the two-electron tin centers in PbSe is found to be U = ?80±20 meV.     

Effect of fluctuations on electron and phonon processes and thermodynamic parameters of Ag2Te and Ag2Se in the region of phase transition

Temperature dependences of electrical conductivity σ, thermoelectric power α, results of differential thermal analysis ΔT _y , thermal conductivity χ, temperature conductivity κ, and heat capacity C _p were studied in Ag₂Te and Ag₂Se semiconductors in the region of the phase transition. Two extrema are observed in the temperature dependence χ(T): a maximum in the region of the α′ → β′ transition and a minimum in the region of the β′ → β transition; these extrema are caused by the similar dependence C _p (T). It is shown that the α → α′ and β′ → β transitions are displacement transitions, while the α′ → β′ transition is of reconstruction type. It is established that the disorder parameter η in silver chalcogenides is highly smeared in the region of the phase transition; therefore, disordering of phases at the point of the phase transition is incomplete: 73, 62, and 48% in Ag₂Te, Ag₂Se, and Ag₂S, respectively. The minimum volumes V _ph for new phases are calculated; it is shown that the value of V _ph in displacement transitions is larger than in the reconstruction-type transitions.     

Fine Structure of the long-wavelength edge of exciton-phonon absorption and hyperbolic excitons in silicon carbide of 6<Emphasis Type="Italic">H</Emphasis> polytype

The fine structure of the long-wavelength edge of the polarization spectra of exciton-phonon absorption in moderate-purity n-type 6H-SiC crystals with a concentration of uncompensated donors N_D?N_A=(1.7–2.0)×10¹⁶ cm^?3 at T=1.7 K was studied. The analysis of new special features found at the absorption edge and the reliable detection of the onset of exciton-phonon steps related to the emission of phonons from acoustical and optical branches allowed highly accurate determination of a number of important parameters such as the band gap, the exciton band gap, the exciton binding energy, and the energies of spin-orbit and crystal-field splitting of an exciton. For the first time, transitions with the emission of LA phonons to the 1S exciton state with an M₁-type dispersion law were detected in E ∥ Z(C) polarization (the electric-field vector is parallel to the optical axis of the crystal). This observation supports the previously predicted “two-well” structure of the conduction band minimum in 6H-SiC.     

Structural defects and electrical conductivity in nanocrystalline SiC:H films doped with boron and grown by photostimulated chemical-vapor deposition

The paramagnetic DB defects and dark conductivity σ_d in films of nanocrystalline hydrogenated silicon doped with boron and carbon (nc-SiC:H) and grown by photostimulated chemical vapor deposition are studied. It is shown that an increase in the doping level leads to a phase transition from the crystalline structure to an amorphous structure. The electrical conductivity increases as the doping level increases and attains the value of σ_d = 5.5 × 10^?2 Ω^?1 cm^?1; however, the conductivity decreases once the phase transition has occurred. The concentration of DB defects decreases steadily as the doping level increases and varies from 10¹⁹ cm^?3 (in the crystalline structure) to 9×10¹⁷ cm^?3 (in the amorphous structure).     

Independent operation time of photodetectors of the (3—5)-μm spectral band based on InSb and CdHgTe heteroepitaxial structures

The time of independent operation t _ind of indium antimonide photoresistors and photodiodes and photoresistors based on Cd _х Hg_1–х Te (х ~ 0.3) heterostructures deeply cooled with a Joule–Thomson throttling system is investigated. The largest independent operation time (taut ≥ 28 s) was obtained for Cd _х Hg_1–х Te (х ~ 0.3) photoresistors. Time t _ind of the photoresistors and photodiodes is found to be related to the temperature of transition of the semiconductor materials from the impurity region to the intrinsic region. The possibility of increasing time t _ind of the photodetectors by optimizing the requirements for the characteristics of InSb and Cd _х Hg_1–х Te is discussed.