Impurity band conduction in CdHgTe crystals

Electrical conduction at 77 K in Cd_xHg_1−xTe, with the composition x ⩽ 0.2, is by electrons in the conduction band, by holes in the valence band and by holes in the impurity band. In samples with zero energy gap, x < 0.14, electrical conduction by holes in the valence band is comparable to electrical conduction by holes in the impurity band. In the open energy gap CdHgTe, electrical conduction by holes in the valence band is negligible in comparison to electrical conduction by holes in the impurity band. In CdHgTe samples, electrical conduction in the impurity band is described by the “Fermi Glass” model.     

Effect of electron irradiation on the galvanomagnetic properties of In<Subscript>x</Subscript>Bi<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>3</Subscript> semiconductor single crystals

The effect of 5-MeV electron irradiation of p-In_xBi_2?xTe₃ single crystals (x=0, 0.04, 0.07), performed at 250 K, on the galvanomagnetic properties of the crystals was studied. The irradiation was shown to change the conduction from the p to the n type. Annealing at temperatures of 310–390 K restores the conduction to the p type. The reversal of the conduction type and variation of the carrier concentration can be accounted for by an increase in the concentration of charged point radiation defects produced in In_xBi_2?xTe₃ by irradiation. Electron irradiation of p-type Te single crystals reduces the electrical resistivity without reversing the conduction type. Annealing restores the original properties almost completely.     

Cd0.9Zn0.1Te晶体的Cd气氛扩散热处理研究

将生长得到的Cd_0.9Zn_0.1Te晶体在Cd气氛下及不同的温度条件下进行了退火处理. 借助已建立的退火处理过程中Cd_1-xZn_xTe晶体材料电阻率及导电类型变化和扩散杂质的扩散系数之间关系的模型，结合实验数据，获得了1073K，973K和873K下Cd在Cd_0.9Zn_0.1Te晶体中的扩散系数，并估算了其激活能. 通过使用获得的扩散系数，研究了在不同温度及饱和Cd气氛下，退火时间对Cd_0.9Zn_0.1Te晶体电阻率分布及导电类型等的变化的影响.     

Electronic anomalous mass near the resonant acceptor level E2 from Shubnikov-de Haas measurement in Hg0.82Cd0.18Te

Shubnikov-de Haas measurements on Hg_0.82Cd_0.18Te samples at 1.8 and 4.2 K temperature are reported. The obtained effective mass is compared with the one calculated from the non-parabolic model. The discrepancy between the two values is attributed to the presence of the E₂ resonant acceptor level. The density of states induced by this virtual level in the conduction band, is strongly dependent on stoichiometry and can be adjusted by thermal annealing.     

On the superconductivity in T1BiTe2

The temperature dependence of the magnetic susceptibility of T1BiTe₂ and T1Te, in the range 0.050 to 1.5K, has been investigated. The superconducting transition in the T1Te samples at T = 0.190K is discovered. In T1BiTe₂ superconductivity has not been seen down to 0.050 K. All this shows that the superconducting transition discovered earlier by Hein and Swiggard at 0.140 K in T1BiTe₂ is characteristic of the T1Te foreign phase.     

Photoresponse of Hg1−xCdxTe n-channel MISFETs

Photogenerated currents at 77 K, when the Semitransparent gate of an Hg_1−xCd_xTe(x = 0.205) n-channel MISFET is illuminated with IR radiation of varying intensities, have been evaluated theoretically. Two different processes of excitation are considered, namely, electron-hole pair excitation across the bandgap in the depletion layer of the field-induced junction and excitation of carriers to the conduction band from surface states lying near the middle of the bandgap. The photocurrent, in this case, is primarily due to the latter process. For the sake of comparison, the drain-source current without illumination has also been calculated as a function of the gate voltage.     

Preparation and thermoelectric properties of AgPb18SbTe20−xSex (x = 1, 2, 4) materials

AgPb₁₈SbTe_20−xSe_x (x = 1, 2, 4) bulk materials were prepared by combining hydrothermal synthesis and melting. Thermoelectric properties were measured from room temperature up to 773K. The materials showed n-type conduction and exhibited degenerate semiconductor behavior. The power factors of the materials varied greatly with increase of Se content (x). Partial substitution of Se for Te in AgPb₁₈SbTe₂₀ resulted in remarkable reduction of thermal conductivity in the whole temperature range and increase of power factor at lower temperatures; therefore, the dimensionless figure of merit, ZT, was enhanced below 600K. A maximum ZT value of ∼0.82 is obtained at 523K for the AgPb₁₈SbTe₁₈Se₂ sample.     

Negative differential mobility in PbTe and PbSnTe at high electric fields

Monte Carlo calculations of hot-electron drift velocity in PbTe and Pb_0.8Sn_0.2Te at 77 K are reported. The relevant scattering mechanisms together with band-structure nonparabolicity and anisotropy are included in the calculations. A negative differential mobility (NDM) does not appear when the electrons are assumed to remain confined within the L valleys of the conduction band. On the contrary, allowing for electron transfer into the W valleys and taking suitable values of the parameters related to these valleys, an NDM appears and the threshold field for the same agrees well with the experimental data. Alloy scattering in PbSnTe is found to reduce the NDM.     

Thermoelectric properties and electronic structure of Te-doped CoSb3 compounds

Co₄Sb_12−xTe_x compounds were prepared by mechanical alloying combined with cold isostatic pressing, and the effects of Te doping on the thermoelectric properties were studied. The electronic structure of Te-doped and undoped CoSb₃ compounds has been calculated using the first-principles plane-wave pseudo-potential based on density functional theory. The experimental and calculated results show that the value of the solution limit x of Te in Co₄Sb_12−xTe_x compounds is between 0.5 and 0.7. The Fermi surface of CoSb₃ is located between the conduction band and the valence band, and its electrical resistivity decreases with increasing temperature. The density of states is mainly composed of Co 3d and Sb 5p electrons for intrinsic CoSb₃.The Fermi surface of Te-doped compounds moves to the conduction band and its electrical resistivity increases with increasing temperature, exhibiting n-type degenerated semiconductor character. Under the conditions of the experiment, the maximum value 2.67 mW/m K² of the power factor for Co₄Sb_11.7Te_0.3 is obtained at 600 K; this is about 14 times higher than that of CoSb₃.     

Theoretical investigation on the electronic and thermoelectric properties of RuSb2Te compound

The skutterudites are an excellent candidate for thermoelectric materials used in mechanic free heat pump and electric generator. Using the ab initio density functional theory we have calculated the electronic band structure and thermoelectric properties of skutterudite RuSb₂Te. RuSb₂Te compound belongs to an indirect band gap semiconductor. The density of states has a sharp upturn at the conduction band edge and is very low at the valence band top. This feature suggests that Seebeck coefficient is larger for n doped than for p doped RuSb₂Te compound. The calculated Seebeck coefficient confirms this trend. It is in a qualitative agreement with the experiments if the temperature is not too high.     

Temperature dependent photoconductivity and photoluminescence of Cd1 − xMnxTe

Photoconductivity (PC) and Photoluminescence (PL) studies of Cd_{1 − x}Mn_xTe are reported in the ranges of composition 0.15 ⪅ x ⪅ 0.40 and temperature 10 ⪅ T ⪅ 300 K. The results of this study show that p-d transitions make an important contribution to the optical properties of Cd_{1 − x}Mn_xTe in the above range of compositions. Based on UPS and an estimate of the spin-flip energy for the Mn d electrons in Cd_{1 − x}Mn_xTe from literature data we place the centers of the Mn d↑ and Mn d↓ bands contributing to the photoemission and p-d transition processes at -3.5 eV and +2.0 eV, respectively, relative to the Γ₈ valence band edge. Strong changes in both the PL and PC spectra are observed when the Γ₆ conduction band edge shifts through the Mn 3d↓ levels. This explains the specific temperature dependence of the PC for x = 0.32 and the strong increase in the normalized intensity of the PL band at 2.0 eV at x ⪆ 0.35. The shift in the binding energy of the excitonic contribution to the PC with temperature agrees well with the model of Golnik on interactions of the excitons with the Mn²⁺ spins.     

Superconductor-insulator transition in (PbzSn1−z )0.84In0.16Te

The superconductor-insulator transition that occurs at liquid helium temperatures in the (Pb_zSn_1?z )_0.84In_0.16Te semiconductor system with varying lead concentration z = 0.5–0.9 is experimentally investigated. The transition is attributed to the change in the energy characteristics of In impurity centers due to the variation in the amount of lead. The insulator state appears with the transition from the mixed band-impurity conduction, which is characterized by resonant scattering of carriers into the quasilocal indium impurity states, to the hopping conduction between indium impurity states. The sample with z = 0.8 is found to exhibit a variable range hopping conduction described by Mott’s law. Factors that lead to the hopping conduction via impurity states are considered.     

Theory of magnetic susceptibility of the narrow-gap semiconductors Pb(Sn)Te

The nonoscillating singular part of the susceptibility of Pb_1?xSn_xTe alloys is calculated. The dependence on the composition x, temperature and the carrier concetration is explained by the existence of the valence band, separated from the conduction band with a small energy gap.     

Electrical properties of tellurium clusters on the void sublattice of an opal crystal: The important role played by the Te-SiO2 interface

The temperature dependences of electrical resistivity and of the Hall effect of nanocluster tellurium crystals obtained by filling the voids in a dielectric (opal) matrix with a melt of pure and doped Te were studied. The Hall hole concentration p _eff was found to increase anomalously (by more than two orders of magnitude) in a sample prepared from pure Te and cooled to helium temperatures. At T=1.45 K, the hole concentration in this sample was p _eff?6×10¹⁷ cm^?3. At the same time, the Hall effect in this sample was observed to reverse sign at T?200 K from positive for T<200 K to negative at higher temperatures. This implies a low impurity concentration (N _A is less than at least 10¹⁵ cm^?3). A nanocluster crystal of doped Te does not exhibit this anomaly; here, we have p _eff?6×10¹⁷ cm^?3 throughout the temperature region covered, as in the original Te. These features are assigned to the formation of a two-dimensional conducting accumulation layer near the Te-amorphous SiO₂ (the opal material) interface at low temperatures; such a layer determines the low-temperature properties of nanocluster crystals prepared from pure Te. Actually, we obtained a model of a three-dimensional structure formed from a two-dimensional film.     

低补偿度n-Hg1-xCdxTe的磁致金属-绝缘体相变和相变后的温度激活输运行为

报道了ｘ＝０．２１４组份、低补偿度（Ｋ《１）ｎ－Ｈｇ_1-xＣｄ_xＴｅ晶体在０．３─３０Ｋ温度范围，０─７Ｔ强磁场下的横向磁阻、电子霍耳迁移率、霍耳系数测量结果，观测到了磁致金属－绝缘体相变和相变后的温度激活输运行为。分析实验数据，提出：低补偿度、组份：ｘ＝０．２附近的ｎ－Ｈｇ_1-xＣｄ_xＴｅ，磁致金属－绝缘体相变（ＭＩＴ）发生的机理是载流子在浅施主杂质态上的磁冻结；发生磁冻结的前提是热冻出（ｔｈｅｒｍａｌ ｆｒｅｅｚｅ 关键词：     

129Te Mössbauer emission spectroscopic study of the V-Te system: V3Te4, V5Te8 and VTe2 phases

The hyperfine interaction in the VTe system (V₃Te₄, V₅Te₈ and VTe₂ phases) was studied by means of the ¹²⁹Te Mössbauer emission spectroscopy. The transferred magnetic hyperfine field at the ¹²⁹I site was observed at 16K for the V₅S₈-type V_2.60Te₄ which has T_N at 52K. It was found that the ionicity estimated from the isomer shift decreases with decreasing the vanadium content, which is in better agreement with the earlier results on similar chalcogenide systems such as CrTe.     

First principle electronic structure calculations of ternary alloys Hg1−xMnxTe in zinc-blende structure

We have investigated the structural, electronic, magnetic and optical properties of Hg_1?xMn_xTe in the zinc-blende phase for 0≤x≤1. The calculations were performed by using the full potential linearized augmented plane wave plus local orbitals method within the framework of the density functional theory. The lattice constants of Hg_1?xMn_xTe at different Mn concentrations exhibit Vegard's law perfectly. For spin-up channel the Mn 3d bands are occupied and mixed with the Te 5p bands whereas for spin-down channel the Mn 3d bands are unoccupied. The values of the p–d exchange splitting energy, ?_x(pd) as produced by the Mn 3d states are given. The contribution of the valence band and the conduction band in the process of exchange and splitting is described by the exchange coupling constants N₀α and N₀β. Due to p–d hybridization the magnetic moment of the Mn atom reduces, which results in small local magnetic moments on the non-magnetic Hg and Te sites. The potential applications of Hg_1?xMn_xTe in infrared device have been discussed on the basis of its optical properties.     

The performance of Hg1−xMnxTe photodiodes

The intrinsic carrier concentration and carrier lifetime in Hg_1−xMn_xTe are calculated for the temperature range 77–300 K and the compositional range 0.07 ⩽ x ⩽ 0.20. The influence of different junction current components on the R₀A product of p⁺−n photodiodes at 77 K is analysed. The highest observed R₀A values are determined by the generation-recombination current in the depletion layer. The comparison between results of calculations and the experimental data shows potential possibilities for constructing higher quality Hg_1−xMn_xTe photodiodes.     

Cd1－xZnxTe晶体的In气氛扩散热处理研究

为了满足辐射探测器件的需要，将生长得到的Cd_1-xZn_xTe晶体在In 气氛下进行退火处理能有效提高晶体的电阻率等性能. 退火处理过程的实质是一个扩散过程 ，因此研究扩散系数与Cd_1-xZn_xTe晶体的性能特别是电阻率变化之 间的关系具有重要的意义. 建立了退火处理过程中Cd_1-xZn_xTe晶体 材料电阻率及导电类型变化与杂质的扩散系数之间关系的模型.结合实验数据，获得了10 关键词： CdZnTe 热处理 In气氛 扩散系数     

Magnetic ordering in Fe<Subscript>1.087</Subscript>Te under pressure

The crystal and magnetic structures of Fe_1.087Te have been studied by neutron powder diffraction in the temperature range from 1.7 to 80 K at pressures of  ≈0.4 and ≈1.2 GPa. No symmetry change of the tetragonal paramagnetic ambient pressure phase (space group P4/nmm) was observed for temperatures above 60 K and pressures up to  ≈1.2 GPa. A novel pressure-induced phase of Fe_1.087Te having orthorhombic symmetry (space group Pmmn) and incommensurate antiferromagneticbicollinear order was observed in the temperature range from 50 to 60 K at  ≈1.2 GPa. The known monoclinic ambient pressure phase of Fe_1.087Te (space group P2 ₁/n) with commensurate antiferromagnetic order was found to be stable up to at least  ≈1.2 GPa at low temperature.