Electrical transport measurements in a quasi-onedimensional semiconductor ZrS3

We have used the technique of chemical vapour transport to prepare needle shaped single crystal of ZrS₃. Results of the measurements of d.c. resistivity. Hall coefficient and thermoelectric power of the temperature range 100–500 K are reported. All the samples exhibited semiconducting behaviour with a room temperature resistivity of about 15 Ω-cm and an activation energy of 0.20±0.02 eV. Room temperature thermoelectric power is -850 μVK^?1 and the dominant carriers are electrons. The thermoelectric power varies as (1/T), a behaviour associated with a typical semiconductor. Mobility at low temperatures is limited by ionized impurity scattering and is given by μ₁ = 6.5 × 10^?2T^3/2 cm²V^7-1 sec^?1. At high temperatures, phonon scattering is dominant and the mobility is given by μ₂ = 1.35 × 10⁺⁵T^?32 cm²V^?1 sec^?1.     

一种测定某些离子导体的导电基本参数的新方法

利用低频交变电场在某些离子导体中能引起偏振态改变的光衍射特性,发展了一种测量这些离子导体的导电基本参数的新方法,并且用它测定了α-LiIO₃单晶的基本离子导电参数,测得其载流子的迁移率激活能E_μ=0.36eV;夫仑克耳缺陷的形成能为E_M=0.59eV;300K时正、负载流子的数密度均为1.6×10¹⁷cm^-3,相对浓度均为1.07×10^-5;当所加电场反平行于晶体的自发极化强 关键词：     

AlGaN/AlN/GaN结构中二维电子气的输运特性

对使用金属有机物汽相沉积法生长的AlGaN/AlN/GaN结构进行的变温霍尔测量，测量结果指出在AlN/GaN界面处有二维电子气存在且迁移率和浓度在2K时分别达到了1.4×10⁴cm²·V^-1·s^-1和9.3×10¹²cm^-2，且在200K到2K范围内二维电子气的浓度基本不变，变磁场霍尔测量发现只有一种载流子(电子)参与导电.在2K温度下，观察到量子霍尔效应，Shubnikov-de Haas (SdH) 振荡在磁场约为3T时出现，证明了此结构呈现了典型的二维电子气行为.通过实验数据对二维电子气散射过程的半定量分析，推出量子散射时间为0.23ps，比以往报道的AlGaN/GaN结构中的散射时间长，说明引入AlN层可以有效减小合金散射，进一步的推断分析发现低温下以小角度散射占主导地位.     

The role of anion vacancy migration in lead halide photolysis

From the electrical conductivity of meltgrown Pb₂NaI single crystals for the first time mobility of the iodide ion vacancies along the c-axis is calculated (temperature region 340–540 K). It is shown that the transition from the colour centre mode (CCM) to the print-out mode (POM) of the photolysis of Pb₂ (X = Cl, Br, I) occurs when the anion vacancy mobility in PbCl₂ and PbBr₂ exceeds the value 1.0 × 10^?8cm²V^?1sec^?1, and in PbI₂ the value 8.1 × 10^?8cm²V^?1sec^?1.     

Mobility of positrons in silicon

The drift velocity v₊ of positrons in Si has been measured by observing the Doppler shift of the annihilation γ's. The electric field dependence of v₊ yields the positron mobility μ₊: at 80 K μ₊=460±20 cm²V^-1 sec^-1 and at 184 K μ₊=173±15 cm²V^-1 sec^-1.     

Drift mobility measurements in melt-grown baryum titanate

Drift mobility measurements in melt-grown BaTiO₃ single crystal have been performed using the Spear method. The mobility of (3 ± 1) × 10^?3 cm²V^?1 sec^?1 at room temperature is found to be thermally activated, with an activation energy of 0.15 ± 0.04 eV. Two interpretations are investigated to explain these results: trapping effects due to oxygen vacancies or small polaron hopping.     

Quantum oscillations in an inversion layer on p-PbTe

We report the observation of a variable density inversion layer on p-PbTe. The carriers in the inversion channel are found to have a mobility on the order of 250,000 cm² V^-1 sec^-1. Shubnikov-de Haas oscillations in the channel conductivity were measured in magnetic fields up to 6 T. From the observed periodicity we conclude that the oscillations represent only a fraction of the total number of electrons in the channel.     

UV-induced double injection in α-sulfur single crystals

The I–V characteristics of the UV-induced double injection of carriers into sulfur single crystals are reported. These characteristics display a quadratic behavior as a function of the electric field up to E≈7×10³$\text{Volts}\text{cm}$ where it changes to a cubic law dependence. The V² branch can be accounted for by means of the one carrier space charge limited current. The cube law dependence arises as a result of the recombination limited two-carrier injection according to the model of Lampert and Mark. We estimate values for the common lifetime τ = 4.8×10^?3 sec, and the trap modulated mobility of holes $\text{μ}{}_{\mathrm{<mtext>h</mtext>}}\text{θ}{}_{\mathrm{<mtext>h</mtext>}}\text{=8.9×10}{}^{\mathrm{?6}}\text{cm}{}^2\text{V sec}$.     

Charge carriers dynamics in PEO + NaSCN polymer electrolytes

Sodium-ion-conducting poly(ethylene oxide) (PEO)-based solid polymer electrolyte films mixed with salt sodium thiocyanate (NaSCN) have been prepared by solution-cast method. Films were characterized in detail using optical microscopy, differential scanning calorimetry, and impedance spectroscopy. The drop in ionic conductivity with increasing salt concentration is supported by a decrease in number of charge carriers. Dielectric constant is supported by decreases in numbers of charge carriers and increase in mobility. The maximum ionic conductivity and number of charge carriers for material are found 9.86 × 10^?6 S/m and 1.21 × 10²⁰, respectively, for weight % ratio (95:05) of PEO:NaSCN polymer salt complex. The maximum mobility of material is found 2.58 × 10^?6 m²/Vs for weight % ratio (80:20) of PEO:NaSCN polymer salt complex.     

Diffusivity of a two-dimensional lattice fluid: CH4 adsorbed on MgO(100)

The diffusive motions of a 0.8 layer of CH₄ adsorbed on MgO(100) are measured at 72, 88 and 97 K by quasi-elastic neutron scattering. It is shown that at 72 K the methane film is solid and its molecules perform an isotropic rotational motion. At 88 and 97 K, the adsorbed layer is in a two-dimensional fluid state in which the molecules jump between equidistant (4.21 Å) lattice sites of the MgO surface. The mean residence time has been determined ( ∼ 1 × 10 ⁻¹⁰ s at 88 K and ∼ 4 × 10⁻¹¹ s at 97 K). The corresponding translational diffusion coefficients are ∼ 5 × 10⁻⁶ cm² s⁻¹ at 88 K and 12 × 10⁻⁶ cm² s⁻¹ at 97 K. The diffusivity of this lattice fluid is compared to that of the same molecules adsorbed on graphite (0001) previously reported. The reduced mobility observed in the case of CH₄/MgO(100) is related to the important depth of the potential wells on the MgO(100) surface.     

Raman spectra in doped cadmium oxide

Raman spectra of polycrystalline CdO-samples with electron-densities between 0.8 × 10¹⁹ and 13 × 10¹⁹ cm^?3 and mobilities between 80 and 250 cm²V^?1sec^?1 were observed at 300 and 2 K. Two first order Raman peaks are found at 404 and 345 cm^?1 while the second order spectrum is interpreted as due to the following processes: 2LO(L) near 970 cm^?1, 2LO(X) near 780 cm^?1, 2TO(X) or 2TO(L) at 480 cm^?1 and TA + TO(X) at 270 cm^?1. The 2LO(L)-peak shift to lower energiesand broadens with increasing electron density. This effect cannot be explained by existing theories.     

Enhancement of the colossal magnetoresistance in Eu1 − x Ca x B6

The transport and magnetic properties of single crystal samples of substitutional solid solutions Eu_{1 ? x} Ca _x B₆ (0 ≤ x ≤ 0.26) have been studied at temperatures 1.8–300 K in magnetic fields up to 80 kOe. It has been shown that an increase in the calcium concentration results in the suppression of the charge transport accompanied by an increase in the amplitude of the colossal magnetoresistance (CMR) up to the value (ρ(0) ? ρ(H))/ρ(H) ≈ 7 × 10⁵ detected for x = 0.26 at liquid-helium temperature in a field of 80 kOe. The transition from the hole-like conductivity to the electron-like conductivity has been observed in the Eu_0.74Ca_0.26B₆ solid solution in the CMR regime at T < 40 K. The Hall mobility values μH = 200?350 cm²/(V s) estimated for charge carriers in the strongly disordered matrix of the Eu_0.74Ca_0.26B₆ solid solution are comparable with the charge carrier mobility μH = 400?600 cm²/(V s) for the undoped EuB₆ compound. The anomalous behavior of the transport and magnetic parameters of the Eu_{1 ? x} Ca _x B₆ solid solutions is discussed in terms of a metal-insulator transition predicted within the double exchange model for this system with low carrier density.     

Drift mobility and kinetics of transport of excess charge carriers in glassy CdGexAs2

Conclusions We tried to measure transient conductivity response to pulse strongly absorbed excitation (light, accelerated electrons) in sandwich type samples of glassy CdGe _x As₂ compounds. We observed the signal due to transport of free excess carriers. From analysis of experimental results we conclude that in our materials strong trapping effects are present, so the range of excited carriers is very short (10^–4-10^–3 cm) even in the highest electrical fields used (to 10⁴ V. cm^–1). Estimates of upper limit of drift mobility give the values 10^–1- 1 cm² V^–1 sec^–1. We did not succeed in determining the type of carriers which are responsible for the observed effects.     

Magneto-acoustic absorption by the electron-hole liquid in stressed germanium

We report the observation of magneto-acoustic absorption by the electron-hole liquid in a potential well in stressed germanium. This experiment confirms the metallic character of the liquid and yields direct values for the electron Fermi level ?_F = (2.6±0.1) meV and inter-carrier collision time τ = (6.0±0.5) × 10^-11sec at 1.8 K under a stress of approximately 5 kg/mm². From ?_F we deduce an electron density of n = (6.2) ± 0.4) × 10¹⁶cm^-3 at 1.8 K.     

Zeitliches Abklingen und Anisotropie von p-Terphenyl- undp-Terphenyl-Anthrazen-Mischkristallen bei Beschuß mit α-Teilchen

The time dependence of scintillation intensity from single crystals ofp-terphenyl and mixed crystals ofp-terphenyl and anthracene after bombarding with α-particles was investigated at the two temperaturesT=296 °K andT=92 °K. For the crystals ofp-terphenyl the time dependence of the scintillation anisotropy was also measured. Using the formulas given byKing andVoltz the decay curves ofp-terphenyl were decomposed into two components. Good agreement between experiment and theory was found. The ratio of the prompt intensity to the delayed intensity was determined to be 1∶2 atT=296 °K and 1∶3 atT=92 °K. The diffusion constants for triplet excitons were calculated to beD _T(296 °K)≈10^?5 cm² sec^?1 andD _T(92 °K)≈ 2×10^?6 cm² sec^?1, and the triplet-triplet interaction rate constantsχ _tt(296 °K)≈ 2.5×10^?11 cm³ sec^?1 andχ _tt(92 °K)≈0.5×10^?11 cm³ sec^?1.     

Electrical properties of the SiC/Si composite and the biomorphic SiC ceramic fabricated from spanish beech wood

A study has been made of the dependences of the electrical resistivity and the Hall coefficient on the temperature and magnetic field for the SiC/Si composite fabricated from spanish beech wood and bio-SiC, a high-porosity material formed by chemical extraction of silicon from this composite. The main charge transport parameters of these materials have been determined and analyzed. It has been shown that electric transport in bio-SiC is effected by n-type carriers with a high concentration of ～10¹⁹ cm^?3 and a low mobility of ～1 cm² V^?1 s^?1. The relations obtained have been analyzed by invoking the theory of quantum corrections to conductivity.     

Infrared spectroscopy of the intermediate-valence semiconductor YbB12

The dynamic conductivity and permittivity spectra of the intermediate-valence compound YbB₁₂ are measured in the frequency range (6–10⁴) cm^?1 (quantum energy 0.75 meV-1.24 eV) at temperatures of 5–300 K. Analysis of the spectral singularities associated with the response of free charge carriers has made it possible for the first time to determine the temperature dependences of their microscopic parameters, viz., concentration, effective mass, relaxation frequency and time, mobility, and plasma frequency. It is shown that the relaxation frequency decreases upon cooling from 300 K to the coherence temperature T ^* = 70 K for YbB₁₂, which is mainly associated with the phonon mechanism of scattering of charge carriers. For cooling below the coherence temperature T ^* = 70 K, the temperature dependence of the relaxation frequency for charge carriers of the Fermi-liquid type is found to be γ ～ γ₀ + T ², while their effective mass and relaxation time increase, respectively, to m ^*(20 K) = 34m ₀ (m ₀ is the free electron mass) and τ(20 K) = 4 × 10^?13 s, indicating the establishment of coherent scattering of carriers from localized magnetic moments of the f centers. At a temperature of T = 5 K, the conductivity spectrum contains an absorption line at a frequency of 22 cm^?1 (2.7 meV); the origin of this line can be associated with the exciton-polaron bound state. Since such a state was observed earlier in other intermediate-valence semiconductors (such as SmB₆, TmSe_1?x Te, and (Sm, Y)S), it is probably typical of this class of compounds.     

Capture cross-section and density of deep gap states in a−SiHx schottky barrier structures

Recombination of charge carriers in a?SiH_x Schottky barriers with density of states near mid-gap ranging from 2.8×10¹⁵?7×10¹⁶cm^-1eV^-1 is attributed to recombination centers with hole capture cross-section of 1.3×10^-15cm².     

厚度对MOCVD生长InN薄膜位错特性与光电性质的影响

研究了金属有机物化学气相沉积法制备的不同厚度InN薄膜的位错特性与光电性质.基于马赛克微晶模型,通过X射线衍射非对称面摇摆曲线测量,拟合出样品刃型位错密度分别为4.2×10¹⁰cm^-2和6.3×10¹⁰cm^-2,并发现样品的微晶扭转角与位错密度随薄膜厚度增加而减小.通过室温霍尔效应测量得到样品载流子浓度分别为9×10¹⁸cm^-3和1.2×10¹⁸cm关键词： 氮化铟 位错 载流子起源 局域态     

“Condensation” of impurities in semiconductors (Si + Li)

The kinetics of Li precipitation in Si at the maximum doping level was investigated. The time dependence of the electron concentration and Hall mobility in the course of annealing at 300 and 350°K turned out to differ strongly from the ordinary kinetics of solid solution precipitation. The explanation proposed for the features observed assumes the appearance of a spatially inhomogenous Li-ion distribution in the crystal and the formation of electron-ion drops with a density of ～ 2?3 × 10²⁰ cm^?3.