Comments on the Meyer-Neldel rule in amorphous semiconductors

In this paper, we show that the Meyer-Neldel rule can be satisfactorily explained by the temperature dependence of the fermi level. We argue that the universality of the Meyer-Neldel rule can be explained by the fact that the dangling bond is the dominant defect in amorphous silicon.     

Phonon conductivity of insulators and semiconductors

Phonon conductivity calculations for materials from groups IV, III–V, II–VI and I–VII are presented. The method uses an effective relaxation time for a phonon taking into account departure from equilibrium of all other phonons which participate in both three-phonon N- and U-processes. It is shown that an important role is played by the off-diagonal part of the three-phonon collision operator above the boundary regime. In particular it is found that the off-diagonal U-processes operator gives a negative contribution to the conductivity at high temperatures. The role of optical phonons in heat transport and in acoustic-optical phonon scattering is also studied. For materials with the mass ratio m₁/m₂ ? 1 we have used the Debye dispersion law in the ‘reduced zone’ scheme, while for materials with m₁/m₂ > 1 but <4 we have used the Debye dispersion law for the acoustic phonons and the Einstein dispersion law or the optical phonons. Inclusion of the optical phonons does not modify the temperature dependence of the conductivity but does change the magnitude significantly.     

High-frequency hopping conductivity and permittivity in compensated semiconductors

In semiconductors, high-frequency conductivity is caused by polarization reversal of the collective states of a pair of impurity atoms under the action of the random electric fields of all the impurities. A Coulomb correlation which appreciably increases the conductivity is established as a result of the statistical distribution of the particles over four levels of the diatomic system. The relaxation absorption and the permittivity of the entire pair system are calculated allowing for these statistics.     

Electrical conductivity in very anisotropic conductors and semiconductors

Summary For very anisotropic metallic and semiconducting systems it is shown that the electrical conductivity in the direction of high effective mass decreases as the number of electrons in the conduction band grows. In the other directions the conductivity behaves normally.

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Riassunto Si mostra che, per sistemi semiconduttori e metallici anisotropi, la conduttività elettrica nella direzione di massa altamente efficace diminuisce all'aumentare del numero di elettroni nella banda di conduzione. Nelle altre direzioni la conduttività si comporta normalmente.

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Резюме Для очень анизотропных металлических и полупроводниковых систем показывается, что электропропроводность в направлении большой эффективной массы уменьшается, когда число электронов в зоне проводимости увеличивается. В других направлениях проводимость ведет себя нормальным образом.

     

Theory of hopping conductivity in disordered semiconductors

The bond percolation method is used to investigate the conditions under which a linear (and not exponential) temperature dependence of hopping conductivity can be observed.Translated from Izvestiya Vysshikh Uchbenykh Zavedenii, Fizika, No.2, pp. 52–62, February, 1976.     

Breakdown of metallic conductivity in quasicrystals

In the icosahedral phases i-AlCuFe, i-AlPdMn and i-AlPdRe, the electrical conductivity is in the same range as for doped semiconductors. Strong similarities are observed between the direct and tunneling conductivity for the i-AlPdRe phase and for disordered systems on both sides of the metal–insulator (MI) transition.     

The Meyer-Neldel rule in field-effect measurements and the microscopic prefactor of the conductivity in a-Si: H

The temperature dependence of the field-effect characteristic is studied. The data are analysed on the basis of the effective density of states function obtained from the data at a single temperature. It is shown that there are four reasons for the Meyer-Neldel-like behaviour: the statistical shift of the bulk Fermi-level, the temperature shift of the conduction band, the break-down of the interface approximation and as the most important effect the explicit temperature dependence of the Fermi distribution. The energetic position of the dominant transport path, the temperature coefficients of the Fermi level and of the conduction band energies are obtained by fitting the entire set of measurements. A detailed analysis allows the determination of the microscopic prefactor of the flat-band conductivity.     

Microwave conductivity studies on some semiconductors

The cavity perturbation technique is employed for the characterisation of semiconductors at microwave frequency for its conductivity. Temperature variation of microwave conductivity studies provide the information regarding the band gap, scattering parameter and impurity ionization energy. Change in the real part of the dielectric permittivity with conductivity indicates the change in the momentum relaxation time.     

金属纳米颗粒的热导率

本文使用统计模拟方法对金属纳米颗粒的电子平均自由程进行了计算,并考察了纳米颗粒的晶格比热和声子平均群速度,最后应用动力学理论对纳米颗粒的电子热导率和声子热导率分别进行了求解.研究结果表明:具有相同特征尺寸的方形、球形纳米颗粒的无量纲电子(或声子)平均自由程比较接近.金属纳米颗粒的电子热导率远大于声子热导率;电子、声子热导率随着直径减小呈现降低趋势,而电子热导率的颗粒尺度依赖性比声子热导率更为明显;随着颗粒直径进一步减小,声子热导率与电子热导率趋于同一数量级.当纳米颗粒特征尺寸大于4倍块材电子(或声子)平均自由程,其电子(或声子)热导率的颗粒尺度依赖性将减弱.     

Charge and spin Hall conductivity in metallic graphene

Graphene has an unusual low-energy band structure with four chiral bands and half-quantized and quantized Hall effects that have recently attracted theoretical and experimental attention. We study the Fermi energy and disorder dependence of its spin Hall conductivity sigma(xy)(SH). In the metallic regime we find that vertex corrections enhance the intrinsic spin Hall conductivity and that skew scattering can lead to sigma(xy)(SH) values that exceed the quantized ones expected when the chemical potential is inside the spin-orbit induced energy gap. We predict that large spin Hall conductivities will be observable in graphene even when the spin-orbit gap does not survive disorder.     

Thermal conductivity of GaS and GaSe layered semiconductors

This paper reports on the results of experimental investigations into the thermal conductivity of GaS and GaSe layered semiconductor crystals in directions parallel and perpendicular to the crystal layers in the temperature range 5–300 K. Specific features of the thermal conductivity of these crystals are analyzed.     

Laser-induced conductivity of semiconductors at low temperatures

We consider the negative conductivity of electrons in semiconductors excited by a picosecond laser pulse at low temperatures, due to the inelastic electron-phonon collisions. For the first time, the dependence of the deformation potential on the phonon wave number is taken into account. This dependence significantly changes the region of negative electron conductivity as a function of the phonon temperature. The text was submitted by the authors in English.     

Minimum metallic conductivity in a thin crystal

Electrical conductivities of thin crystals of Bi₂(Te,S)₃ measured from 4.2°K to 300°K fall into four regions: 1) σ < 1.3×10^?5 S with positive temperature coefficient of conductivity; 2) 1.3×10^?5 S < σ < 1.4×10^?5 S with temperature independent conductivity; 3) 1.4×10^?5 S σ < 4×10^?5 S with negative temperature coefficient of conductivity, and 4) σ > 4×10^?5 S with hardly any temperature dependence. A disproportionately high fraction of samples falls into the second range; 1.3×10^?5 S < σ < 1.4×10^?5 S.     

Electrical conductivity and thermopower of metallic helium

The pair effective interionic interaction, electrical resistance, and thermopower of liquid metallic helium have been calculated over wide temperature and density ranges using the perturbation theory for the potential of electron-ion interaction. For conduction electrons, the random-phase approximation has been used taking into account the exchange interaction and correlations in the local-field approximation. The nuclear subsystem has been described by the hard-sphere model. The sphere diameter is the only parameter of the theory. The diameter and the system density at which helium is transformed from the singly ionized to doubly ionized state have been estimated based on an analysis of the pair effective interaction between helium nuclei. The case of doubly ionized helium atoms has been considered. The numerical calculations have been performed taking into account the perturbation theory in terms up to the third order. In all cases, the role of the third-order correction is significant. In the case of metallic helium, the values of the electrical resistance and its temperature dependence are characteristic of divalent simple liquid metals, as well as the dependences of the thermopower on the density and temperature.