Conductance asymmetry of a slot gate Si‐MOSFET in a strong parallel magnetic field

We report measurements on a Si‐MOSFET sample with a slot in the upper gate, allowing for different electron densities n_1,2 across the slot. The dynamic longitudinal resistance was measured by the standard lock‐in technique, while maintaining a large DC current through the source‐drain channel. We find that the conductance of the sample in a strong parallel magnetic field is asymmetric with respect to the DC current direction. This asymmetry increases with magnetic field. The results are interpreted in terms of electron spin accumulation or depletion near the slot.     

Determination of the impurity concentration in heavily doped inhomogeneous semiconductors from the measurement of the low-temperature conductivity

A method has been developed for determining the effective concentration of shallow impuritiesN ^* reponsible for the low-temperature conductivity in the vicinity of the metal-insulator transition for inhomogeneous samples of n-Ge:As. The method is based on the measurement of two ratios of sample resistance -R(4.2 K)/R(300 K), =R(2.0 K)/R(4.2 K) and the conductivity (4.2 K). The next step consists of plotting and (4.2) vs . Assuming that is the most reliable parameter, one can calculate, after an averaging procedare, the corrected values of ^*, ^*(4.2) and the resistivity at room temperature ^*(300)=[ ^{* *}(4.2)]^–1. Finally, using the known dependence (300)=f(N) for homogeneous samples, one can obtain the values ofN ^*. The dependences ofN ^* on and on are plotted. The scaling behavior of the conductivity of the Ge:As samples with corrected values of ^*(4.2) andN ^* has been observed down toT=100 mK.     

Role of electron “lakes” in the negative magnetoresistance effect in the region of Mott hopping conductivity

It is shown for doped and compensated germanium that the appearance of negative magnetoresistance under the conditions of Mott hopping conductivity may be due to the presence of a nonuniform spatial distribution of the electron density, the temperature at which the effect appears apparently being determined by the temperature at which the electron gas condenses into electron “lakes.” A “dead zone” effect was also observed in weak magnetic fields, the threshold field increasing with the nonuniformity of the electron distribution. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 3, 187–191 (10 February 1996)     

Irradiation of germanium nanocrystals with reactor neutrons

The effect of reactor neutron irradiation on the structure of germanium nanocrystals ion-implanted into an amorphous silicon dioxide film was studied using laser Raman scattering, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The sample irradiation with a high dose of fast reactor neutrons resulted in lattice destruction and amorphization of a part of nanocrystals, leaving off a significant part well retained. Thus indicating that this nano-based material may have potential for the fabrication of devices operating under extreme conditions. Radiation defect annealing and full restoration of the nanocrystal structure were observed at 800°C; however, the average size of nanocrystals and their spatial distribution were changed.     

Neutron transmutation doping in semiconductors: Science and applications

Different aspects of neutron transmutation doping (NTD) of silicon and germanium are considered, with a special emphasis on the contribution by scientists of the Ioffe Physicotechnical Institute, Russian Academy of Sciences, to the solution of these problems. Fundamental studies related to determination of the cross sections of thermal-neutron capture by isotopes of semiconducting materials, annealing of radiation defects produced by fast reactor neutrons, and the use of NTD for probing the structure of the Ge impurity band are reviewed. Problems involved in industrial-scale production of NTD-Si, application of NTD-Si and NTD-Ge to fabrication of power thyristors, nuclear-particle and IR detectors, deep-cooled thermistors, and bolometers are discussed. The paper concludes with a consideration of prospects in the application of NTD-Si and NTD-Ge based on the use of materials with a controlled isotopic composition. Fiz. Tverd. Tela (St. Petersburg) 41, 794–798 (May 1999)     

Hopping spectroscopy in doped germanium near the metal-insulator transition

The density of states (DOS) in the vicinity of the Fermi level controls all transport phenomena at low temperatures near the metal-insulator transition (MIT). The well-known method for DOS-determination on the metallic side of the MIT, the so-called “tunneling spectroscopy”, is inapplicable on the insulating side because of the high sample resistance at low temperatures. In this work a new method for DOS-determination on the insulating side is presented. The method is based on the measurements of variable range hopping (VRH) resistance in magnetic fields. By analogy this method can be called “hopping spectroscopy”.     

Photoconductivity decay model in a-Si: H at low temperatures

Photoconductivity decay from steady-state level can be explained in terms of tunnel recombination through randomly distributed localized states in mobility gap. The calculations shows a good agreement between experiment and theory in the range of several orders of magnitude.