On the possibility of the electron-hole plasma conductivity in diamond being negative
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On the Possibility of the Electron–Hole Plasma Conductivity in Diamond Being Negative A. S. Baturin, V. N. Gorelkin, V. R. Solov’ev, and I. V. Chernousov Moscow Institute of Physics and Technology, Institutskiœ per. 9, Dolgoprudnyœ, Moscow oblast, 141700 Russia Received July 31, 2007; in final form, October 23, 2007
Abstract—The mobilities of charge carriers in boron-doped diamond at low temperatures are estimated by numerically solving the Boltzmann equation for a steady-state nonequilibrium velocity distribution function of the carriers with allowance for their scattering by phonons. Estimates show that, at temperatures of up to 100 K, charge carriers with a negative mobility exist over a fairly broad (on the order of 100 K) range of their energies. In the steady-state case, the absolute mobility integrated over the distribution function turns out to be positive, but there are grounds to suppose that, in the case of an unsteady pulsed source of charge carriers, it may become negative. PACS numbers: 72.20.Dp DOI: 10.1134/S1063780X0805005X
1. INTRODUCTION Papers [1–5] considered the possible existence of an absolute negative mobility (ANM) of electrons in a plasma of noble gases with an admixture of halogens. In gases, this effect is associated with the fact that, in certain energy ranges, the cross section for transport scattering of electrons by the atoms of heavy noble gases increases sufficiently sharply with energy. The admixture of halogens was required in order to deplete the electron energy distribution in the low-energy range, in which the behavior of the cross section is normal, i.e., the cross section decreases with increasing energy. The depletion of the distribution at low energies is due to electron attachment to the atoms of a halogen. Research on the negative mobility in semiconductors was reviewed by Elesin [6]. The mechanism for the onset of the ANM of nonequilibrium electrons is considered to be their scattering by optical phonons, a process that is efficient at sufficiently high temperatures of the medium (on the order of the room temperature). At low temperatures, this mechanism does not operate. In diamond at a low temperature (T < 100 K), the charge carriers (electrons and holes) are scattered predominantly by acoustic phonons. It is expected that, for this scattering process, the frequency should increase with energy in the range of energies on the order of mc2, where m is the mass of a carrier and c is the speed of sound. A charge carrier moving with the velocity v < c cannot emit a phonon, and the collision frequency is low, but at velocities of v > c, phonons can be produced and the collision frequency increases. In analogy with the aforementioned case of a low-temperature plasma of noble gases, this behavior of the collision frequency
can lead to the onset of negative conductivity in diamond. The experimental data of [7, 8] on negative muons in diamond at T < 100 K can be interpreted as evidence for the onset of ANM under unsteady conditions. In [9], preliminary calculations
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