Electronic Transport in Semiconductor Materials

Abstract

Recent developments in research and applications of electronic transport in semiconductors are reviewed. The possibility of achieving low carrier densities, the purity and perfection of single crystals, low effective carrier masses, and high dielectric constants have established semiconductors as exceedingly versatile in contrast to metals for understanding and utilizing electronic transport. The individual electron scattering mechanisms, which determine mobilities, can be separated and studied in detail. Ionizedimpurity scattering has become of renewed interest. Hot-carrier effects, being accessible in semiconductors, have recently found a new method of investigation by means of optical excitation. Carriers far from equilibrium, such as ballistic electrons, are studied in specially structured samples. High-resistivity semiconductors still present many problems, caused by compensation, by interplay of localized versus extended states, and by very long dielectric relaxation. Interfaces have captured much of the recent attention. Grain boundaries are significant for polycrystalline silicon, as used in integrated circuits or solar cells. The transport across such boundaries is governed by thermal activation over a potential produced by localized electronic states associated with the boundary. Quantum effects and quasi-two-dimensional transport give rise to novel features at semiconductor surfaces and interfaces. Quantization can be further enhanced by magnetic fields, this twofold quantization led to a new resistance standard based only on fundamental constants.