ac band conductivity in compensated semiconductors with potential fluctuations

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Abstract
In compensated semiconductors, the occurrence of potential fluctuations which affect the local probability of ionization of deep levels cannot be ignored. These fluctuations strongly change the frequency and temperature dependence of the conductivity due to carriers in the bands. The expressions of ac and dc conductivity and of permittivity are derived in the case of a Gaussian distribution of fluctuations. It is shown that, starting from the densities and energies of impurities in the sample, the theory leads to a very accurate description of the observed conductivity in quite different cases: semi-insulating GaAs (our data), crystalline silicon (data of Pollak and Geballe). It is demonstrated that the carriers in the band are solely responsible for the observed phenomena, provided that potential fluctuations are taken into account. Band carrier conduction completely hides hopping conduction. Similar conclusions are obtained from the interpretation of data of the literature as well as our data, on amorphous semiconductors. It is inferred that the phenomena observed on a large variety of semiconductors merely reflect the same general effect of potential fluctuations on band carriers, rather than specific processes characteristic of the material.