Molecular model of impurity bands in semiconductors

Abstract

The formalism of Matsubara-Toyozawa for impurity bands in semiconductors is extended by including the correlations between electrons and between impurities, as well as the overlap effect. The electronic correlation is introduced through an alternant molecular orbital method and the correlation between the impurities is approximated by an extended chain of hard-core pair correlation functions. The calculation with various degrees of compensation shows a reduction of the impurity bandwidth, a lowering of the Fermi energy and an increase of the DC conductivity in comparison with those derived by Matsubara-Toyozawa. We found that the electronic correlation plays the dominating role in all the results, while the effect of correlation between impurities shows up only at high impurity concentrations. The calculated DC conductivity agrees reasonably well with experiments.