Concentration-fluctuation model of a doped semiconductor in the nonmetallic regime: Pseudocluster investigation

Abstract

We have performed an improved unrestricted Hartree-Fock pseudocluster calculation with a correlated two-electron wave function for the $D^{-}$ state to investigate the microscopic structure of impurity bands in doped semiconductors. Though the impurity density of states and the estimated specific heat support the Mott-Hubbard-Anderson model, in the nonmetallic regime the impurity states are cluster states and a doped semiconductor can be described as statistically distributed clusters of various sizes. The distribution function of the cluster states agrees with the recent conclusion obtained from analyzing the optical, magnetic, dielectric, and transport data. A new picture of thermally activated hopping is provided which is relevant to the observed non-Ohmic conductivity and large characteristic electronic length.