CONDUCTION MECHANISM OF HIGHLY DISORDERED SEMICONDUCTORS (A POSSIBLE MODEL FOR SEMICONDUCTING GLASSES) .2. INFLUENCE OF CHARGED DEFECTS

The band perturbation due to a high density of charged defects is discussed, and it is shown that the saddle point between Coulomb‐repulsive centers can act as a potential barrier, above which conductivity takes place, if the average distance between these saddle points is small compared to the mean free path of the carriers. For a defect density of 1020 cm−3 the saddle points lie ≈ 0.25 eV from the respective band edges and are an average of 20 Å apart from each other, while the mean free path, as calculated from ion‐scattering for carriers of an energy 1 kT above these saddle points is about three times as large. These potential barriers are suggested to be responsible for the fact, that for glasses the thermal activation energy for semiconductivity is usually 0.1 to 0.3 eV larger than half the optical band gap. Copyright © 1969 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim