Amorphous Thin Films
Abstract
The optical and transport properties of the binary amorphous systems Sb-Se, Ge-Se, and Ge-Te, have been investigated as a function of composition. Essentially the whole amorphous phase of each system was prepared in a single evaporation by an elongated substrate coevaporation technique. The optical band gap varied fairly smoothly between the values for amorphous end components. Most films exhibited lnσ vs T−1 relationships. Except for the Sb-Se system, the σ0 values lay in the hopping conductivity range. Those Ge-chalcogenide films showing lnσ vs T−(1/4) hopping conductivity behavior generally converted to a T−1 variation after annealing. The thermal activation energies and thermo-emf measurements showed the Fermi levels to be fixed well away from the band edges in the forbidden gap. Delocalization of states in the gap of α-Ge with increasing chalcogen content was not observed. The results have been interpreted in terms of chemical bonding.