Preparation and characterization of co-evaporated a-GaAs films

Abstract

Amorphous GaAs films were prepared from their constituents using the co-evaporated technique. The electrical and optical characterization of the prepared films have been carried out for the as-deposited (fresh), aged as well as for films annealed at 150 and 200 °C, Results of the temperature dependence of dc conductivity, in the range from −120 to 150 °C, are given and discussed. For nearly stoichiometric a-GaAs films and above RT the conduction mechanism is found to be thermally activated. In the low temperature range, the conduction is due to variable-range hopping of localized states at the Fermi level. A correlation between the optical and the electrical results, in view of the current structural models, brings about a shift in the valence band edge to high binding energies causing an increase in the optical gap of the as-deposited a-GaAs films upon annealing.