PREPARATION AND CHARACTERIZATION OF COEVAPORATED A-GAAS FILMS

Amorphous GaAs films were prepared from their constituents using the c o-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 degrees C. Results of the temperature dependence of de conductivity, in the range from - 120 to 150 degrees C, are given and discussed. For nearly stoichiometr ic a-GaAs films and above RT the conduction mechanism is found to be t hermally activated. In the low temperature range, the conduction is du e 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 ba nd edge to high binding energies causing an increase in the optical ga p of the as-deposited a-GaAs films upon annealing.