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Abstract
Bulk Ge20Te80 and Ge40Te60 alloys were prepared using the melt-quench technique. Thermally evaporated films were deposited at room temperature and different substrate temperature. Increasing the substrate and annealing temperature was found to increase the width of localized states tails and consequently decrease the optical gap of the investigated film. The structure transformations occurred in the as-deposited Ge20Te80 and Ge40Te60 films as a result of heat treatment or from depositing the films at different substrate temperatures were traced using X-ray diffractometry, scanning electron microscope and transmission electron microscope. The electrical data indicated that the values of N(EF) were increased while R and W were decreased with increasing the annealing and /or substrate temperature of the investigated Ge20Te80 films.