Abstract
Thin films of Ge
15Te
85−
x
Cu
x
of different compositions are deposited on glass substrate by the thermal evaporation method. The as-deposited Ge
15Te
85−
x
Cu
x
films of all compositions containing Cu up to 7
at% were amorphous, as examined by X-ray diffraction and electron microscopy. Annealing Ge
15Te
85−
x
Cu
x
films at 473
K produced crystalline peaks. The optical energy gap (
E
o) of the freshly deposited films as well as annealed films was determined from absorption and transmission spectra. The observed decrease of
E
o with increasing Cu content is attributed to an impurity effect. The increase of
E
o with increasing thermal annealing could be due to the reduction of the number of unsaturated defects with the decrease of the density of localized states in the band structure. The dielectric constant (
ε
∞
) and the ratio of the carrier concentration to the effective mass (
N/
m*) increase with the increase of both the Cu content and the annealing temperature.