Thin films of As46Te46S8 with different thicknesses were prepared via thermal evaporation
onto chemically cleaned glass substrates at different temperatures. X-ray diffraction of the
deposited film at room temperature revealed the formation of an amorphous structure. In
addition, the selected-area electron diffraction (SAED) patterns confirmed the amorphous
phase. The mechanism of the optical absorption was observed to follow the rule of direct
transition. An increase in the optical gap (E0) from 2.35 to 2.73 eV was observed when the
substrate temperature TS was varied from room temperature to 463 K (film thickness = 100
nm). In addition, E0 was observed to be dependent on the film thickness and increased
from 1.7 to 2.38 eV when the film thickness was increased from 35 to 135 nm (TS = room
temperature). The effect of TS on the electrical properties was also studied. The electrical
resistivity (ρ) and the activation energy for conduction ( E ) decreased from 7.74 x105 to
6.81 x 102 Ω cm and from 0.55 to 0.15 eV, respectively, when TS increased from room
temperature to 448 K (film thickness = 100 nm). The Mott and Davis model for the
density of states in amorphous solids was used to interpret and discuss the results.