SUBSTRATE TEMPERATURE AND FILM THICKNESS DEPENDENCE OF THE OPTICAL AND ELECTRICAL PROPERTIES OF AMORPHOUS As46Te46S8 THIN FILMS

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 (E-0) from 2.35 to 2.73 eV was observed when the substrate temperature T-S was varied from room temperature to 463 K (film thickness = 100 nm). In addition, E-0 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 (T-S = room temperature). The effect of T-S on the electrical properties was also studied. The electrical resistivity (rho) and the activation energy for conduction (Delta E) decreased from 7.74 x 10(5) to 6.81 x 10(2) Omega 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.