Optical absorption and electrical conductivity of amorphous AsTeGe thin films

Abstract

Optical absorption measurements have been made on As 46Te 46Ge 8 amorphous films with thickness 85–125 nm. The measurements were carried on as-prepared and annealed specimens. The mechanism of the optical absorption follows the rule of non-direct transition. The optical energy gap ( E 0) increases with increasing the annealing temperature up to 473 K, followed by a sharp decrease with increasing the annealing temperature above the glass transition temperature. Electrical conductivity was measured in the temperature range 80–300 K. The effect of heat treatment on the activation energy (Δ E) for conduction and the density of localized states at the Fermi level N( E F) was studied. The electrical measurements show annealing-dependent conductivity and exhibit two types of conduction channels that contribute two conduction mechanisms. Transmission electron microscope (TEM) investigation indicates the separation of crystalline phases after annealing at temperatures higher than 473 K. The results were discussed on the basis of amorphous–crystalline transformation.