OPTICAL-ABSORPTION AND ELECTRICAL-CONDUCTIVITY OF AMORPHOUS ASTEGE THIN-FILMS

Optical absorption measurements have been made on As46Te46Ge8 amorphou s films with thickness 85-125 nm. The measurements were carried on as- prepared and annealed specimens. The mechanism of the optical absorpti on follows the rule of non-direct transition. The optical energy gap ( E-O) 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 m easured in the temperature range 80-300 K. The effect of heat treatmen t on the activation energy (Delta E) for conduction and the density of localized states at the Fermi level N(E-F) was studied. The electrica l measurements show annealing-dependent conductivity and exhibit two t ypes of conduction channels that contribute two conduction mechanisms. Transmission electron microscope (TEM) investigation indicates the se paration of crystalline phases after annealing at temperatures higher than 473 K. The results were discussed on the basis of amorphous-cryst alline transformation. (C) 1998 Elsevier Science B.V. All rights reser ved.