Effect of thickness and heat treatment on the electrical and optical properties of (Ge2S3)(1)(Sb2Se3)(1) thin films

An investigation of the electrical and optical properties of (Ge2S3)(1)(Sb2 Se3)(1), Sb2Se3, and Ge2S3 thin films prepared by thermal evaporation havin g different thicknesses and annealing temperatures has been carried out. Th e structure of synthesised glass and thin films were characterised by X-ray diffraction (XRD). The electrical conductivity was measured in the tempera ture range 300-498 K and thickness range 48.1-401.4 nm. The effect of the t hickness and heat treatment on the activation energy DeltaE for de conducti vity and the density of localised states at the Fermi level N(E-f) were stu died. The electrical conductivity measurements depend on the thickness and annealing temperature and exhibit two types of conduction channels that con tribute to two conduction mechanisms. Optical absorption measurements have been made on as-deposited and annealed films for (Ge2S3)(1)(Sb2Se3)(1), Sb2Se3 and Ge2S3 amorphous thin films. Th e mechanism of the optical absorption follows the rule of direct forbidden transition. The optical energy gap (E-opt) increased from 1.37 to 1.80 eV w ith increasing the thickness. Also E-opt increases with increasing the anne aling temperature up to 423 K, then decreases with increasing the annealing temperature. This behaviour is similar to the optical measurements of the system Sb2Se3 where Eopt decreases rapidly with increasing the annealing te mperature above the glass transition. This effect is interpreted in terms o f the density of state model proposed by Mott and Davis. (C) 2001 Elsevier Science B.V. All rights reserved.