Optical, photo-acoustic and electrical switching studies of amorphous GeS2 thin films

Abstract

This paper reports optical, photo-acoustic and electrical switching investigations of GeS2 amorphous thin films of different thicknesses, deposited on glass substrates in vacuum. The Tauc parameter (B 1/2) and Urbach energy (E U) have been determined from the transmittance spectra, to understand the changes in structural disorder; it is found that B 1/2 increases whereas E U decreases as the thickness of the films increases. Based on the results, it is suggested that bond re-arrangement, i.e. transformation from homopolar bonds to heteropolar bonds, takes place with increase in thickness. The thermal diffusivity values of GeS2 thin films also show the presence of a chemically ordered network in the GeS2 thin films. Further, it is found that these films exhibit memory-type electrical switching. The observed variation in the switching voltages has been understood on the basis of increase in chemical order.