Effect of deposition parameters on the optical energy gap and refractive index of a-Ge–Se–Te thin films

Abstract

The effect of deposition parameters, i.e. type of substrate (microscope glass, quartz and mica) and thickness (500 nm, 800 nm and 1100 nm), on the optical properties of Ge10Se90− x Te x (x = 0, 10, 20, 30, 40, 50) thin films was investigated. Thin films were deposited by the vacuum evaporation technique at a base pressure 10−4 Pa. Optical transmission measurements were used to determine the refractive index (n) and optical energy gap . Transmission spectra were obtained in the spectral range 400–1500 nm. With an increase of film thickness, the optical energy gap was found to increase, whereas no significant change was observed for the refractive index within experimental error. For different substrates used in deposition of the thin films, the refractive index follows the order n mica > n microscope glass > n quartz . The optical energy gap of films deposited on mica substrate is the smallest, whereas for microscope glass and quartz substrates it remains nearly the same.