Plasma power-dependent properties of Ga-S-Se films prepared by PECVD for photodetection applications

Abstract

Ga-S-Se films have been prepared by plasma-enhanced chemical vapor deposition (PECVD). In this study, highly pure elemental gallium, sulphur and selenium with 99.9999 vol% purity were utilised as starting materials. A non-equilibrium low-temperature RF-plasma (40.68 MHz) at reduced pressure (0.1 Torr) was the initiator of chemical transformations. The effect of plasma discharge power on the properties of the deposited films was investigated. All samples exhibiting stoichiometry close to GaS_1−xSe_x c x ≈ 0.6. The results of X-ray diffraction and Raman spectroscopy indicate that the films are grown in a layered hexagonal structure with lattice parameters a = 3.68 Å и c = 15.77 Å. The surface of the prepared samples is found to be strongly dependent on the used plasma power. The analysis of the transmission spectra indicates that the energy of the indirect band gap decreases from 2.27 to 2.21 eV with increasing plasma discharge power. All samples showed clear photoluminescence peaks at 561–565 nm. Current-voltage characteristic, measured under both dark and illuminated conditions, demonstrate a pronounced photoresponse in Ga-S-Se films deposited at 50 and 70 W, which makes it possible to use such materials for the development of visible matrix photodetectors.