Structural evolution and thickness-dependant optoelectronic properties in thermally evaporated silver telluride thin films

Abstract

Silver telluride (Ag₂Te) thin films of thickness ranging from 25 to 150 nm have been prepared by thermal evaporation technique. Deposition of Ag₂Te thin films is accomplished at 1075 K, on an ultra-clean glass substrate, kept within a resistive heating thermal evaporator under a pressure of less than 10^–5 mbar. X-ray diffraction (XRD) study, scanning electron microscopy (SEM), energy-dispersive microanalysis (EDAX) and UV spectroscopy are employed for structural, chemical and optical property characterisation. XRD observation suggests that silver telluride thin films become completely crystalline beyond a 100 nm film thickness. Films of lower thickness resemble amorphous structure. Both XRD and SEM results demonstrate that partial decomposition of Ag₂Te has taken place during thermal evaporation. SEM study confirms that the surface of synthesised thin films is quite smooth. The results of UV spectroscopy establish that the band gap of Ag₂Te thin films lies within 1.4–1.7 eV. High absorption coefficient in UV region confirms that the Ag₂Te thin films exhibit direct band transition. Moreover, the optical band gap of thermally evaporated Ag₂Te thin films varies with the thickness of the thin films. I–V characteristics study demonstrates that silver telluride thin films are highly conducting in the presence of light and is supposedly a good candidate material for solar cell application.