Inference of Sn addition on optical properties of the novel thermally evaporated thin a-Ge15Te50S35-xSnx films and some physical properties of their glasses

Abstract

In this article, the authors have prepared six novel a-Ge15Te50S35-xSnx thin-film samples 0.0≤x≤10.0at.% using the physical vapor deposition process. Thin films have been deposited on pre-cleaned glass substrates under vacuum 10−5 Pa with controlling the thickness at 300 nm. X-ray diffraction and energy dispersive X-ray analysis exhibit the amorphous nature of films with the required and selected compositional element percentages. The optical properties have been studied by analyzing the UV–Vis–NIR absorbance spectra in the range 300–2500 nm. Optical bandgap energy, Eg has been studied using Tauc plots. The Eg values found to be arising from indirect allowed electronic transitions and decreases from 1.301 eV to 1.031 eV as Sn-content increases from 0.0% to 10.0%. While the band-tail width is found to be increased from 229 meV to 288 meV, according to Urbach argument. The valence band, VB and conduction band, CB positions have been determined and discussed. It is found that VB potential increases from (- 0.433) eV to become (- 0.357) eV, while that of CB decreases from 0.867 eV to 0.673 eV as Sn-content percentage increased from 0.0% to 10%. Some physicochemical parameters have been also calculated and discussed by determining the mass-volume density using Archimedes' principle. The investigated parameters have shown strong dependency on the Sn-content. Studied optical and physicochemical properties show that these samples can be used in many optoelectronic applications like ultra-continuum infrared sources, optical infrared detectors, photovoltaic and energy applications.