On thickness and annealing dependence of optical properties of Te67.5 Ga2.5 As30 thin film as optoelectronic material

Highlights: ► The as-prepared Te7.5 Ga2.5 As30 film shows an indirect optical transition. ► The annealed films exhibit direct optical transition. ► The transmittance of annealed films decreases due to amorphous–crystalline transition. ► The refractive index and dielectric constant are affected by the film thickness. - Abstract: The transmission and reflection spectra of the chalcogenide Te67.5 Ga2.5 As30 thin film with thickness of 150, 300 and 450 nm are measured. The formed crystalline phases due to the thermal annealing of the as-prepared film are identified by X-ray diffraction. The as-prepared films have absorption mechanism which is an indirect allowed transition with a decrease in the value of the optical energy gap (Eg) as the thickness increases. The films annealed at temperatures higher than the temperature of the onset of the crystallization have a direct allowed transition with an increase in Eg with annealing temperatures. The effect of the film thickness on the refractive index and the high-frequency dielectric constant are studied.