Effect of Thermal Annealing on Structure and Optical Properties of Amorphous As30Te64Ga6 Thin Films

The impact of thermal annealing on the structural, linear, and nonlinear optical characteristics of the thermal evaporated As30Te64Ga6 thin films (thickness of 150 nm) was investigated. X-ray diffraction and scanning electron microscope results indicated that the thermally evaporated film was noncrystalline, while the annealed As30Te64Ga6 films were crystalline. The optical constants and parameters were evaluated using a spectrophotometer and measurements were performed at a wavelength of 200-2400 nm. The optical bandgap showed direct and indirect transitions which decreased as the annealing temperature increased up to 433 K and thereafter increased; while the change in the Urbach energy showed a contrary attitude. Linear and nonlinear refractive index, extension coefficient, optical density, optical and electrical conductivities, nonlinear susceptibility and optical surface resistance were found to be greatly influenced by annealing temperature and were also dependent on the energy of the incident waves. The obtained results were needed for a better basic understanding revealing possible optoelectronic applications of the thermally evaporated As30Te64Ga6.