The synthesis of As-Te-Ga glass films with a higher Ga ratio is essential to improve their structural and optical properties for practical applications. Herein, 150 nm thick films of As30Te55Ga15 chalcogenide were prepared utilizing the thermal evaporation technique from their bulk melted quench glass. The influences of annealing temperature ( \(\:{T}_{a}\) ) performed through the amorphous-crystalline region on the crystal structure and optical characteristics of As30Te55Ga15 films were investigated. The structure of As30Te55Ga15 films was investigated using differential scanning calorimetry and X-ray diffraction techniques, while the optical properties were accomplished utilizing a double-beam spectrophotometer. The As30Te55Ga15 glass exhibits one glass transition and crystallization phenomenon, implying its homogeneity and purity. Both as thermally evaporated and annealed As30Te55Ga15 films at \(\:{T}_{a}\) < 433 K are noncrystalline, whereas the thermal-treated films at \(\:{T}_{a}\) ≥ 433 K are semicrystalline. The annealed As30Te55Ga15 films are composed of hexagonal Ga7Te10 at \(\:{T}_{a}\) = 433 K, monoclinic As2Te3 and hexagonal Ga7Te10 at \(\:{T}_{a}\) = 473 K, and monoclinic As2Te3, hexagonal Ga7Te10 and hexagonal Ga2Te5 at \(\:{T}_{a}\) = 513 K. The change in optical constants and dispersion parameters showed two opposite trends associated with the amorphous and crystalline nature. For example, the band-gap energy demonstrated both direct and indirect optical transitions that dropped as \(\:{T}_{a}\) was elevated to 433 K, but increased again for films annealed at \(\:{T}_{a}\) = 473 K. The control of crystallite size and induced imperfections by annealing contributes to the improvement in optical characteristics.
