Crystal Growth and Structure–Property Optimization of Thermally Annealed Nanocrystalline Ga2O3 Films

The effects of thermal annealing on the crystal chemistry, crystallization process, index of refraction, mechanical properties, and electrical characteristics of nanocrystalline Ga2O3 films was evaluated. Ga2O3 thin films were sputtered onto Si(100) substrates at 500 °C utilizing a Ga2O3 ceramic target, while postdeposition thermal annealing was performed between a range of 500–900 °C. Both structural quality and packing density of the Ga2O3 films was improved by the thermal annealing as indicated by the X-ray diffraction and ellipsometry studies. The atomic force microscopy analysis indicates that the annealing temperature has a dramatic effect on surface roughness, especially when the annealing temperature exceeds 700 °C. Corroborating with structure and morphology changes, the high values of hardness and elastic modulus are noted for Ga2O3 films annealed at higher temperatures (800–900 °C). Index of refraction (n) and extinction coefficient (k) results, and their dispersion profiles indicate that the annealing temperature strongly influences the optical properties. The refractive index values vary in the range of 1.78–1.84 (632 nm) because of the gradual improvement of structural quality, texturing, and packing density upon thermal annealing. A correlation between annealing temperature, optical characteristics, and electrical characteristics in Ga2O3 films is established.