Effects of Post-Annealing Temperature on the Properties of β-Ga2O3 Thin Films Prepared by Spray Pyrolysis

Ga2O3 polycrystalline thin films were deposited by spray pyrolysis method. The films were post-annealed at 700, 900, and 1100 degrees C for 2 h, then the crystal structure, surface morphology and optical properties of the films were studied. As the post-annealing temperature increases, the average crystallite size of the film increased from approximately 6 to 21 nm, and the FWHM of rocking curve for the (400) plane of the beta-Ga2O3 decreased from 1.29 degrees to 0.38 degrees. The increase of post-annealing temperature controls phase formation in the films. When post-annealed at 700 degrees C, the Ga2O3 film is not completely transformed into beta phase. While post-annealed at temperatures >= 900 degrees C, the Ga2O3 in the films is all beta-Ga2O3. Additionally, the increase in post-annealing temperature induced changes in the micro-strains of Ga2O3 films, which resulted in a reduction of the bandgap. These findings highlight the critical role of post-annealing temperature in controlling the structural and optical properties of Ga2O3 thin films, making it a key parameter for improving the quality of beta-Ga2O3 films.