Recrystallization behavior, oxygen vacancy and photoluminescence performance of sputter-deposited Ga2O3 films via high-vacuum in situ annealing

Ga2O3 films were deposited on Si substrates through radio-frequency magnetron sputtering at room temperature and were annealed in situ in a high-vacuum environment. The as-deposited Ga2O3 film exhibited an island-like surface morphology and had an amorphous microstructure, with a few nanocrystalline grains embedded in it. After high-temperature in situ annealing, the films recrystallized and exhibited coalesced surfaces. Because of the thermally driven diffusion of Ga, the interfacial layer between Si and Ga2O3 was composed of SiGaOx. Compared with ex situ annealing in air, in situ annealing in high vacuum is more advantageous because it enhances surface mobility and improves the crystallinity of the Ga2O3 films. The higher oxygen vacancy concentration of in situ annealed films revealed that oxygen atoms were easily released from the Ga2O3 lattice during high-vacuum annealing. Photoluminescence (PL) spectra exhibited four emission peaks centered in ultraviolet, blue, and green regions, and the peak intensities were significantly enhanced by thermal annealing at >600 °C. This work elucidates the effect of the in situ annealing treatment on the recrystallization behavior, interfacial microstructure, oxygen vacancy concentration, and PL performance of the Ga2O3 films, making it significant and instructional for the further development of Ga2O3-based devices.