Temperature-dependent oxygen annealing effect on the properties of Ga₂O₃ thin film deposited by atomic layer deposition

The effects of post-deposition oxygen annealing temperature on the physical, chemical, and optical properties of gallium oxide (Ga₂O₃) films were systematically studied in this work. First, Ga₂O₃ films were deposited on Si (100) substrates by atomic layer deposition (ALD) and then annealed at 500–900 ℃, respectively. Several standard surface analysis methods were used to characterize the Ga₂O₃ films before and after annealing. X-ray diffraction (XRD) patterns illustrated that the as-deposited amorphous film transitioned to β-phase after annealing at temperatures greater than 600 ℃. Atomic force microscopy (AFM) images showed that the grain size and roughness of the films significantly increased when annealed above 700 ℃. Transmission electron microscopy (TEM) tests presented that the interface microstructure was slightly affected by the annealing process. The effects of the annealing process on optical properties were performed using photoluminescence spectroscopy (PL) and spectroscopic ellipsometry (SE). Moreover, X-ray spectroscopy (XPS) was utilized to extract the oxygen vacancy (V_O) concentration, bandgap, and the energy band alignment of Ga₂O₃. With increasing annealing temperature, it was found that the atomic ratio of O/Ga increased while V_O decreased monotonically from 47.4 % to 27.0 %. Density functional theory (DFT) simulation further accounted for energy band shifts resulting from the variation of V_O. This study provides a means to achieve high-quality β-Ga₂O₃ films, highly significant for applications of β-Ga₂O₃-based ultraviolet photodetectors and other relevant devices.