Impact of thermal-induced sapphire substrate erosion on material and photodetector characteristics of sputtered Ga₂O₃ films

Monoclinic β–phase gallium oxide (β-Ga₂O₃) films were deposited on c-plane sapphire substrates using a combination of sputtering and post annealing processes. The effect of thermal-induced sapphire substrate erosion on material characteristics of sputtered β-Ga₂O₃ film has been investigated. Both the furnace and rapid thermal annealing (RTA) were performed in the air ambient for the post thermal treatments. After the annealing process, all the deposited films transformed from amorphous to monoclinic crystalline structure with excellent transmittance above 80% in the visible region. Meanwhile, a thermal-induced interdiffusion phenomenon has been observed in β-Ga₂O₃/sapphire architecture, particularly for furnace-annealed samples. Even though high-temperature post thermal treatments can enhance the crystallinity of the Ga₂O₃ films continuously, a degraded photodetector performance is observed for the samples annealed above 800 °C due to the thermal-induced aluminum (Al) diffusion issue. The interdiffusion mechanism for the sputtered Ga₂O₃-on-sapphire films is proposed and its effects on material and photodetector characteristics are elucidated. An optimum metal-semiconductor-metal photodetector performance is achieved for the 800°C-RTA-treated Ga₂O₃ sample with the photo/dark current ratio of 1.78 × 10⁵ and responsivity of 0.553 A/W (at 5 V bias).