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

Monoclinic beta-phase gallium oxide (beta-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 beta-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 beta-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 degrees 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 degrees C-RTA-treated Ga2O3 sample with the photo/dark current ratio of 1.78 x 10(5) and responsivity of 0.553 A/W (at 5 V bias). (C) 2020 Elsevier B.V. All rights reserved.