Growth and characterization of co-sputtered Al-doped ZnGa2O4 films for enhancing deep-ultraviolet photoresponse

Abstract

Al-doped ZnGa2O4 (ZGO) films were deposited on c-plane sapphire substrates by co-sputtering of Al and ZGO targets at a substrate temperature of 400 ℃ and thermally annealed at 800 ℃ to enhance their crystalline quality. In this investigation, the DC power for metallic Al target was varied from 0 to 50 W and its effect on structural, optical, and optoelectronic properties of these films were investigated. After annealing, all films exhibited the crystalline nature with the ZGO phase. Further, this investigation revealed that the 800 ℃ annealed Al-doped ZGO film deposited with the 20 W DC power possessed the highest crystalline quality among other films along with the wide-bandgap of 5.18 eV. The X-ray photoemission spectrum measurements revealed from the Ga 2p3/2 and Al 2p core-level spectra that the Al atoms occupy the octahedral sites, which makes Al─O─Ga bonding in the ZGO network. The metal–semiconductor-metal photodetector with this annealed 20 W Al-doped ZGO film exhibited the photocurrent to the dark current ratio of 3.35 × 104 and high responsivity of 3.01 A/W (at 3 V and 220 nm), which shows the enhancement in device performance about 12 times when compared with that of annealed 0 W Al-doped ZGO photodetector.