The Effect of Annealing Ambience on the Material and Photodetector Characteristics of Sputtered ZnGa(2)O(4) Films

Spinel ZnGa(2)O(4) films were grown on c-plane sapphire substrates at the substrate temperature of 400 °C by radio-frequency magnetron sputtering. Post thermal annealing was employed at the annealing temperature of 700 °C in order to enhance their crystal quality. The effect of thermal annealing on the microstructural and optoelectronic properties of ZnGa(2)O(4) films was systematically investigated in various ambiences, such as air, nitrogen, and oxygen. The X-ray diffraction patterns of annealed ZnGa(2)O(4) films showed the crystalline structure to have (111) crystallographic planes. Transmission electron micrographs verified that ZnGa(2)O(4) film annealed under air ambience possesses a quasi-single-crystalline structure. This ZnGa(2)O(4) film annealed under air ambience exhibited a smooth surface, an excellent average transmittance above 82% in the visible region, and a wide bandgap of 5.05 eV. The oxygen vacancies under different annealing ambiences were revealed a substantial impact on the material and photodetector characteristics by X-ray photoelectron spectrum investigations. ZnGa(2)O(4) film exhibits optimal performance as a metal-semiconductor-metal photodetector when annealed under air ambience. Under these conditions, ZnGa(2)O(4) film exhibits a higher photo/dark current ratio of ~10(4) order, as well as a high responsivity of 2.53 A/W at the bias of 5 V under an incident optical light of 240 nm. These results demonstrate that quasi-single-crystalline ZnGa(2)O(4) films have significant potential in deep-ultraviolet applications.