Effect of thermal annealing on the structural and optical properties of ZnGa2O4 films deposited on sapphire by magnetron sputtering

ZnGa2O4 films were prepared on α-Al2O3 (0006) wafer at room temperature using magnetron sputtering. The impact of thermal annealing on the crystallization quality, epitaxial relationship and optical property of the films were studied in detail. XRD results showed that the crystalline quality of film was significantly improved by annealing, and the 500 °C-annealed sample presented a monocrystalline film with the best crystallization quality. The results of XRD and HRTEM revealed an epitaxial relationship of ZnGa2O4 (111)//α-Al2O3 (0006) with ZnGa2O4 [011̅]//α-Al2O3 <1̅100 > . The average transmittance of the ZnGa2O4 film in the visible region surpassed 83.1 %. The optical bandgaps of the ZnGa2O4 films annealed at 400, 500 and 600 °C were calculated to be 5.13 eV, 5.12 eV and 5.15 eV, respectively, which were much higher than the value of the as-deposited one (4.65 eV).