Magnetron Sputter-Deposited β-Ga2O3 Films on c-Sapphire Substrate: Effect of Rapid Thermal Annealing Temperature on Crystalline Quality

Gallium oxide (Ga2O3) is a semiconductor with a wide bandgap of ~5.0 eV and large breakdown voltages (>8 MV·cm−1). Among the crystal phases of Ga2O3, the monoclinic β-Ga2O3 is well known to be suitable for many device applications because of its chemical and thermal stability. The crystalline quality of polycrystalline β-Ga2O3 films on c-plane sapphire substrates was studied by rapid thermal annealing (RTA) following magnetron sputtering deposition at room temperature. Polycrystalline β-Ga2O3 films are relatively simple to prepare; however, their crystalline quality needs enhancement. The β-phase was achieved at 900 °C with a crystallite size and d-spacing of 26.02 and 0.2350 nm, respectively, when a mixture of ε- and β-phases was observed at temperatures up to 800 °C. The strain was released in the annealed Ga2O3 films at 900 °C; however, the clear and uniform orientation was not perfect because of the increased oxygen vacancy in the film at that temperature. The improved polycrystalline β-Ga2O3 films with dominant (−402)-oriented crystals were obtained at 900 °C for 45 min under a N2 gas atmosphere.