Solid-phase epitaxial crystallization of β-Ga₂O₃ thin film by KrF excimer laser irradiation from backside of NiO (111)-buffered α-Al₂O₃ (0001) substrate at room temperature

We have investigated the solid-phase epitaxial crystallization of β-Ga₂O₃ thin films on NiO (111) (3 nm thick)-buffered α-Al₂O₃ (0001) substrates prepared by pulsed KrF excimer laser irradiation onto amorphous Ga₂O₃ thin films from the backside of the substrate at room temperature. The results of x-ray diffraction, reflection high-energy electron diffraction, and transmission electron microscopy indicated that the solid-phase crystallization of the amorphous Ga₂O₃ thin film to epitaxial β-Ga₂O₃ film started from the film/substrate interface toward the film surface with an average growth rate of about 0.1 nm thickness per one pulse irradiation. The optical bandgap of the epitaxial β-Ga₂O₃ thin films (∼80 nm thick) was estimated to be 4.9 eV from the UV/Vis transmittance measurement.