Growth, structure and carrier transport properties of Ga2O3 epitaxial film examined for transparent field-effect transistor

Growth conditions of heteroepitaxial thin films of tin-doped Ga2O3 were surveyed from the viewpoint of visible application to field-effect transistors (FETs). Films were deposited by pulsed laser deposition, and post-annealing was examined to improve film structures. Atomically flat surfaces were obtained for films grown on yttria-stabilized zirconia (111) plane and post-annealed at 1400 °C, but they were insulating. Conductive heteroepitaxial films applicable to FETs were obtained on α-Al2O3 (0001) at specific deposition conditions, i.e. substrate temperatures from 500 to 550 °C and oxygen pressures from 5 × 10− 4 to 1 × 10− 3 Pa. It was found that the resulting epitaxial films have a crystal structure different from that of β-Ga2O3. The crystal lattice for the films is determined to be orthorhombic with a large possibility of a higher-symmetry hexagonal or rhombohedral system. The films exhibited high transparency in the near infrared–deep ultraviolet region and had bandgap of ∼ 4.9 eV. The operation of top-gate MISFETs using the Ga2O3 film for the n channel was demonstrated.