Growth and characterization of gallium oxide films grown with nitrogen by plasma-assisted molecular-beam epitaxy

Gallium oxide films were grown with nitrogen on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. Nitrogen and oxygen gases supplied simultaneously through one plasma source were used to grow gallium oxide films with nitrogen. All the films had monoclinic beta-Ga2O3 structure; however, their surface roughness increased with increasing nitrogen supply. The incorporation of nitrogen was confirmed by x-ray photoelectron spectroscopy. The average transmittance of the films was over 85% in the visible range and over 95% in the ultraviolet range. The as-deposited films had decreased bandgap energies from 4.92 eV to 4.35 eV, with increased nitrogen rate. That is, the bandgap energies of the gallium oxide films can be tuned simply by increasing nitrogen supply during their growth without any post-annealing process under nitrogen condition.