Band gap broadening and photoluminescence properties investigation in Ga₂O₃ polycrystal

Ga₂O₃ thin films were deposited on c-plane Al₂O₃ substrates by electron beam evaporation equipment. The effects of post anneal treatment on structure and optical properties of Ga₂O₃ were investigated. The X-ray diffraction (XRD) results of the as-grown and the annealed samples indicated the films consisted with the mix of \(\beta\)-phase polycrystalline and amorphous Ga₂O₃. The electron diffraction pattern confirmed the existence of the nanocrystal grains. AFM images revealed that the anneal treatment promoted the film crystallization. Both Ga₂O₃ fims exhibited high transparency from visible light to near infrared region. An obvious band gap broadening phenomenon was observed for the annealed sample comparing with the as-grown sample. The optical band gap of the annealed sample was as large as 5.68 eV, which was inconsistent with the bulk \(\beta\)-phase Ga₂O₃. Meanwhile, the center of ultraviolet emission peak blue shifted about 0.42 eV for the annealed samples. The mechanism of the band gap broadening effect and ultraviolet emission peak blue shift were discussed.