Influence of N2 and O2 annealing treatment on the optical bandgap of polycrystalline Ga2O3:Cu films

Cu-doped Ga2O3 thin films were deposited by electron beam evaporation with subsequent annealing at 1000 °C in N2 and O2 for 1 h. The influence of the annealing atmosphere on the crystal structure, surface morphology and optical properties of Ga2O3:Cu films was investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and transmittance and photoluminescence (PL) spectroscopy. The optical bandgap deduced from the absorption spectrum was greater for the O2 annealed than for N2 annealed samples. In both cases the bandgap was wider than for bulk β-Ga2O3. The grain size and surface roughness were sensitive to the annealing atmosphere. Results confirmed that the annealed samples were polycrystalline β-Ga2O3 with some amorphous phase. We hypothesize that annealing in oxygen led to recrystallization of the Ga2O3:Cu film. Annealing treatment improved the crystal quality of Ga2O3:Cu films and the PL intensity of the samples increased.