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 degrees C in N-2 and O-2 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 O-2 annealed than for N-2 annealed samples. In both cases the bandgap was wider than for bulk beta-Ga2O3. The grain size and surface roughness were sensitive to the annealing atmosphere. Results confirmed that the annealed samples were polycrystalline beta-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. (C) 2013 Elsevier Ltd. All rights reserved.