Emission properties of Ga₂O₃ nano-flakes: effect of excitation density

In the quest of developing high performance electronic and optical devices and more cost effective fabrication processes of monoclinic β-Ga₂O₃, new growth techniques and fundamental electronic and optical properties of defects have to be explored. By heating of dissolved metallic Ga in HCl in a NH₃ and N₂ atmosphere, nano-flake films of monoclinic β-phase Ga₂O₃ were grown as confirmed by XRD. From optical measurements, we observe two strong emissions. A red band peaking at ~2.0 eV and a UV band at ~3.8 eV. The band at ~2.0 eV is attributed to donor-acceptor pair recombination where the donor and acceptor level is suggested to be related to V_O and nitrogen, respectively. By studying the dependence of the intensity of the UV band at 3.8 eV versus excitation density, a model is suggested. In the model, it is assumed that local potential fluctuations forming minima (maxima), where the carriers would be localized with a summarized band offset for conduction and valence band of 1 eV. The origin of the fluctuations is tentatively suggested to be related to micro-inclusions of different phases in the film.