X-ray photoelectron spectroscopy and photoluminescence study of copper and magnesium doped beta-phase Ga2O3

Magnesium (Mg) doped, copper (Cu) doped, and Mg and Cu co-doped β-Ga2O3 thin film samples were grown on c-plane sapphire substrates using plasma-assisted molecular beam epitaxy. X-ray photoelectron spectroscopy analysis confirmed the doping concentrations. In addition, changes in the valence band density of states near the valence band maximum were revealed, while no Fermi-level shifts were observed in all doped samples, suggesting no electrical conductivity change compared to the undoped sample. Room-temperature photoluminescence (PL) characterization using an ArF laser of 193 nm excitation and subsequent PL peak deconvolution were performed. No near-band edge emissions were observed. The PL in each sample is dominated by optical transitions between the conduction band and self-trapped hole levels, and donor–acceptor pair transitions. These donors and acceptors originate from oxygen vacancies (VO) and gallium–oxygen vacancy complexes (VGa–VO), respectively. No visible transitions assignable to Mg and Cu acceptor levels could be extracted.