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 (XPS) 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 oxygen-gallium vacancy complexes (VO-VGa), respectively. No visible transitions assignable to Mg and Cu acceptor levels could be extracted.