Optical Spectroscopy Study on β-Ga2O3

Undoped β-Ga2O3 single crystals were grown by the floating zone technique under different conditions, and subsequently annealed in O2. Excitation and luminescence measurements were correlated with optical absorption, Hall- and electron-paramagnetic resonance measurements. It is shown, that the UV luminescence does not have an intrinsic nature, as stated by other authors. UV and blue luminescence are related to the concentration of oxygen vacancies, and thus to the electrical conductivity. They are assigned to donor-acceptor transitions. On the contrary, a green luminescence was observed after band-to-band excitation, and it is attributed to self-trapped or bound excitons.