Markus R. Wagner

The monoclinic beta-phase of gallium oxide possesses an ultra-wide bandgap that surpasses other wide bandgap materials such as SiC and GaN, making it a promising candidate for power electronic device technologies. We investigate the first fundamental optical transitions in this material, which exhibit a strong directional dependence. To determine the energies and orientations of these transitions, temperature-dependent and angular resolved photoluminescence excitation spectroscopy is applied. We observe a distinct excitation channel located energetically between those of the first two optical transitions Γ1−1 and Γ1−2. While previous absorption edge and reflectance spectroscopy studies have assigned a transition in this spectral range to either the Γ1−1 or the Γ1−2 transition, our findings demonstrate no pronounced polarization dependence of this excitation channel within the (010) plane, an observation not reflected in calculations of the band-to-band transitions in β-Ga2O3.