Beta to Spinel Phase Transition of Magnesium Gallium Oxide Thin Films and Their Photoluminescence Properties

As a promising Ga2O3-based ultrawide bandgap semiconductor, beta (β) phase and spinel phase magnesium gallium oxide (MgGaO) with tunable bandgap larger than 4.8 eV has great potential in power electronics and deep ultraviolet optoelectronics. However, the role of Mg composition on the phase transition of MgGaO thin films from the β to spinel phase and their photoluminescence (PL) properties are still not explored. In this perspective, nine MgGaO samples with Mg atomic percent from 0 to 15.26% were grown by using oxygen plasma assisted molecular beam epitaxy. Bandgap tuning from 4.86 to 5.45 eV in MgGaO alloys was observed. The phase transition between β-MgGaO and spinel MgGa2O4 thin films was confirmed, and lattice parameters changing with Mg at. % were extracted by X-ray diffraction theta/2theta scans and in-plane reciprocal space mapping. Room temperature-, power-, and temperature-dependent PL properties of these MgGaO films were investigated, and the PL mechanisms were revealed.