Beta to Spinel Phase Transition and Photoluminescence Properties of MgGaO Thin Films Grown by Molecular Beam Epitaxy

This study explores the phase transition behavior and photoluminescence (PL) characteristics of MgGaO thin films grown via plasma-assisted molecular beam epitaxy, with varying Mg atomic percentages ranging from 0 to 15.26%. Systematic investigation reveals distinct phase boundaries: MgGaO films exhibit pure β-phase at lower Mg concentrations (0-4.05%), a coexistence of β-phase and spinel phase at intermediate Mg levels (6.71-12.04%), and complete transition to pure spinel phase at higher Mg concentrations (13.31-15.26%). Structural analysis via X-ray diffraction confirms these transitions and identifies corresponding changes in lattice parameters. Comprehensive PL studies, encompassing room temperature measurements as well as power and temperature-dependent analyses, have revealed distinct emission spectra and mechanisms intrinsic to β-MgGaO and spinel MgGa₂O₄. These investigations have elucidated defect energy levels associated with various entities such as self-trapped holes (STH), deep donors from oxygen vacancies, deep acceptors involving Mg on Ga sites, and acceptor complexes formed with Ga and O, which are pivotal for advancing optoelectronic applications of these materials. This research enhances our understanding of MgGaO alloy phase evolution and provides insights for optimizing ultra-wide bandgap semiconductor devices.