Investigation of Phase Transition and Ultrawide Band Gap Engineering in MgGaO Semiconductor Thin Films

Magnesium gallium oxide (MgGaO) ternary alloys with band gap energy larger than ∼5.0 eV can provide opportunities for optoelectronics in the deep ultraviolet spectral range and power electronics with extremely high critical field strength. It is important to grow high-quality MgGaO alloys with varied Mg compositions and understand their structural and optical properties. From this perspective, 20 MgGaO samples with Mg atomic percentages from 0 to 100% were grown by using oxygen plasma-assisted molecular beam epitaxy. Band gap tuning from 5.03 to 5.89 eV was achieved for the ternary alloys, and all samples had a transmittance of over ∼90% in the visible spectral range. The lattice structures were confirmed to transform from the β phase in Ga-rich materials to the β and rocksalt mixture phase in high-Ga high-Mg alloys and to the pure rocksalt phase in Mg-rich alloys. How lattice parameters change with the increase of Mg atom % and the epitaxy relationship between MgGaO films and c-sapphire substrates were revealed.