First-principles calculations of structural, electrical, and optical properties of ultra-wide bandgap (Al$$_x$$Ga$$_{1-x}$$)$$_2$$O$$_3$$ alloys

Alloys between Ga2O3 and Al2O3 (AGO) present a rich material space exhibiting numerous structural phases with unique optoelectronic properties that make them attractive candidates as ultra-wide bandgap (UWBG) semiconductors for next-generation power devices. Here we review the properties of AGO, focusing on theoretical results on the thermodynamics of Al incorporation and its consequences on the electronic structure. We review predictions and progress in experimentally realizing these alloys, as well as how composition influences important optoelectronic variables such as the band gap, band offsets, transport properties, and n-type dopability. A number of these parameters, such as the breakdown field (related to the band gap) and electron mobility, are discussed in assessing AGO in terms of relevant power device figures of merit. Overall, the rapid progress and predicted properties highlight the promise of AGO as a model UWBG semiconductor platform with the potential to revolutionize power devices.