Dopants and defects in ultra-wide bandgap semiconductors

Ultra-wide bandgap semiconductors, with bandgaps greater than 3.5 eV, have immense potential in power-switching electronic applications and ultraviolet light emitters. But the development of these materials faces a number of challenges, many of which relate to controlling electrical conductivity. In this work, we review the major obstacles for a set of these materials (focusing on AlGaN, AlN, BN, Ga2O3, Al2O3, and diamond) including limitations in n- and p-type doping and the effects of impurities and native point defects. We present an in-depth discussion on ultra-wide-bandgap nitride and oxide semiconductors, which face several similar challenges, as well as diamond, which presents a more unique scenario. The biggest obstacle for these semiconductors is attaining bipolar electrical conductivity, which means achieving both n-type and p-type conductivity within the same material. Toward this end, we also discuss potential future research directions that may lead to the development of bipolar ultra-wide bandgap semiconductor devices.