Computational discovery of extreme-band-gap semiconductors.

The realization of ultra-wide-band-gap semiconductors has challenged the conventional distinction between semiconductors and insulators based solely on the magnitude of their band gap, and has raised fundamental questions about the limits of semiconducting behavior at extreme band gaps. We develop a computational discovery strategy based on first-principles electronic-structure and defect calculations to identify materials that combine ultra-wide band gaps with shallow dopants and mobile carriers. We first discuss our discovery of semiconducting rutile GeO₂ and its alloys with SnO₂, which have since attracted experimental interest for applications in power electronics and UV transparent conductors. Despite their ultra-wide gaps (3.6–4.7 eV), these materials exhibit shallow dopants, high mobilities, and high thermal conductivities. The n-type dopability has since been verified experimentally. Surprisingly, we find that alloy disorder in Sn-rich (Ge,Sn)O₂ has little impact on the electron mobility. We attribute this property to the insensitivity of the conduction-band edge with respect to Ge content in this composition range, which suppresses spatial fluctuations of the electron energies. We then apply this strategy to identify new semiconductors with band gaps exceeding that of AlN (6.2 eV) while retaining essential semiconducting properties such as shallow dopants and mobile charge carriers. We find that compounds composed of light elements in dense crystal structures can sustain shallow dopants, weak polaron binding, and mobile carriers even for gaps as wide as 9.5 eV. Our findings demonstrate that semiconducting behavior persists even at extreme band gaps, far beyond conventional upper bounds traditionally associated with semiconductor materials.