Computational discovery of extreme-gap semiconductors

The magnitude of the band gap has been traditionally applied as a criterion to distinguish semiconductors from insulators; materials with gaps less than 3 eV are typically semiconductors, while wider-gap materials tend to be insulators. However, the development of ultra-wide-band-gap semiconductors such as AlGaN, diamond, BN, and Ga₂O₃ has challenged this gap-based criterion for materials classification and gave rise to questions such as how far the band gap of semiconductors can increase while maintaining delocalized carriers for conductivity and what is the widest band gap semiconductor. By applying high-throughput density functional theory calculation, we develop a materials discovery strategy to identify new extreme-gap semiconductors. We discover that materials composed of light elements, crystallized in simple, densely packed structures, and having s-orbital characteristics of conduction/valence bands have large band gap (> 7 eV) but light carrier effective mass (m_e^* < 0.7 m_e m_h^* < 2 m_e) that enable shallow dopants and high mobility and suppress the formation of polarons. We subsequently perform atomistic calculation to predict dopability and mobility of candidate materials. Our analysis uncovers several known compounds with gaps as wide as 11.3 eV that can host delocalized carriers such as rs-BeO and reveals that there is no practical upper limit to the band gap of semiconductors.