Origin of shallow n-type doping in AlN

Abstract Achieving efficient n-type doping in AlN, a representative ultrawide bandgap (UWBG) semiconductor, remains a longstanding challenge that limits its application in high-power electronics and deep-ultraviolet optoelectronics. Conventional dopants in AlN often introduce deep levels or form compensating complexes, leading to low free-carrier concentrations. In this work, we combine first-principles defect calculations with a structural search method tailored to explore metastable configurations to systematically investigate donor-type defects in AlN. Our results reveal that the aluminum interstitial (Al i ) can exhibit shallow-donor behavior in specific metastable configurations that were previously overlooked. This discovery expands the understanding of n-type dopability in AlN, which can be extended to Al-rich AlGaN, and highlights the critical role of metastable defects in modulating electronic properties.