Optical properties of intrinsic vacancy and interstitial defects in AlN

Aluminum nitride (AlN), a wide-band-gap semiconductor, is a key material for ultraviolet optoelectronics and emerging quantum technologies. However, its performance is significantly affected by intrinsic point defects that introduce deep and shallow levels within the bandgap. Here, we combine a hybrid quantum mechanical/molecular mechanical embedded cluster approach with direct comparison to photoluminescence and cathodoluminescence measurements to investigate the optical transition properties of the four most stable intrinsic point defects in AlN: aluminum vacancies, nitrogen vacancies, aluminum interstitials, and nitrogen interstitials. Calculated configuration-coordinate diagrams across all relevant charge states enable the assignment of experimentally observed optical bands to specific defect-related transitions. Our results highlight N vacancies as the dominant contributors to optical signals under most growth conditions. Although we find that Al vacancies are frequently associated with blue-to-UV optical transitions, their actual contribution remains uncertain due to the dependence of their formation on donor-rich environments. N split-interstitials also play a significant role depending on concentrations and growth conditions. This theoretical analysis, grounded firmly in suitable experimental compaisons, advances the understanding of defect-related optical properties in AlN and offers guidance for the design of optoelectronic and quantum devices.