Ionization energy of the oxygen donor in AlN

Oxygen is a ubiquitous impurity in AlN that influences its optical and electronic properties. A precise determination of its electronic levels is essential for device-specific material-engineering. In this study, we report on the experimental determination of the ionization energy of the substitutional oxygen donor O

_N in sputter-deposited and subsequently high-temperature annealed AlN templates using temperature-dependent and time-resolved cathodoluminescence spectroscopy. The slow component of the oxygen-related defect luminescence, associated with donor–acceptor pair recombination and with decay times of hundreds of nanoseconds, exhibits distinct thermal quenching at temperatures above 250 K. By fitting this temperature dependence with a model based on the thermal emission of electrons from the donor level, we extract an ionization energy E

_D = 371 ± 77 meV for the oxygen donor in AlN. This experimental value is in excellent agreement with theoretical predictions for the shallow substitutional O

_N donor and clearly distinct from calculated energies for the deeper oxygen DX center. This work provides an important experimental insight into this fundamental parameter in AlN.