Origins of optical absorption and emission lines in AlN

To aid the development of AlN-based optoelectronics, it is essential to identify the defects that cause unwanted light absorption and to minimize their impact. Using hybrid functional calculations, we investigate the role of native defects and their complexes with oxygen, a common impurity in AlN. We find that Al vacancies are the source of the absorption peak at 3.4 eV observed in irradiated samples and of the luminescence signals at 2.78 eV. The absorption peak at ∼4.0 eV and higher, and luminescence signals around 3.2 and 3.6 eV observed in AlN samples with high oxygen concentrations are attributed to complexes of Al vacancies and oxygen impurities. We also propose a transition involving Al and N vacancies and oxygen impurities that may be a cause of the absorption band peaked at 2.9 eV.