Optical properties of the nitrogen vacancy in AlN epilayers

AlN epilayers grown by metalorganic chemical vapor deposition were implanted with cobalt ions and studied by deep UV photoluminescence (PL). A PL emission peak at 5.87 eV (at 10 K) was observed for the Co-implanted AlN epilayers, which was absent in as-grown AlN epilayers. Temperature dependence of the PL intensity of the 5.87 eV emission line revealed an ion-implantation induced defect with energy level of about 260 meV below the conduction band. The 5.87 eV emission line is believed due to a band-to-impurity transition involving the nitrogen vacancy (VN) in ion-implanted AlN. The experimentally determined energy level of the nitrogen vacancy is in reasonable agreement with the calculated value of 300 meV. From the band-to-impurity transition involving VN, we have deduced the energy band gap of AlN to be 6.13 eV, which is consistent with our previous result. Our results suggest that nitrogen vacancies in AlN cannot make any significant contribution to the n-type conductivity due to the large binding ener...