Synthesis, phase composition, electronic and spectroscopic properties of cobalt-doped aluminum oxynitride

The article presents a comprehensive study of the synthesis, phase formation, electronic structure, and optical properties of cobalt-doped aluminum oxynitride Al₅O₆N (AlON) in the concentration range of 0.01–5 at%. The solubility limit of cobalt in AlON is found to be 0.1–0.2 at% compared to Al. No corundum is detected even at the lowest cobalt content (0.01 at%), but a low amount of AlN and Co or Co₄N is observed. Cobalt ions are incorporated into AlON with the typical oxidation state of Co²⁺ and form Co–O and Co–N bonds in a ratio of 92/8. The bandgap (E_g) and lattice parameters of AlON:Co are found to be in the range of 5.72–5.84 eV and 7.9411–7.9539 Å, respectively, and are influenced by the oxygen content. Pulsed cathodoluminescence spectra show five emission bands, with some attributed to (V_Al–O_N)-type defects. The luminescence intensity of AlON:Co decreases with higher contents of cobalt ions.