Effects of growth temperature on the valence, optical and magnetic properties of Mn-doped GaN films grown by metal organic chemical vapor deposition

Mn-doped GaN epitaxial films were grown at 900 °C, 930 °C, and 980 °C on sapphire substrates (0 0 0 1) by metal organic chemical vapor deposition. The valence of Mn ions in the GaN:Mn films was investigated by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. It is found that Mn ions exist at Ga substituting sites as Mn3+ in films grown at a relatively high temperature of 980 °C and as Mn2+ in films grown at a relatively low temperature of 900 °C. The Mn ions in the films grown at 930 °C show mixed valence. Photoluminescence measurements were performed. Fine structures in ultraviolet band are observed for each film. However, broad aquamarine luminescence band around 484 nm is pronounced only in spectra of the film grown at 900 °C, which is attributed to excess Ga in GaN. In addition, Mn-related zero phonon line (ZPL) at 1.414 eV and its phonon replicas were detected in the films grown at 930 °C and 980 °C. The ZPL and its replicas are assigned to the internal 5T2 → 5E transition of the neutral Mn3+ state. Magnetometry reveals that all Mn-doped GaN films show paramagnetic-like behaviors, not changed with growth temperature. These data indicate that temperature significantly influences the Mn valence and optical properties of Mn-doped GaN films.