Optical studies of MOCVD-grown GaN-based ferromagnetic semiconductor epilayers and devices

Ga1–xMnxN epilayers and p‐i‐n device structures have been grown by metalorganic chemical vapor deposition. Optical studies were found to investigate the role of Mn concentration and the role of different co‐dopants to elucidate the origin of the room temperature ferromagnetism in Ga1–xMnxN epilayers. Increasing Mn concentration was found to significantly affect long‐range lattice ordering. This observation was supported by the existence of a disorder‐induced Raman mode at 300 cm–1 and local vibrational modes (LVMs) at 669 cm–1 that has been attributed to the formation of self‐compensating nitrogen. The E1(TO) phonon frequency was found to linearly increase with Mn composition, which is expressed by (558 + 2.7x) cm–1. The intensity and the linewidth of an absorption band near 1.5 eV was found to increase with Mn concentration, and is assigned to the e to t2 transition in the split 5T2 band of Mn3+. No absorption was detected in Si co‐doped Ga1–xMnxN. In this case, a significantly increased EPR signal of Mn2+ ions confirmed the trapping of electrons provided by the shallow Si donor and reduced the available states for ferromagnetic exchange. A change in the measured magnetization is observed under ultraviolet illumination, though the nature of this phenomenon is still not understood. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)