Electronic Structure and Ferromagnetism of Mn-doped GaN
Joongoo Kang and K. J. Chang
Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
Mn-doped GaN has currently attracted much attention because of the room-temperature ferromagnetism observed in this material. However, experimental data so far are quite controversial, reporting the Curie temperatures ranging from 10 to 940 K. Very recent experiments showed that Mn δ-doped GaN films have high hole carrier concentrations of about 1018 cm-3, which lead to the high Curie temperature and enhanced magnetization.
In this work, we study the electronic and magnetic properties of Mn-doped GaN and the origin of p-type conductance especially for Mn δ-doped films through first-principles pseudopotential calculations within the spin-density-functional theory. The nature of magnetic interactions between two Mn ions is investigated by varying the Mn-Mn distance and their orientation for both GaN bulk and GaN films. The ferromagnetic coupling in GaN bulk has a short-range nature, effective for Mn-Mn distances up to about 7 Å. The magnetic interactions in Mn-doped GaN films also favor a ferromagnetic ordering, with similar coupling strengths to those of bulk GaN. Analyzing the Mn d levels, we suggest that the d-d hybridization between Mn ions is the main reason for stabilizing the ferromagnetic state. The doping effect on ferromagnetism, and the energetics and ferromagnetism of Mn nanoclusters are also investigated. In Mn δ-doped GaN, we find that Ga vacancies are energetically more stable near the Mn layer than in the bulk region of GaN due to the charge transfer from the Mn to Ga vacancy. Our calculations suggest that Ga vacancies near the Mn δ-doped layer are likely to be the origin of p-type conductance observed in Mn δ-doped films.