Magnetism induced by Ga vacancy in rare earth R(R=Gd,Eu,Tm)doped GaN

In recent years, GaN doped with rare earth has attracted much attention due to its potential application in spintronic devices and optoelectronic devices. Based on the density functional theory, we investigate the magnetic moment, formation energy, and electronic structure in R (R= Gd, Eu, Tm) doped GaN semiconductors. We focus on the contribution of Ga vacancy to the magnetism, and calculate the formation energy of different Ga vacancies in the presence of Gd, Eu, or Tm dopants, and that of Gd, Eu, Tm dopants in native defects of Ga vacancy. The possible stable defect structures in GaN are given according to their formation energy. It is found that the Ga vacancies prefer to form cluster, and the formation energy of concentrated Ga vacancies is low compared to separated Ga vacancies. The 5d electrons of rare earth as well as 4f electrons have a larger contribution to the magnetism of GaN:R with Ga vacancy than without Ga vacancy. In addition, intermediate bands were observed in GaN:R with intrinsic defects, which possibly opens the potential application of R-doped semiconductors in the third generation high efficiency photovoltaic devices. (paper)