Rare-Earth Doping and Co-Doping of GaN for Magnetic and Luminescent Applications

摘要

The main focus of this project is the study of Gadolinium doped Gallium Nitride. Calculations were carried out to elucidate the origin of the reported above room temperature ferro-magnetism in this system and the occurrence of much larger magnetic moments per Gd than the nominal moment of a Gd3+ ion. Defects are now thought to be responsible for the magnetism. While others proposed Ga vacancies were responsible, the present work showed that Ga vacancies in the triple negative charge state, which is the most likely charge state in semi-insulating samples, would not carry a magnetic moment. The neutral charge state held responsible for the magnetism by others was pointed out to be a very high energy of formation defect. Instead it is proposed that nitrogen and oxygen interstitials could play a crucial role in the magnetism. They show long-range ferromagnetic interactions, are likely defects caused by the implantation of Gd and/or growth disturbance and are relatively low energy defects. Furthermore, they are attracted toward Gd dopants. A recent proposal in literature about the role of Gd on N sites and pairs of Gd on adjacent Ga and N sites was evaluated and found to be unrealistic because of the hight energy of formation of Gd on N sites.