空位缺陷及Mg替位对纤锌矿(Ga,Mn)N电子结构和磁光性能的影响

Effects of vacancy defect and Mg substitution on electronic structure,magnetic and optical properties of wurtzite structure (Ga,Mn)N

采用自旋密度泛函理论框架下的广义梯度近似(GGA+U)平面波超软赝势方法,构建了未掺杂纤锌矿GaN超胞、三种不同有序占位Mn双掺GaN,(Mn,Mg)共掺杂GaN以及存在空位缺陷的Mn掺杂GaN超胞模型,分别对所有模型的能带结构、电子态密度、能量以及光学性质进行了计算.计算结果表明:与纯的GaN相比,Mn掺杂GaN体系的体积略有增大,掺杂体系居里温度能够达到室温以上;随着双掺杂Mn-Mn间距的增大,体系总能量和形成能升高、稳定性下降、掺杂越难;(Mn,Mg)共掺杂并不能有效增大掺杂体系磁矩,也不能达到提高掺杂体系居里温度的作用;Ga空位缺陷和N空位缺陷的存在不利于Mn掺杂GaN形成稳定的铁磁有序.此外,Mn离子的掺入在费米能级附近引入自旋极化杂质带,正是由于费米能级附近自旋极化杂质带中不同电子态间的跃迁,介电函数虚部在0.6868eV附近、光吸收谱在1.25eV附近分别出现了一个较强的新峰.

Developing Ga N based dilute magnetic semiconductors by making use of the preparation techniques for Ga N materials, and combining the electrical and optical properties of existing Ga N electronic devices with magnetic property will enable various novel spintronic devices to be made. The key enabler for the wide application of dilute magnetic semiconductors is room temperature ferromagnetism. Many research groups have reported numerous samples of Ga N based dilute magnetic semiconductors with distinctively different magnetic properties. It may be argued that no consensus exists on the origin and control of ferromagnetism in these materials. There exists little work focusing on different doping modes for double-Mn doped Ga N, Ga N co-doped with Mn and non magnetic elements, and Mn doped Ga N with vacancy defects, although such a doping method can significantly modify the electronic structures, magnetic and optical properties of these materials. Therefore, it is meaningful to study the effects of these different doping techniques on the electronic structure, magnetic and optical properties of Mn doped Ga N so as to understand the magnetic exchange interaction in Mn doped Ga N and improve its physical properties. In the calculation in this paper, the generalized gradient approximation（GGA＋U） plane wave pseudopotential method under the framework of spin density functional theory is used. Models for the geometric structures of undoped wurtzite Ga N supercell, three different doping modes of double Mn doped Ga N,（Mn, Mg） co-doped Ga N, and Mn-doped Ga N with vacancy defects are constructed. The band structures, densities of states, energies and optical properties of these models are analyzed. The results show that the Curie temperature of the Mn doped Ga N system can reach above room temperature. Compared with that of pure Ga N, the volume of the Mn doped Ga N system increases slightly. It is also discovered that the total energy and formation energy of the doped system increase with the Mn-Mn distance increasing, thereby lowering the stability of the system and making doping more difficult. Analysis reveals that co-doping the Ga N with（Mn, Mg） can neither effectively increase the total magnetic moment of the doped system, nor improve the Curie temperature effect. The defects induced by Ga vacancies and N vacancies in the doped system hinder the stable ferromagnetic coupling from forming. In addition, the incorporation of Mn ions forms the spin polarized impurity band near the Fermi level. Due to the transitions between different electronic states in the spin polarized impurity band, the peak around 0.6868 e V in the imaginary part of the dielectric function and the peak near 1.25 e V in the optical absorption spectrum appear, respectively. This work offers a new insight into the understanding of the magnetic mechanisms and optical properties of Mn doped Ga N, and will be conducible to improving its physical properties.