采用基于密度泛函理论的第一性原理赝势平面波方法研究了本征Mg2Si及钴(Co)掺杂Mg2Si体系的晶体结构、自旋态密度、磁性和光学性质。结果表明, Co替Mg(CoMg)缺陷的形成能为负, 可以形成稳定的缺陷。从自旋态密度可以看出, 本征Mg2Si为无磁性半导体; 向Mg2Si体系掺入Co后, 体系的磁矩由于Co3d态和Si3p态杂化(pd杂化)诱导产生, 且体系呈明显的半金属特性。超胞中Co的磁矩为0.53μB。从吸收光谱可以看出, Co掺杂Mg2Si的主吸收峰强度略小于本征Mg2Si, 但吸收跨度则明显大于本征Mg2Si。本征Mg2Si对于能量小于1.55eV(对应波长为800nm)的光子几乎不吸收, 而掺杂体系还存在着较大的吸收, 说明Co元素的掺杂显著地改善了Mg2Si对低能(红外)光子的吸收。计算结果为Mg2Si基自旋电子器件和光电子器件的设计和应用提供了理论依据。

The crystal structures, spin densities of states, magnetism and optical properties of intrinsic Mg2Si and Codoped Mg2Si were investigated using a firstprinciple planewave pseudopotential method based on the density functional theory. The results show that the defect formation energy is negative when Co atom occupies Mg site (CoMg) in the Mg2Si lattice. The calculated spin densities of states (SDOS) show that intrinsic Mg2Si belongs to the nonmagnetic semiconductor, however, Codoped Mg2Si with a magnetic moment of 0.53 per Codopant presents halfmetallic characteristic. The origin of the ferromagnetism in Codoped Mg2Si is found to be the hybridization of Co3d and Si2p orbits. The intensity of the main peak of Codoped Mg2Si is lightly less than that of intrinsic Mg2Si in the absorption spectrum, but the span of absorption is much larger than that of intrinsic Mg2Si. The infrared light absorption coefficient of Mg2Si is effectively improved due to Co doping.