稀土(Ce, Pr, Nd)掺杂和氧空位对ZnO磁光机理以及性能影响的研究

Nowadays, studies on magneto-optical properties of ZnO doped with rare earth (Ce, Pr, Nd) and oxygen vacancies have been reported experimentally in the literature. However, these studies only researched the random doping position without consideration for the unipolar structure of ZnO, and experimental study doping on the nano scale, the scale is greater. Moreover, restricted by experimental conditions, it is difficult to control the oxygen vacancies, magneto-optic mechanism and performance of doping system is difficult to grasp, magnetic mechanism is still controversial. First principles can be solve the problem of bottlenecks in the experiment reseach. In this study, we considered the unipolar structure of ZnO, and studied the magneto-optical properties of different doping contents and spatial ordering occupations of rare earth (Ce, Pr, Nd) doped and oxygen vacancies in ZnO. Therefore, we have set up supercell models for the same doping content、different spatial ordering occupations and the different doping contents、same spatial ordering occupation of rare earth (Ce, Pr, Nd) doped and oxygen vacancies in ZnO. We used Materials Studio software to calculate the geometry optimization, band structures, density of states, populations, electrons density difference and optical properties of all doping system based on the first-principle plane-wave GGA+U norm-conserving pseudopotential method in terms of the density functional theory (DFT). Comprehensive study the magneto-optic properties and mechanism of doping system. Through horizontal comparative screening, we expect to obtain the electron injection source material and high transmission rate emitting diode materials made with high stability, high Curie temperature and high electronic polarizability diluted magnetic semiconductor by the study on magneto-optical properties of doped system. The study will provide theoretical support for design and preparation of new functional materials.

目前，在实验上分别掺杂稀土(Ce,Pr,Nd)和氧空位对ZnO磁光性能影响的研究均有报道，但都只停留在研究随机掺杂上，未考虑ZnO的单极性结构。而且，实验研究掺杂体系都在纳米层面上，尺度较大。受实验条件限制，很难控制氧空位，掺杂体系磁光机理和性能也很难把握，磁性机理仍频有争议，第一性原理能够解决实验上的瓶颈问题。因此，本研究基于自旋密度泛函理论框架下的第一性原理平面波GGA+U模守恒赝势方法，分别构建稀土(Ce,Pr,Nd)掺杂和氧空位配比浓度相同，有序占位不同；有序占位相同，配比浓度不同的ZnO超胞模型，对所有体系进行几何结构优化、能带分布、态密度分布、布居值、差分电荷密度和光学性质的计算，系列研究掺杂体系的磁光性能和机理。通过横向比较筛选，预期获得稳定性高、居里温度高、电子极化率高的稀磁半导体电子注入源材料和透射率高的发光二极管材料。为设计和制备新型功能材料提供理论支撑。

由于本项目研究的所有掺杂体系磁性来源和机理均有争议，而且吸收光谱分布也有争议。为了解决此类问题，本项目采用密度泛函理论框架下的第一性原理平面波超软赝势+U的方法。第一，研究了Ce掺杂对ZnO磁光性能的影响，研究发现，随着Ce掺杂浓度的增加，铁磁性逐渐增强。Ce双掺ZnO体系沿a轴方向成键时，表现为反铁磁性；沿c轴方向成键时，表现为铁磁性，当Ce-Ce原子间距越增大，铁磁性越增强，可实现室温铁磁性。第二，研究了应变对Ce掺杂与点空位共存的ZnO光学性能和磁性的影响，在不同应变条件下，压应变使得Ce掺杂与O空位或Zn空位共存的ZnO体系的带隙变宽，静介电常数减小，复介电函数的虚部整体向高能级方向移动，吸收光谱蓝移；拉应变使得掺杂体系的带隙变窄，静介电常数增加，复介电函数的虚部整体向低能级方向移动，吸收光谱红移。第三，研究了Nd掺杂和点空位对ZnO磁光性能的影响，研究发现， Nd掺杂和Zn空位共存在ZnO中, 掺杂体系磁性来源主要由Nd掺杂和Zn空位形成复合体后的空穴载流子为媒介的双交换作用。Nd掺杂和O空位在ZnO中, 掺杂体系磁性没有增加; Nd掺杂和Zn空位在ZnO中, 磁矩提高, 稀磁半导体有利。Nd掺杂在ZnO中, 掺杂体系吸收光谱红移, 并且Nd双掺在ZnO中, 能够实现铁磁性和居里温度室温以上。第四，用第一性原理研究了Y/W/Li分别掺杂和点空位对ZnO磁光性能和机理的影响，解决了实验上磁光性能的认识均有争议的问题。这对设计和制备新型ZnO稀磁半导体有一定的理论指导作用。