氧空位浓度对ZnO电子结构和吸收光谱影响的研究

First-principle study of the effects of oxygen vacancy on the electronic structure and the absorption spectrum of ZnO

目前,氧空位对ZnO形成杂质能级的研究结果存在相反的结论,深杂质能级和浅杂质能级两种实验结果均有文献报道,并且,在实验中高温加热的条件下,氧空位体系ZnO中导带自由电子增加的来源认识不足.为了解决此问题,本文采用密度泛函理论框架下的第一性原理平面波超软赝势方法,建立了纯的与两种不同氧空位浓度ZnO超胞模型,分别对模型进行了几何结构优化、态密度分布、能带分布、布居值和差分电荷密度的计算.结果表明,氧空位浓度越大,系统能量越上升、稳定性越下降、形成能越高、氧空位越难、导带越向低能方向移动、电子跃迁宽度越减小、吸收光谱越红移.这对设计制备新型氧空位ZnO体系光学器件有一定的理论指导作用.

Nowadays, the studies of the influence of oxygen vacancy on forming impurity level of ZnO have obtained contrary conclusions. The experimental results about both the deep impurity level and the shallow impurity level are reported.However, under the high temperature heating condition, the origin of free electron increasing in conduction band of ZnO with oxygen vacancy is not sufficiently understood. To slove this problem, according to the first-principles plane-wave ultrasoft pseudopotential of the density functional theory, we set up the models for a pure ZnO cell and two different oxygen vacancy concentration supercells of ZnO, and perform the geometrical optimization for three models. The density of state, band structure, population and differential electron density are also calculated. Calculation results indicate that with the increase of oxygen vacancy concentration, the total energy increases and the formation energy will be greater. It makes the stability decline and the oxygen vacancy harder. Meanwhile, its conduction band minimum shifts toward low energy, the electron transition width decreases, and the absorption spectrum is red-shifted. It shows that these results may be helpful for the future experimental design and also for the preparation of optical device with oxygen vacancy of ZnO.