La掺杂量对ZnO光电性能影响的第一性原理研究

First-principles Study on the Effect of La Doping Concertration on the Photoelectric Properties of ZnO

采用密度泛函理论下的平面波超软赝势方法和杂化泛函理论下的模守恒赝势方法,分别计算了未掺杂ZnO和两种La掺杂浓度的ZnO模型,其中对较高La掺杂浓度的计算还设置了两种不同的掺杂位置。结构优化后,首先通过计算形成能、系统总能量和电荷布居值,对掺杂后体系的稳定性进行了分析;而后结合自旋基态能量与自旋电子态密度对掺杂体系的磁性状态进行了说明;最后通过计算得到的电子结构及吸收光谱讨论了La掺杂量对ZnO光电性能的影响。结果表明:随La掺杂量增加,ZnO体系稳定性有所降低;La掺杂ZnO无磁性,电子结构不会受到自旋能级分裂的影响;与纯ZnO相比,La掺杂ZnO的禁带宽度增大,吸收光谱蓝移,然而通过控制La浓度与掺杂方式可以有效增强La-5d与Zn-4s电子态的交换关联作用而减小ZnO的最小光学带隙,提高ZnO对可见光的吸收系数,使光生空穴-电子对有效分离的影响。

Base on first-principles with the density-functional theory and hybrid-functional theory, a pure ZnO model and two La doping ZnO models in different La concentrations were established, meanwhile two different doping sites of higher La doping concentration ZnO were calculated. After geometry optimization the author calculated total energy, population analysis, spin density of states, band structure and the absorption spectrum of all ZnO models. The results showd that La doped ZnO could be a stable structure, but more La atoms will decrease it. Near to Fermi level,there was no evident shifting of spin DOS and based on the total energies of different spin states it can judge that La doping ZnO is nonmagnetic. With La concentration increasing, the band gap of ZnO increases. However, controlling doping site could be a useful method to enhance the exchane-correlation between La-5d and Zn-4s y which raises the absorption coefficient of ZnO and it is helpful to separate electron-hole pair. All of those were beneficial to boost the photocatalytic activity of ZnO.