中文摘要：

当Cr掺杂ZnO的摩尔数为0.0313-0.0625的范围内,掺杂体系的最小光学带隙宽度和吸收光谱分布随Cr掺杂浓度的变化出现了两类相反的实验结果。为了解决本问题,采用密度泛函理论（DFT）框架下的广义梯度近似（GGA＋U）平面波超软赝势方法,用PBE泛函的计算方案来描述电子间的交换关联能,对未掺杂ZnO和3种不同浓度Cr掺杂ZnO超胞模型进行了能带结构、态密度、差分电荷密度、布居值以及吸收光谱的计算。结果表明,当Cr掺杂摩尔数为0.0313-0.0625的范围内,随着Cr掺杂量增加,掺杂体系的晶格常数和体积增大,总能量和形成能减小,结构更稳定,掺杂更容易,最小光学带隙宽度增大,吸收光谱显著蓝移。计算结果与实验结果相一致,并合理解释了存在的问题。这对制备Cr掺杂ZnO中实现短波长光学器件有一定的理论指导作用。

英文摘要：

The studies of absorption spectra of Cr-doped ZnO have presented two contradictory experimental results,which are the red shift and blue shift on the optical bandgap and absorption spectra when the mole fraction of Cr increases in a range from 0.0313 to 0.0625.To solve this contradiction,based on the first-principles plane-wave pseudopotential of the spin-polarized density functional theory（DFT）,we set up four models for Zn1-xCrxO（x=0,0.0313,0.0417,0.0625）to calculate the band structure,density of state,difference charge density,population and absorption spectra using the method of generalized gradient approximation（GGA＋U）.The calculation results indicate that with the increase of mole fraction of Cr in a range from 0.0313 to 0.0625,the lattice parameters and the volume of doping systems increases,the total energy decreases,the formation energy decreases,thereby the doping becomes easier,and the doping system becomes more stable.Meanwhile,the optical bandgap of the doping system becomes wider,which suggests that absorption spectra of Cr-doped ZnO systems would have a blue shift.The calculation results are consistent with the experimental data.And the contradiction of blue shift and red shift of Cr-doped ZnO systems has been explained reasonably.These results may contribute to improve the design and the preparation of short wavelength optical devices from Cr-doped ZnO.