Y掺杂ZnO最小光学带隙和吸收光谱的第一性原理研究

Optical bandgap and absorption spectra of Y doped ZnO studied by first-principle calculations

对于Y掺杂ZnO,当摩尔数在0.0313-0.0625之内,Y掺杂量越增加,吸收光谱发生红移和蓝移两种不同实验结果均有文献报道.本文使用Materials Studio软件下的CASTEP模块中密度泛函理论的第一性原理平面波模守恒(Norm conserving)赝势GGA+U的方法,构建了未掺杂纤锌矿ZnO单胞以及Y掺杂ZnO的Zn_(0.9687)Y_(0.0313)O超胞、Zn_(0.9583)Y_(0.0417)O超胞和Zn_(0.9375)Y_(0.0625)O超胞模型.对掺杂前后体系的能带结构、态密度、差分电荷密度、布居值以及吸收光谱进行了计算.计算结果表明:当Y掺杂摩尔数在0.0313-0.0625之内,Y掺杂量越增加,掺杂体系的晶格常数、体积、总能量越增大,掺杂体系越不稳定、形成能越增大、掺杂越难;掺杂体系中平行于和垂直于c轴的Y-O键布居值越减小、离子键越增强、共价键越减弱、键长越变长;掺杂体系的最小光学带隙越变宽、吸收光谱发生蓝移现象越明显.吸收光谱的计算结果与实验结果相符合,合理解释了吸收光谱红移、蓝移的争论.这对制备Y掺杂ZnO短波长光学器件能起到一定的理论指导作用.

The studies on absorption spectra of Y-doped ZnO have presented two distinctly different experimental results,which are the red shift and blue shift on the optical bandgap and absorption spectra when the mole fraction of impurity increases from 0.0313 to 0.0625.To solve this contradiction,the calculations in this paper are carried out by the CASTEP tool in the materials studio software based on the first-principal calculations of norm conserving pseudopotential of the density functional theory,and the geometric structures of ZnO,Zn_（0.9687）Y_（0.0313）O,Zn_（0.9583）Y_（0.0417）O and Zn_（0.9375）Y_（0.0625）O systems are constructed.By using the method of GGA＋U,we calculate the band structure,density of state,electron density difference,population,orbital charges and absorption spectrum.The results show that with the doping amount increasing from 0.0313 to 0.0625,both the lattice parameters and the volume of doping system increase：the higher the total energy of the doping system the higher the formation energy of the doping system is,thereby making doping difficult and the stability of the doping system lower Increasing Y-doping concentration weakens the covalent bond,strengthens the ionic bond;as Y doping concentration increases,the Mulliken bond populations and bond lengths of Y-O parallel and vertical to c-axis decrease for the doping system.Meanwhile,the more the Y doping content,the wider the optical bandgap of the doping system becomes and thus more significant the blue shift of absorption spectra of Y-doped ZnO systems will be.The calculation results of absorption spectra of Y-doped ZnO system are consistent with the experimental data.And the contradiction between blue shift and red shift of absorption spectra of Y-doped ZnO system is explained reasonably.These results may contribute to the improvement of the design and the preparation of short wavelength optical devices from Y-doped ZnO.