纤锌矿ZnO：Cu体系空位缺陷的电磁特性理论研究

ZnO:Cu体系具有p型导电性并出现室温铁磁性,但是对于其磁性来源还颇有争议.用Cu掺杂ZnO晶体容易增加空位缺陷产生的几率,从而使ZnO:Cu体系产生磁性.因此,本文采用基于密度泛函理论的第一性原理平面波超软赝势法对ZnO:Cu及其本征空位缺陷体系进行了理论研究,分别计算分析了ZnO:Cu超晶胞中相对Cu为近邻、次近邻、远近邻位置锌空位和氧空位的出现后体系的晶格结构、形成能、能带结构、态密度以及磁矩，以便准确合理地对其电磁特性进行判定.结果表明，ZnO:Cu远近邻VZn容易形成且其费米能级附近态密度较无缺陷体系增大,导电性增强;而含VO的缺陷体系禁带远远增大且变为间接带隙半导体，其费米能级处的态密度几乎不变或微弱减小,导电性无增强.Cu近邻VZn和VO的引入会导致ZnO:Cu掺杂系统的磁性相几乎或完全消失,但较远VO的出现无法显著改变磁性,较远VZn的出现使体系磁性增强.因此,在实验过程中要实现ZnO:Cu掺杂体系的良好电磁特性,应尽量避免Cu近邻VZn和VO的出现,而有效利用远近邻锌空位缺陷.

Theoretical studies on electronic and magnetic properties of vacancy defects in wurtzite ZnO: Cu system

A p-type conductivity and ferromagnetism at room temperature of the ZnO: Cu system has been proved, but for the origin of magnetism is still controversial. It is believed that Cu doped ZnO crystals can easily increase the incidence of vacancy defects, which lead ZnO:Cu system to be magnetic. Therefore, the first-principles calculations of ultra-soft plane wave method based on Density Functional Theory (DFT) were performed to present the theoretical studies on ZnO:Cu and its intrinsic vacancy defect systems. To accurately understand the electro-magnetic properties of the intrinsic vacancy defect in ZnO:Cu system, the formation energies, band structures, densities of states and magnetic moments of the ZnO:Cu supercells with the vacancy defects VZn and VO sites in the nearest, next nearest, and far nearest neighbors relative to Cu site were calculated and analyzed, respectively. The results demonstrated that the ZnO: Cu with far nearest VZn is easy to form and its density of states near the Fermi level increases and the conductivity increases in comparison with the defect-free system. The bandgap of the system containing defects VO increased immensely and the system is transformed into indirect bandgap semiconductor, the density of states near Fermi level is almost the same, or weak, and unable to enhance its conductivity. The introduction of the nearest VZn and VO relative to Cu sites will lead to the quenching of the magnetic phase in ZnO: Cu doped system nearly or completely. However, the presence of further VO could not significantly change the magnetism, the presence of further VZn brings about magnetic enhancement. Therefore, the presences of the nearest VZn and VO relative to Cu sites should be avoided as far as possible in experimental process.