中文摘要：

采用基于密度泛函理论的广义梯度近似平面波赝势方法,探究四种ZnO-Σ7（1230）孪晶界中VZn-NO-H复合体的电子结构和p型导电机理.计算结果表明,在ZnO-Σ7（1230）孪晶界中,N掺杂后会与锌空位（VZn）、氢填隙（Hi）等点缺陷结合,进而形成VZn-NO-H复合体,并出现在孪晶中的晶格应变集中区.此外,四种孪晶界中孪晶GB7a有利于VZn-NO-H离化能降低,从而使其表现出浅受主特征.分析显示特殊的孪晶结构导致了氮替位（NO）与近邻的O原子间距离缩短,阴离子之间发生相互作用,导致禁带中的空带能级下降,降低了电子跃迁所需能量.这一结果也说明GB7a孪晶界中的VZn-NO-H可能成为N掺杂ZnO材料的p型导电的来源之一.

英文摘要：

The origin of the p-type conductivity in N-doped ZnO has been a controversial issue for years, since isolated N substituted for O site（NO） was found to have high ionization energy. A recent experiment demonstrates that the p-type conductivity is attributed to the VZn-NO-H shallow acceptor complex. However, besides the complex, there are many other defects in Zn O, such as twin grain boundaries. They are commonly two-dimensional defects, and inevitably affect the p-type conductivity of the complex. By applying first principle calculations, we present the electronic structures and p-type conductivity of ZnO Σ7（1230） twin grain boundaries containing VZn-NO-H complexes. Four types of Σ7twin grain boundaries are investigated, and the VZn-NO-H complex is found to have a tendency to appearing in the stress raisers of the twin grain boundaries. The lowest formation energy under Zn-rich condition is only 0.52 eV for the complex in GB7 a, a type of Σ7 twin grain boundary with anion-anion bonds, while the value is 3.25 eV for the complex in bulk ZnO. For the ionization energy, the complex in GB7 a is more easily ionized, and has a value of 0.38 eV,compared with 0.67 eV in bulk ZnO. The result of density of states shows that the electron transition is dominated by the empty defect levels in forbidden band, which are occupied by O 2p and N 2p orbital. Further analysis indicates that the special structure of GB7 a shortens the distances between NOand its neighbor O atoms, and the shortest N—O bond is only 2.38 A, which also means a strong orbital hybridization between O and N. As a result, the energy level splitting is enhanced, and the empty energy level in the forbidden band is shifted down to valence band maximum. So, GB7 a can favor the ionization in VZn-NO-H complex. Although GB7 a is a special case of the twin grain boundaries, the result also gives us a new idea to understand the origin of p-type conductivity in N-doped ZnO.