关键词: 密度泛函理论/
ZnO/
孪晶界
English Abstract
Effect of ZnO twin grain boundary on p-type conductivity of VZn-NO-H complex:a GGA+U study
Wu Jing-Jing1,2,Tang Xin1,2,
Long Fei1,2,
Tang Bi-Yu3
1.Key Laboratory of New Processing Technology for Nonferrous Metal and Materials, Ministry of Education, Guilin University of Technology, Guilin 541004, China;
2.College of Materials Science and Engineering, Guilin University of Technology, Guilin 541004, China;
3.School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant No.11364009) and Guangxi Natural Science Foundation of China (Grant No.2014GXNSFFA118004).Received Date:24 January 2017
Accepted Date:04 May 2017
Published Online:05 July 2017
Abstract: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 ZnO, 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 ∑7 (1230) twin grain boundaries containing VZn-NO-H complexes. Four types of ∑7 twin 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 GB7a, a type of ∑7 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 GB7a 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 GB7a shortens the distances between NO and its neighbor O atoms, and the shortest N–O bond is only 2.38 Å, 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, GB7a can favor the ionization in VZn-NO-H complex. Although GB7a 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.
Keywords: density functional theory/
ZnO/
twin grain boundary
