Fakultät für Physik and Center for Nanointegration (CENIDE), Universität Duisburg-Essen, Lotharstrasse 1, 47057 Duisburg, Germany.
J Chem Phys. 2013 Jun 21;138(23):234702. doi: 10.1063/1.4810862.
Hybrid functionals and empirical correction schemes are compared to conventional semi-local density functional theory (DFT) calculations in order to assess the predictive power of these methods concerning the formation energy and the charge transfer level of impurities in the wide-gap semiconductor ZnO. While the generalized gradient approximation fails to describe the electronic structure of the N impurity in ZnO correctly, methods that widen the band gap of ZnO by introducing additional non-local potentials yield the formation energy and charge transfer level of the impurity in reasonable agreement with hybrid functional calculations. Summarizing the results obtained with different methods, we corroborate earlier findings that the formation of substitutional N impurities at the oxygen site in ZnO from N atoms is most likely slightly endothermic under oxygen-rich preparation conditions, and introduces a deep level more than 1 eV above the valence band edge of ZnO. Moreover, the comparison of methods elucidates subtle differences in the predicted electronic structure, e.g., concerning the orientation of unoccupied orbitals in the crystal field and the stability of the charged triplet state of the N impurity. Further experimental or theoretical analysis of these features could provide useful tests for validating the performance of DFT methods in their application to defects in wide-gap materials.
为了评估这些方法在预测宽禁带半导体 ZnO 中杂质的形成能和电荷转移能级方面的能力，我们将杂化泛函和经验修正方案与传统的半局部密度泛函理论（DFT）计算进行了比较。广义梯度近似（GGA）未能正确描述 ZnO 中 N 杂质的电子结构，而通过引入额外非局部势来拓宽 ZnO 带隙的方法，则可以得到与杂化泛函计算相当吻合的杂质形成能和电荷转移能级。通过对不同方法得到的结果进行总结，我们证实了之前的发现，即在富氧的制备条件下，N 原子取代 ZnO 中氧位的 N 杂质的形成很可能是稍微吸热的，并且会引入一个比 ZnO 价带边缘高出 1eV 以上的深能级。此外，方法的比较揭示了预测电子结构方面的细微差异，例如，关于晶体场中未占据轨道的取向和 N 杂质的带电三重态的稳定性。对这些特性的进一步实验或理论分析，可以为验证 DFT 方法在宽禁带材料缺陷应用中的性能提供有用的测试。
