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HL: Fachverband Halbleiterphysik

HL 98: Electronic Structure Theory

HL 98.7: Vortrag

Freitag, 30. März 2012, 11:15–11:30, EW 202

A comparison of density functionals for the charge transfer level of the N defect in ZnO — •Sung Sakong, Peter Kratzer, and Johann Gutjahr — Fakultät für Physik and Center for Nanointegration (CeNIDE), Universität Duisburg-Essen, Duisburg, Germany

Electronic structure of impurity states in semiconducting materials is a very popular research field in both science and industry. However, the most frequently employed density functional theory (DFT) method has a significant problem to reproduce the experimentally measured band gap. As a consequence, recently hybrid functionals are introduced to remedy the underestimated band gap.

We present a comparison of defect calculations between generalized-gradient-approximation (GGA-PBE) and hybrid functionals (HSE and PBE0) for the experimentally well characterized N impurity in ZnO [AIP Advances 1, 022105 (2011)]. In addition, we test also empirical correction schemes with +U and non-local potential [PRB 77, 241201 (2008)] methods on top of the GGA functional. By referring all energy levels to the vacuum level of the corresponding method, we are able to compare the results. From the calculations, we notice that the charge transfer level (0/−) of N defects on the O site goes deeper into the gap in the methods that give a larger band gap, in good accordance with experiment and previous calculations [Appl. Phys. Lett. 95, 252105 (2009)]. Moreover, we find the absolute positions of the charge transfer levels with respect to the vacuum levels to be less dependent on the functionals than the band edges, because the charge states are determined from the more robust DFT total energies.