Time-dependent density functional study on the excitation spectrum of point defects in semiconductors

A common fingerprint of the electrically active point defects in semiconductors is the transition between their localized defect states upon excitation, which may result in characteristic absorption or photoluminescence spectrum. While density functional calculations have been very successful in exploring the ground-state properties like formation energies or hyperfine tensors the density functional theory (DFT), in principle, is not capable of providing reliable excitation spectrum. Time-dependent (TD)-DFT, however, addresses this issue which makes possible to study the properties of point defects associated with their excited states. In this paper, we apply the TD-DFT on two characteristic examples: the well-known nitrogen-vacancy defect in diamond and the less known divacancy in silicon carbide. The former defect is a leading candidate in solid state quantum bit applications where detailed knowledge about the excitation spectrum is extremely important. The excitation property of divacancy will be also studied and its relevance in different applications will be discussed. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim