Electronic structure calculations of defects in SiC and III-Nitrides
SiC and III-Nitride, such as GaN, AlN and their alloys, are the most promising materials for high-frequency power electronic and optoelectronic devices. The success of electronic device applications largely depends on the material quality and defect engineering. The latter implies the possibility to make good n- and p-type materials and to have control over the formation of deep level defects in order to manipulate the properties of the material to make it suitable for certain applications. The correlation between experiments and theoretical calculations and modeling is required for identification of defects and understanding their electronic structure. In addition, SiC is a very promising material to host solid state quantum bits realized by electron and nuclear spins of point defects [D.J. Christle et al. Nature Materials 14, 160 (2015); M. Widmann et al., Nature Materials 14, 164 (2015)] and to be used for sensing, such as vector magnetometry [M. Niethammer et al., Physical Review Applied 6, 034001 (2016)]. Identification and characterization of such point defects can mediate optimizing the qubit operations in SiC. This is a continuation of the on-going project, SNIC diary number SNIC 2015/1-429. In this project, the electronic structure, hyperfine interaction, electrical and optical properties of defects will be calculated within the supercell formalism. The parameters obtained from calculations will be compared with experimental data observed by electrical, optical and magnetic resonance techniques. In 2017, we continue our calculations of defects in SiC [K. Szász et al., Phys Rev. B 91 121201(R) (2015); A.L. Falk et al., Phys. Rev. Lett. 114, 247603 (2015); V. Ivády et al., Phys Rev. B 92, 115206 (2015) and Mater. Sci. Forum 858, 287 (2016); A. Gällström et al., Phys. Rev. B 92, 075207 (2015)], GaN and AlN. In SiC, we calculate the electronic structures of transition metal impurities as well as high-spin intrinsic defects. The high-spin intrinsic defects may act as quantum bits in SiC, and we will characterize them in depth. This is very time-consuming procedure since the common 4H-SiC and 6H-SiC polytypes contain two and three inequivalent substitutional sites, respectively. In GaN and AlN, we focus on the calculation of the hyperfine interaction of vacancies and complexes between the cation vacancies and shallow donors to combine with magnetic resonance experiments for the defect identification. We recently characterized nitrogen di-interstitial defects in AlN [Szállás et al., J. Appl. Phys. 116, 113702 (2014)] and will soon publish results on the cluster formation of nitrogen interstitial defects. We plan to extensively apply the accurate hybrid density functional methods within large supercells (typically 576 atoms). We need to use large supercells to efficiently model single defects. The cost of the hybrid functional calculation is about an order of magnitude larger compared to standard methods. Such calculations require large CPU time and, therefore, we ask for 200000 CPU-core hours/month on Triolith at NSC in 2017.