Electronic structure calculations of defects in SiC and III-Nitrides
Abstract
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 [Widmann, Janzén, Son, Gali et al., Nature Materials AOP (2014). DOI:10.1038/nmat4145]. Idenitification 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 2013/1-331. 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 2014, we continue our calculations of defects in SiC [K. Szász et al., Journal of Applied Physics, 115 073705 (2014); A.L. Falk et al., Physical Review Letters, 112 187601 (2014); Theoretical unification of hybrid-DFT and DFT+U methods for the treatment of localized orbitals, V. Ivády et al., Physical Review B, 90 035146 (2014)], GaN and AlN. In SiC, we calculate the electronic structures of transition metal impurities as well as high-spin intrinsic defects and will continue our studies in 2014. Particularly, we will focus on the very accurate calculation of their electronic structure and charge transition levels in order to unambiguously identify the origin of transition metal related signals in different polytypes of SiC. 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 such as oxygen to combine with magnetic resonance experiments for the defect identification. We recently characterized nitrogen di-interstitial defects in AlN using density functional theory [Szállás et al., Journal of Applied Physics, 116 113702 (2014)].
We plan to extensively apply the accurate hybrid density functional methods within large supercells (typically 576 atoms). We need to use large supercells in order to avoid the dispersion of the defect bands in the gap and to use only the gamma-point in the calculations to find the degenerate states. 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 150000 CPU-core hours/month on Triolith at NSC in 2015.
