Characterization of Polar Surface Effect on Silicon Carbide Defect States for Quantum Material Application Using DFT approach.

Silicon Carbide (SiC) polytypes, specifically 4H-SiC and 3C-SiC, emerge as promising host materials for defects, comparable to diamond, with the ability to house defect states serving as spin qubits. Ideally, it is desirable to position defects within a range of 10-30 Angstroms from the surface for effective spin readout. While extensive investigations into various bulk SiC defects have been conducted using both Density Functional Theory (DFT) and experimental methods, there needs to be more exploration into the impact of the SiC surface on these defects. We aim to characterize the defect states, namely the Divacancy (V_SiV_C) and Nitrogen-Vacancy (N_cV_Si)^-1, in the vicinity of 3C-SiC (111) and (001) surfaces as well as 4H-SiC (0001) surface. Using DFT methods, we calculate energy levels, zero phonon lines, and zero-field splitting of the defects as a function of the depth from the surface, surface orientation, and passivation. In general, surfaces exhibit surface states due to dangling bonds at the slab-vacuum interface, a phenomenon observed in materials such as SiC, Au, and Al. Furthermore, SiC, a naturally polar material, generates asymmetric slabs, resulting in spontaneous polarization across the slab. Thus, Silicon Carbide defects are influenced by both surface states and the internal electric field across the slab arising from the opposing dipole moments on the C- and Si-terminated surfaces. This study uses DFT methods to investigate the polar surface effect on silicon carbide defect states.