A comparative DFT study of electronic properties of 2H-, 4H-and 6H-SiC(0001) and SiC(000(1)over-bar) clean surfaces: significance of the surface Stark effect

The electric field, uniform within a slab, emerging due to Fermi level pinning at both sides of the slab, is analyzed using DFT simulations of SiC surface slabs of different thicknesses. It is shown that for thicker slabs the field is nonuniform and this fact is related to the surface state charge. Using the electron density and potential profiles, it is proved that for high-precision simulations it is necessary to take into account a sufficient number of SiC layers. We show that the use of 12 diatomic layers leads to satisfactory results. It is also demonstrated that the change of the opposite side slab termination, both by different types of atoms or by their location, can be used to adjust the electric field within the slab, creating a tool for simulation of surface properties, depending on the doping in the bulk of the semiconductor. Using these simulations, it was found that, depending on the electric field, the energy of the surface states changes in a different way than the energy of the bulk states. This criterion can be used to distinguish Shockley and Tamm surface states. The electronic properties, i.e. energy and type of surface states of the three clean surfaces: 2H-, 4H-, 6H-SiC(0001) and SiC(000 (1) over bar), are analyzed and compared using field-dependent DFT simulations.