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

摘要

Electric field, uniform within the slab, emerging due to Fermi level pinningat its both sides is analyzed using DFT simulations of the SiC surface slabs ofdifferent thickness. It is shown that for thicker slab the field is nonuniformand this fact is related to the surface state charge. Using the electrondensity and potential profiles it is proved that for high precision simulationsit is necessary to take into account enough number of the Si-C layers. We showthat using 12 diatomic layers leads to satisfactory results. It is alsodemonstrated that the change of the opposite side slab termination, both bydifferent type of atoms or by their location, can be used to adjust electricfield within the slab, creating a tool for simulation of surface properties,depending on the doping in the bulk of semiconductor. Using these simulationsit was found that, depending on the electric field, the energy of the surfacestates changes in a different way than energy of the bulk states. Thiscriterion can be used to distinguish Shockley and Tamm surface states. Theelectronic properties, i.e. energy and type of surface states of the threeclean surfaces: 2H-, 4H-, 6H-SiC(0001), and SiC($000 \bar{1}$) are analyzed andcompared using field dependent DFT simulations.