Surface relaxation and oxygen adsorption behavior of different SiC polytypes: a first-principles study

The surface relaxations and oxygen adsorptions on C-and Si-terminated 3C-SiC(111) and 2H/4H/6H-SiC(0001) surfaces are systematically studied using density functional theory (DFT) calculations. First, the general surface relaxation trends of different SiC surfaces are explained using the electrostatic interaction and the calculation results of spin density distributions. In the second part of the present work, the relations between adsorption energies and stacking sequence are studied. We find that the adsorption energies of bridge, hollow-3 and T4 configurations on Si-terminated SiC surfaces increase with the increasing of the real number T (I), which is a translation of the polytypic sequence and quantifies the amount of 'h' character of the surface and of the deeper layers, while the energies of the on-top configurations on Si-terminated SiC surfaces and of all configurations on the C-terminated SiC surface seem to depend only on the stacking orientation of the topmost layer and not on the subsequent ones.