Structures and energetics for polar and nonpolar SiC surface relaxations

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Abstract
We have investigated the nature of relaxations and resultant stability gains for polar (both Si- and C-terminated) and nonpolar (equal concentration of Si and C) surfaces of zinc-blende (cubic) and wurtzite (hexagonal) surfaces of SiC, using the tight-binding atom-superposition and electron-delocalization band technique. The ideally truncated C surfaces of (111) and (100) β-SiC are predicted to exhibit larger inward displacements and stabilizations than the Si surfaces, which is in agreement with the semiempirical total-energy band calculations of Lee and Joannopoulos but not with the empirical potential-function prediction of Takai et al. The inward displacements on these surfaces have associated with them increased surface-atom–to–substrate σ-bonding stabilization and the destabilization of the dangling surface-state band on the (111) surfaces and of both dangling surface-state bands on the (100) surfaces. The Si- and C-terminated (100) surfaces are calculated to undergo dimerizations similar to those observed on the Si(100) and C(100) surfaces with σ-bond formation and some stabilizing π overlap of the remaining surface dangling orbitals.