Importance of the sp2-like orbital formation for stabilizing surface local structures

Atomic configurations of GaAs (3 1 1)A, (1 1 1)A, and (1 1 0) surfaces were examined by using first-principles calculations to investigate the stabilization mechanism of surface structures. Although the bonds in the bulk state are sp3 hybridized bonds, it was found that the surface atoms form sp2-like bonds. This is because the total energy is not sensitive to the detailed atomic configurations at the surface and the energy level of the sp2 hybridized orbital is lower than that of the sp3 orbital. The sp2-like bond formation is rather general and important in stabilizing the surface structures.