It was shown that minimization of the number of broken bonds present at the surface and a π-like bonding between the broken bonds were keys to the understanding of Si surfaces. To fully exploit the above mechanisms, for both the π-bonding and elimination of broken bonds, the surface atoms had to rearrange themselves rather thoroughly - namely, the surface topology and the ring structure had to be altered. Based only upon topological considerations and simple counting of broken bonds, the minimization of the number of broken bonds showed why the 7 x 7 surface was terraced (consisted of intersecting steps), why these steps (as well as steps on the cleaved surface) formed only in certain crystallographic directions, why the terraces were triangular and not hexagonal, why the surface structure was symmetrical 7 x 7 (as opposed to, say 5 x 9), and the origin of the spatial scale of the 7 x 7 reconstruction. Of the reconstruction models proposed for the cleaved 2 x 1 surface, the π-bonding model led to the largest total-energy benefit, and only the π-bonding model provided a natural interpretation of the various spectroscopic data on this surface. It was shown that one of the most widely used ideas in the context of semiconductor reconstruction, that of buckling, was inappropriate for homopolar semiconductors. Buckling, however, provided a valid reconstruction mechanism for heteropolar surfaces such as GaAs(110). These conclusions were based upon total-energy and surface-band calculations using the self-consistent pseudopotential method.

Theory of Semiconductor Surface Reconstruction - Si(111)-7 x 7, Si(111)-2 x 1 and GaAs(110). K.C.Pandey: Physica B+C, 1983, 117-118[2], 761-6