Structural compromise of the arsenic-terminated silicon (111) surface

The generalized-valence-bond method of electronic-structure calculation has been used to calculate equilibrium bond angles and bond lengths in a cluster representing the ideal Si(111)-(1×1)As surface. These are compared to equivalent parameters for the trisilylarsine molecule [(${\mathrm{SiH}}_3$ ${)}_3$As]. This molecule is assumed to represent an ‘‘ideal’’ structure for the ${\mathrm{Si}}_3$As unit since the Si atoms are not constrained to specific lattice positions. Nearest-neighbor distances between Si atoms in a Si(111) plane are 0.4 Å greater than the distance found in trisilylarsine. The structure of the Si(111)-(1×1)As surface can then be regarded as resulting from a compromise between ‘‘ideal’’ Si-As bond lengths and bond angles, given the constraints of the (111) surface atomic positions.