A two-dimensional hole gas was found at the Si(111):Cl surface of an n-doped Si substrate in a recent experiment. This surface was investigated theoretically, using a self-consistent Poisson-Schrödinger model, and it was shown that this hole gas was not, contrary to a previously proposed explanation, intrinsic to the ideal Si(111):Cl surface. This finding was consistent with the ab initio electronic band structure. A theoretical examination was then made of a number of defects and impurities that might be expected to be present on this surface and find excess adsorbed chlorine atoms, acting as electronic acceptors, to be the most likely source of the observed hole gas. Further, simulations of scanning tunnelling microscopy images were performed that showed how these excess adsorbed chlorine defects should appear in experiments.

Origin of the Hole Gas at the Si(111):Cl Surface - Role of Surface Electronic Structure, Impurities and Defects. T.Blomquist, G.Kirczenow: Physical Review B, 2006, 73[19], 195303 (10pp)