Observation of buried phosphorus dopants near clean Si(100)-(2x1) surfaces with scanning tunneling microscopy

We have used scanning tunneling microscopy to identify individual phosphorus dopant atoms near the clean silicon (100)-(2x1) reconstructed surface. The charge-induced band-bending signature associated with the dopants shows up as an enhancement in both filled and empty states. This is consistent with the appearance of n-type dopants on compound semiconductor surfaces and passivated Si(100)-(2x1), even though this clean surface has antibonding surface bands that protrude into the gap. We observe dopants at different depths and see a strong dependence of the signature on the magnitude of the sample voltage. The positively charged dimer vacancies, which have been observed previously, appear as depressions in the filled states because they disrupt the surface bands.