Effects of oxidation on surface band-gap states ina-Si:H

We use total-yield photoelectron spectroscopy in combination with the Kelvin probe to study changes in the work function and the distribution of occupied band-gap states upon oxidation of undoped and slightly boron-doped a-Si:H surfaces. We find that the work function changes rapidly upon activated oxygen exposure for both undoped and boron-doped surfaces corresponding to large (up to 0.3 eV) changes in the surface band bending. The Fermi energy becomes pinned 4.55 eV below the vacuum level by a large density (>1×${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$) of oxygen-induced surface band-gap states for activated oxygen exposures above 100×${10}^{\mathrm{-}6}$ Torr s. The origin of these oxygen-induced surface gap states is discussed.