Near-Surface Density of States in a-Si:H By Photoelectron Yield Spectroscopies.

Abstract

ABSTRACTThe density of occupied states was investigated in a number of intrinsic a-Si:H samples by means of photoelectron yield spectroscopy operated in the constant final state mode. Valence band edge, exponential tail and deep state distribution were analyzed and compared with the bulk density of states as determined by spectral dependence of photoconductivity. By evaporating Cs atoms on the clean surface the Fermi level position was progressively shifted toward the conduction band and the evolution of localized states was investigated. On the assumption that these near-surface states are paramagnetic centers with positive correlation energy, the results agree with the prediction of the “defect pool” model.