Published online by Cambridge University Press: 26 February 2011
The Urbach energy E0 of undoped, Boron-, Nitrogen- and Phosphorus-doped a-Si:H deposited at 320°C from hydrogen-diluted silane mixtures has been measured by PDS. Its variations with impurity concentrations were related to those of the optical gap, of the defect density and of the width of the Raman TO peak. Taking into account the change in Hydrogen bonding in these materials, the physicochemical nature of the Valence Band Tail (VBT) states is discussed. A formal correlation between the dispersion of the Si-Si bond angle distribution and the width of the VBT is proposed within the Keating formalism.