Deep recombination centers in a-Si:H

The nature of the deep recombination centers in a-Si:H is still a matter of considerable uncertainty. We present results here of transient ESR arising from dangling bonds in doped and undoped material at temperatures, defect levels and/or excitation energies for which direct band edge recombination is negligible. The efficiency for spin creation by sub- and near-band edge light is determined in the linear response regime in doped samples and is found to be of order unity. Thus, almost all recombination proceeds via a dangling bond, directly for sub-gap excitation or by a Shockley-Read mechanism for band edge excitation. The rate-limiting process for recombination is capture by neutral dangling bonds, D0, of electrons in undoped and n-type samples and of holes in p-type material.