Reaction pathways for intrinsic and extrinsic defect metastability in light-soaked hydrogenated amorphous silicon - the Staebler-Wronski effect

Reaction pathways are presented for photogeneration of defects in hydrogenated amorphous silicon (a-Si:H). Ab initio calculations performed on small molecular clusters demonstrate that proposed pathways are exothermic with reaction barriers of 0.25-0.40 eV. Pathways are based on optical absorption at defect precursors which include Si-H bonds in close proximity to: (i) strained Si-Si bonds, and/or (ii) Si-O-Si (or Si-(NH)-Si) groups. In each instance there is a hydrogen-bonding or weak electrostatic interaction involving the H-atom of the precursor Si-H group with its nearest neighbor. The demarcation between intrinsic and extrinsic pathways is estimated to be at defect concentrations of approximately 1019 cm-3.