Structure and H Bonding in Device Quality a-Si:H

A brief account is given of the applications of hydrogenated amorphous silicon, a-Si:H, to devices including photovoltaic cells. The role of impurities and defects in modifying device quality is given an historical perspective. Whilst the deliberate incorporation of dopants into the amorphous network promises further advances, the simplistic picture of H reducing free spin density is insufficient. To utilise fully the electronic properties of a-Si:H, a deeper understanding of the structure at the molecular level is required, especially those structures including H in close proximity which are unique to amorphous solids.