The generation of metastable neutral and charged defects in hydrogenated amorphous samples, by reactions which involved changes in H-atom bonding arrangements, was studied by applying ab initio calculations to small molecules. Reaction pathways were proposed for intrinsic processes which involved only Si and H atoms, as well as extrinsic processes which involved O and NH impurities as well. In photovoltaic devices, defect generation included the creation of neutral and charged defects and involved displacive rather than diffusive H motion. Positively charged defects were associated with over-coordinated H-, O- and N-atoms. In thin-film transistor devices, defect generation resulted from electron-trapping in anti-bonding orbitals of Si-H groups, and included the formation of neutral and negatively charged Si-atom dangling bonds.

A unified chemical bonding model for defect generation in a-Si:H H.Yang, G.Lucovsky: Japanese Journal of Applied Physics - 1, 1998, 37[3B], 1082-90