Energetics of the forms of hydrogen and hydrogen diffusion in realistic models of a-Si:H

Using ab initio density functional calculations we investigate the energetics of hydrogen in a-Si:H starting from basic supercells that contain 142 and 134 atoms and are completely free of defects. The study includes H atoms bonded to dangling bonds (dbs), bond centered (BH) hydrogen, molecular hydrogen, and interstitial hydrogen that turns out to be either in a floating bond configuration or at a tetrahedral site. The results are discussed with particular emphasis on H diffusion.