Theory of boron doping ina-Si:H

For a long time the rather low doping efficiency of B in $a$-Si:H has been explained by the argument that almost all of the B is incorporated into threefold coordinated sites and that B is inert or nondoping in this configuration. Using ab initio molecular dynamics, we have studied the energetics and electronic structure (doping) consequences of B incorporation into $a$-Si:H both with and without H passivation. Our results suggest that the conventional view is in error and that the low doping efficiency is primarily due to H passivation. These results are consistent with the low doping efficiency of B as well as NMR studies on the large electric-field gradients experienced by the B atoms and on NMR double-resonance studies of B-H neighboring distances.