Theory of phosphorus doping in α-Si:H

For a long time the rather low doping efficiency of P and B in a-Si:H has been explained by the argument that almost all of both is incorporated into threefold-coordinated sites, and that both are inert or nondoping in this configuration. Recently, using ab initio molecular dynamics, the energetics and electronic structure (doping) consequences of B incorporation into a-Si:H both with and without H passivation were studied. This work showed that the conventional view was in error and that the low doping efficiency in B is primarily due to Pi passivation. In this paper we similarly study P incorporation on a-Si:H both with and without passivation. We obtain quantitative results on the energetics and electronic structure of P atoms in a-Si:H. In this case, the results do support the conventional view. Thus P and B act very differently in a-Si:H. However, we also find that the P-H complexes that passivate P in crystalline Si are not even metastable in a-Si:H.