Impurity-defect complexes in hydrogenated amorphous silicon

The two most outstanding features observed for dopants in hydrogenated amorphous silicon (a-Si:H) -- a shift in the Fermi level accompanied by an increase in the defect density and an absence of degenerate doping -- have previously been postulated to stem from the formation of substitutional dopant-dangling bond complexes. Using first-principles self-consistent pseudopotential calculation in conjunction with a supercell model for the amorphous network and the ability of network relaxation from the first-principles results, we have studied the electronic and structural properties of substitutional fourfold-coordinated phosphorus and boron at the second neighbor position to a dangling bond defect. We demonstrate that such impurity-defect complexes can account for the general features observed experimentally in doped a-Si:H. 16 refs., 2 figs., 1 tab.