IMPURITY-DEFECT COMPLEXES AND DOPING MECHANISM IN A-SI-H

The most outstanding feature observed for dopants in hydrogenated amorphous silicon - a shift in the Fermi level accompanied by an increase in the charged-defect density - has previously been postulated to stem from the formation of substitutional-dopant-dangling-bond complexes. Using first-principles self-consistent pseudopotential calculations 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.