AMORPHOUS CLUSTERS .1. ELECTRONIC-STRUCTURE OF SI CLUSTERS WITH N-DOPANTS, P-DOPANTS AND AS-DOPANTS

Amorphous impurity clusters of the type XSi20H28 with X = N, P and As have been studied using the well-known pseudopotential SCF Hartree-Fock method (and the HONDO Program). The local electronic density of states and charge density contours have been obtained. It is found that the covalent nature of the bonding in undoped silicon is altered by the presence of the dopants and both an ionic component and a shielding effect appear when N, P and As are substituted in the center of the amorphous cluster. Also, the local density of states in the neighborhood of a Si atom, nearest neighbor to the center of the cluster, indicates the presence of a new p-state in the band gap. There are quantitative differences in the electronic structure of the clusters as a function of the dopants. These results are analyzed in the light of the local changes and their relevance to the amorphous solid state properties.