STRUCTURAL BASIS FOR ELECTRONIC COHERENCE IN AMORPHOUS SI AND GE.

Abstract

There are good reasons to expect that polytope models are representative of local order in tetrahedrally bonded amorphous semiconductors. We have previously used polytope models, lattice structures in positively curved three-space, to compute certain features of the electronic and optical properties of amorphous Si. We show that the basic structural unit in polytope 240, the twisted boat type six-fold ring, is capable of more efficient local packing than the chair-type ring of the diamond structure. This local packing for amorphous Si and Ge implies preserved symmetries in the electronic structure and a basis for describing defects.