Local structure, bonding, and electronic properties of covalent amorphous semiconductors

Abstract

Amorphous solids, as opposed to crystalline solids, have an atomic structure with no long-range periodicity. Since the quantum theory of solids was developed in the period before the importance of amorphous materials was evident, the symmetries resulting from periodicity were exploited to simplify the calculation of physical properties. This led to a rapid understanding of the general behavior of crystals, but also obscured both the fundamental reasons for this behavior and the greater range of properties which could be achieved in amorphous solids. Even after amorphous semiconductors were discovered and characterized, an inordinately large effort was expended into understanding the properties of those amorphous materials with simple crystalline analogues. It is the purpose of this paper to emphasize the new modes of behavior when the constraints imposed by long-range periodicity are removed.