Available online 21 May 2003.
Abstract
We have proposed a structural model, the Formal Valence Shell (FVS) model, for amorphous semiconductors. This model is based on assumptions of non-doping and the domination of covalency. A concept of formal valence is used. The model states that the coordination number of each constituent atom is eight minus the formal valenve for the atom and that the average coordination number of a given composition is eight minus the average valence of the composition. The model is applicable to systems which contain non-metal (4 ⩽ N ⩽7) as well as metal atoms (1 ⩽ N ⩽3), where N is the valence or column number in the periodic table. The model therefore generalizes the conventional 8 - N rule which is applicable only to non-metal atoms. Sublattice assignments in ternaries are proposed. Given a set of constituent elements and their sublattice assignments, this model can provide coordination numbers, stoichiometric compositions, and trend of glass formation. I-V-VI ternaries are used for illustration, and other systems (binaries and ternaries) are addressed briefly. The calculated results generally agree with experimental data.
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