The Sillium Model
It is now two decades since a substantial number of solid state physicists switched their attention from crystals to amorphous solids, particularly amorphous semiconductors. From the outset the very structure of these materials was a contentious issue; it is still a matter on which quite divergent views are tenable. The continuous random model nevertheless persists as the generally accepted canonical model of the structure of a typical amorphous solid. Its first realisation for the tetrahedrally bonded Group IV semiconductors, took the form of the hand-built model of Polk (1971). Two other early models are shown in Figs 1 and 2. Although the characteristics of such hand-built models were surprisingly reproduceable and agreed quite well with experiment, it was always clear that such an arbitrary procedure was unsatisfactory. Since that time we have moved steadily towards more objective and realistic ways of constructing model structures, as illustrated in Fig. 3.
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