Bonding Bands, Lone-Pair Bands, and Impurity States in Chalcogenide Semiconductors
The origin of electronic states in two classes of semiconductors is explored: (i) semiconductors containing group-VI elements in twofold coordination, and (ii) tetrahedral semiconductors. In the first case the valence band arises from the unshared electron pair (lone pair) of the group-VI atom. We examine the effects of compositional variation on the distribution of states in amorphous semiconductors. It is predicted that an Anderson transition will occur in the band of lone-pair states when a group-VI element is added to a tetrahedral amorphous semiconductor.