Electronic structure of amorphous semiconductors

We review the bonding in a wide range of non-crystalline materials, such as the elemental and compound amorphous semiconductors, liquid semiconductors and, briefly, some oxide glasses and amorphous silicon dioxide. The review concentrates on the experimental determination of electronic structure from photoemission, optical spectra and core spectra and on its theoretical description, particularly using tight-binding methods. The review also describes the bonding at defects in amorphous semiconductors and in particular that of dopants and hydrogen in hydrogenated amorphous silicon (a-Si:H).