Basic concepts of amorphous semiconductors

Research on large area electronic arrays of a-Si H devices started a few years later after the first field effect transistors were reported (Snell et al. 1981). These devices take advantage of the capability to deposit and process a-Si H over large areas. Applications include liquid crystal displays, optical scanners and radiation imagers. Present devices contain up to 10 individual elements and are presently used in handheld televisions and FAX machines. 

The disorder of the atomic structure is the main feature which distinguishes amorphous from crystalline materials. It is of particular significance in semiconductors, because the periodicity of the atomic structure is central to the theory of crystalline semiconductors. Bloch s theorem is a direct consequence of the periodicity and describes the electrons and holes by wavefunctions which are extended in space with quantum states defined by the momentum. The theory of lattice vibrations has a similar basis in the lattice symmetry. The absence of an ordered atomic structure in amorphous semiconductors necessitates a different theoretical approach. The description of these materials is developed instead from the chemical bonding between the atom, with emphasis on the short range bonding interactions rather than the long range order. 

The structural disorder influences the electronic properties in several different ways which are summarized in Fig. 1.1. The similarity of the 

The following brief survey of the properties of amorphous semiconductors is intended to provide an introduction to the subsequent more detailed discussion. 

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