ABSTRACT
A material is classified as amorphous when it lacks the long-range structural order characteristic of a crystal, according to the usual definition. In this chapter the main structural quantities used for characterizing amorphous semiconductors were introduced. These quantities for respectively a crystal and a disordered/amorphous system were compared. Several structural quantities are useful for characterizing amorphous systems. One trivial is the local density that is, the number of atoms per volume unit. The number density is probably the simplest structural quantity that can be used to differentiate amorphous and crystalline phases. Another option for comparing the crystalline and the amorphous phases is by investigating the connectivity of the network formed by the chemically bonded atoms. The determination of the structure of amorphous semiconductors remains an unfinished quest. This is the case despite decades of dedicated efforts and is partly due to the lack of knowledge.
