Electronic structure and transport in covalent amorphous semiconducting alloys

A brief review of the CFO model is given in which its principal features and what may be interpreted as its successes are listed. A few new results lending further support to features of the model are also reviewed. Upper and lower limits are given for the mobilities in the familiar regimes of propagation with occasional scattering and of phonon-assisted hopping between localized states, respectively. Mobilities in disordered materials frequently fall between these limits. Simple physical arguments are given which suggest that carrier motion in this intermediate regime takes place as Brownian motion. An estimate of the upper limit of the mobility for Brownian motion places it about equal to the lower limit for propagation. It is argued that the thermopower of carriers in this intermediate regime should be normal, whereas the Hall coefficient of holes should be negative. A summary of results of Johnson and the author for carrier kinetics in the CFO model is given. A calculation of the I-V characteristics at high field is briefly described.