The mobility edge since 1967

Publisher Website
Google Scholar
Abstract
A mobility edge is defined as the energy separating localised and non-localised states in the conduction or valence bands of a non-crystalline material, or the impurity band of a doped semiconductor. This review is limited to three-dimensional systems, since in one or two dimensions a mobility edge in this sense does not exist, because all states are localised. The author distinguishes between the properties of electrons in the conduction bands of non-crystalline semiconductors, notably hydrogenated amorphous silicon (a-Si-H), and those in a degenerate electron gas, such as that in amorphous Si-Nb alloys or impurity bands in doped crystalline semiconductors. In the former the use of a one-electron model is legitimate, but a consideration of the interaction with phonons is essential; even at the absolute zero of temperature this leads to a broadening of the mobility edge. The main purpose here is to review recent work on the effects of this interaction on the pre-exponential factor sigma 0 in the conductivity expressed as sigma = sigma 0exp(-(Ec-EF)/kBT) and the pre-exponential factor in the drift mobility. In the final section he also gives a brief review of some of the recent work on the effects of the electron-electron interaction in metallic systems and also spin-orbit scattering.