The localization of electrons in amorphous semiconductors: A twenty-first century perspective

This review covers those consequences of the localization of electronic states that appear to be universal features embracing all amorphous semiconducting materials where the electron–lattice interaction can be neglected, such as hydrogenated amorphous silicon. Several experimental measurements of these features are described. The role of strong electron–lattice interactions in some amorphous semiconducting systems, such as many chalcogenide glasses, is also discussed. In these systems, the electron–lattice interaction is so strong that it more than offsets the coulomb repulsion needed to put two electrons in the same energy state. Some experimental consequences of these so-called negative-Ueff systems are described. In addition, some universal features of metastable excitations for systems with both weak and strong electron–lattice interactions are discussed in the light of some recent experimental results.