Coulomb effects and thermopower in elemental covalent amorphous semiconductors

It is shown that the Coulomb effects resulting in a single-occupancy of localized states in the vicinity of the chemical potential in the mobility gap yield a simple possibility to explain both the magnitude and the temperature insensitiveness of the thermoelectric power of amorphous Ge and Si in the phonon-assisted hopping regime observed at low temperatures.The main physical ideas of this work resulted from a collaboration with Drs. A.Aldea and L.Bányai (see ref. 28]). The present author acknowledges with pleasure their significant contribution to this work.