COULOMB GAP, ITS CRITICAL-BEHAVIOR, AND THE METAL-INSULATOR-TRANSITION IN DOPED SEMICONDUCTORS

To measure a density of localized states in the vicinity of the Fermi level variable range hopping spectroscopy procedure has been establish ed. As a result the parabolic Coulomb gap has been discovered on a set of the series of doped and compensated semiconductors. The gap has a single- or multielectron origin for the case of strong localization wh en a compensation degree is close to unity or moderate correspondingly . All the gaps turned out to be collapsing in the critical point for t he metal-insulator transition. One can consider the transition as Coul omb gap collapsing phenomenon in a frame of the scaling theory describ ing it as a second order phase transition. The critical indices for a localization radius and for a metallic conductivity are nearly equal t o unity.