Arrhenius diagrams of conductivity when localized states are distributed within the gap

Abstract

This work achieves the putting into prominence of the incapability of Arrhenius diagrams of conductivity sigma (T), at thermal equilibrium, to determine the parameters of localized states. Simulations performed on exact models (free of simplifications) associated with (donor) states, uniformly distributed within bands of any width and position and compensated by band-spread acceptors, show behaviours very similar to those previously described for the related discrete level cases. The overall curve shapes are the same. Activation energies are well defined from extended linear parts of curves, but they are related to a (unique) level located within the band limits. The same behaviours, versus acceptor location, are observed when acceptors cease to be deep. It may be that only the important difference in the temperatures of the Meyer-Neldel converging points of the linear parts of curves dealing with discrete or distributed levels could be noted as an index of departure from this pattern. Therefore, it must be admitted that measuring sigma (T) allows no credible characterization of localized states.