Search

Abstract: The temperature dependences of the conductivity have been analyzed for a number of disordered materials (amorphous compounds, glasses, polycrystalline and pressed composite materials, etc.). It is shown that these dependences are usually described by the inverse Arrhenius law for nonpolar semiconductors and by the power law for polar materials. A model is proposed within which the universality of these laws for the conductivity is explained by the exponential form of the density of states near the Fermi level or in the range of the allowed band tails. This form of density-of-state function is observed for a large number of disordered materials with different nature. In the framework of the model, the conductivity obeys the inverse Arrhenius law upon one-phonon electron transitions between states and the power law upon multiphonon transitions. The corollaries following from the model proposed are considered.

The conductivity of C60 films in the temperature range of 100-300 K is determined by the jumps over localized states in the energy region of 1.5 - 2.0 eV. At T > 350 K the activation energy of conductivity is determined by the laws of charge transfer over delocalized states. At T > 350 K the optical width of the forbidden band coincides with the mobility edge.