ELECTRONIC-PROPERTIES IN DISORDERED SOLIDS .3. HOPPING TRANSPORT MECHANISMS ASSOCIATED TO PAIR MODELS AND POLARON CONDUCTION

In two previous papers, we presented the general band scheme for amorphous semiconductors and the related transport phenomena. With an alternative way, two hopping models can be used in the case of high disorder: the pair model linked to hopping over the barrier of potential and the polaronic model. The first model leads to a frequency dependence sigma(omega) proportional to omega(s), where s is temperature dependent, contrary to the Austin-Mott law (tunnelling effect). The second model is independent of the band scheme and takes into account the carrier-lattice coupling: when the distortion tends to lower the energy of the carrier, a polaron is formed; in this case, we will describe the evolution of the d.c. conductivity, of the thermopower and of the alternative conductivity with temperature.