Effect of carrier-carrier interactions on some transport properties in disordered semiconductors

Interactions between electrons are likely to play an important role in certain transport properties of disordered semiconductors, particularly where these properties depend on electrons in localized states. A working classification of these interactions into intra-site interactions, inter-site interactions and polarization, is made. The first class is believed to affect primarily the transport properties o carriers around the mobility gap, by introducing two-electron wave functions into this region. The second class can introduce an activation energy into the d.c. hopping conductivity at very low temperatures, affect the thermo-electric power, and increase noticeably the a.c. hopping conductivity above a certain frequency. The third class may reduce the activation energy of the d.c. conductivity; a reduction to zero is theoretically possible. Instances where some of the above effects may have been observed are cited.