THERMOPOWER AND CONDUCTIVITY ACTIVATION-ENERGIES IN HYDROGENATED AMORPHOUS-SILICON - COMMENT

In a recent Brief Report [Phys. Rev. B 54, 7630 (1996)] Dyalsingh and Kakalios compared activation energies of transport data for doped a-Si :H. They confirmed once more that the activation energy of the de cond uctivity is larger by a tenth of an eV than the activation energy of t he thermoelectric power. In addition, the activation energy of the sho rt-circuit current in the presence of a thermal gradient for the same samples is examined. The authors found that this latter activation ene rgy coincides exactly with the activation energy of the de conductivit y and that also the absolute values of both conductivities are practic ally identical. They conclude that this latter finding is a strong ind ication for the presence of long-ranged potential and/or compositional disorder. In this paper we show that the latter result simply follows from Ohm's law and, therefore, gives no support to any specific trans port model.