Power Law Behavior in Amorphous Si:H and Si:D Due to Hopping-Randomwalk of Electrons in Localized Band Tail States in Random Fractal Fluctuation

Electric field dependence of transit time in time-of-flight experiment has been investigated in four different a-Si:H films and three different a-Si:D films prepared in different conditions in order to identify the transport process of electrons and holes in a-Si:H and a-Si:D. It has been concluded that the dispersive transport of electrons and holes is due to hopping-randomwalk in localized band tail states in random fluctuation with fractal dimensions of 3.9. The hopping distance is in the range of 30 to 45 Å while the thermal activation energy is in the range of 0.12 to 0.19 eV for an electron and in 0.33 to 0.39 eV for a hole. Furthermore, we have found that the dispersion parameter is related to the exponent in the power law decay of photoluminescence. This shows that the power law decay of the photoluminescence is understood from the geminate recombination coupled with the hopping randomwalk in the random fractal fluctuation as shown by Ando et al. [phys. stat. sol. (b) 230, 15 (2002)].