Transport properties of hydrogenated and chlorinated amorphous silicon Correlation with infrared transmission spectra

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Abstract
Electrical conductivity and infrared (i.r.) transmission measurements have been carried out on chlorinated and hydrogenated amorphous silicon films prepared by glow discharge. The hydrogen and chlorine concentrations have been measured by Rutherford back-scattering, nuclear activation, electron microprobe and i.r. data analysis. Upon decreasing the plasma power, a change of transport mechanism at 300 K was observed. In samples prepared at plasma powers of 10 W or above, the activation energy and the pre-exponential factor are found to be suggestive of transport of carriers in extended states of the conduction band. In samples prepared below 10 W, the temperature dependence of the dark conductivity around 300 K is characteristic of carrier transport through states localized in the band gap. These modifications in the transport mechanism are accompanied by changes in the hydrogen- and chlorine-related i.r. absorption bands: the SiH bands increase in intensity, while the SiCl2 bands decrease as the r.f. power increases. It is suggested that the SiCl2 species is mainly responsible for the band-gap density of states and the modification of the transport mechanism when the r.f. power is altered.