ELECTRON AND HOLE TRANSPORT IN COMPENSATED AMORPHOUS-SILICON

A detailed investigation is presented of electron and hole drift mobilities, iic and in compensated a-Si over a wide range of the compensated doping ratio, Dc, (0-3 vol.p.p.m. to 5000 vol.p.p.m.). does not show anomalous dispersion and the interpretation of electron results leads to three distinct transport mechanisms. At low Dc, the multi-trapping model applies and μe is determined by the potential fluctuations associated with the randomly distributed ionized dopant sites. Experimental results are in good agreement with predicted fluctuation amplitudes. With increasing Dc, room-temperature electron transport changes to phonon- assisted hopping, at first near the bottom of the tail states and then through the donor states. /xh shows anomalous dispersion and is controlled by multi-trapping interaction with the tail states at all Dc. The dispersion parameter has been investigated as a function of D, suggesting that the tail-state distribution is unaffected by compensation. Finally, it is shown experimentally that the distribution of dopant sites is strongly dependent on the deposition parameters and that this can account for the fundamental disagreement in both experimental results and interpretation between the Xerox and Dundee work on compensated a-Si. © 1990 Taylor & Francis Ltd.