HIGH-FIELD TRANSPORT IN A-SIH

Electric field dependent DC-dark and transient photoconductivity data measured over a broad temperature (10 K less-than-or-equal-to T less-than-or-equal-to 300 K) and field regime (10(2) V/cm less-than-or-equal-to F less-than-or-equal-to 6 x 10(5) V/cm) in phosphorus and boron doped and intrinsic amorphous hydrogenated silicon (a-Si:H) are described. The data demonstrate the strong influence of the electric field on carrier propagation. Enhancements over 6 orders of magnitude in conductivity (sigma) are achieved for fields greater than 10(5) V/cm, which changes a-Si:H films from highly insulating to very conductive at low temperatures. The field dependence is described empirically by a power law sigma is similar to F(y) with y in the range 10 less-than-or-equal-to y less-than-or-equal-to 17. The enhancement and y depend on doping level with significant differences between electron and hole currents. These results are confirmed by transient photoconductivity experiments on intrinsic a-Si:H from which the carrier mobility (mu(D)) and the mutau-product are deduced. The drift mobility is enhanced by many orders of magnitude up to values Of mu(D) > 10(-2) cm2/Vs and is identified as parameter which dominates high field transport. The increase in mobility is comparable to the increase in conductivity and shows a time- and thickness dependence indicative of dispersive transport. The data is interpreted introducing a field-enhanced nearest neighbor hopping model which is governed by ballistic capture and field induced re-emission.