HIGH FIELD TRANSPORT IN a-Si:H

Abstract

Electric field dependent DC-dark and transient photoconductivity data measured over a broad temperature (10 K ≤T≤300 K ) and field regime (102 V/cm ≤F≤6×105 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 (σ) are achieved for fields greater than 105 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 a~Fy with y in the range 10≤y≤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 (μ D ) and the μτ-product are deduced. The drift mobility is enhanced by many orders of magnitude up to values of μ D >10−2 cm 2/ 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.