The mobilityhyphen;lifetime products of electrons and holes lsqb;(mgr;tgr;)eand (mgr;tgr;)hrsqb; in undoped hydrogenated amorphous silicon samples have been studied by photoconductivity and ambipolar diffusion length measurements. The density of dangling bondsNdin the samples is changed over a range of 3times;1015ndash;2times;1018cmminus;3by annealing at high temperatures.Ndand the Urbach tail slopeEovhave been determined by the constant photocurrent method. In addition, the optical gap, the activation energy of dark conductivity, and the exponent governing the intensity dependence of sgr;pchave been measured. The results show that there is a correlation betweenNdandEovwhich is consistent with equilibrium theory. (mgr;tgr;)eand (mgr;tgr;)hchange in quite different ways asNdincreases, namely, (mgr;tgr;)edecreases as a linear function of the inverse ofNd. However, (mgr;tgr;)hremains almost constant whenNdle;5times;1016cmminus;3, then decreases fast for higherNd. The asymmetric dependence of transport properties of electrons and holes onNdsuggests that for electrons recombination through dangling bond states is dominant; but, for holes, recombination mainly proceeds through deep band tail states, especially whenNdis relatively low.
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