Scher-Montrol theory

Typical photocurrent transients are shown in Fig. 6 for electrons and in Fig. 7 for holes. The shape of these curves is representative for all transients observed in the study and is characteristic of dispersive transport [64-68]. The carrier mobility p was determined from the inflection point in the double logarithmic plots (cf. Fig. 6b and Fig. 7b) [74]. TOF measurements were performed as a function of carrier type, applied field, and film thickness (Fig. 8). As can be seen from Fig. 8, the drift mobility is independent of L, demonstrating that the photocurrents are not range-limited but indeed reflect the drift of the carrier sheet across the entire sample. Both the independence of the mobility from L, and the fact that the slopes of the tangents used to determine the mobility (Fig. 6 and Fig. 7) do not add to -2 as predicted by the Scher-Montroll theory, indicate that the Scher-Montroll picture of dispersive transients does not adequately describe the transport in amorphous EHO-OPPE [69]. The dispersive nature of the transient is due to the high degree of disorder in the sample and its impact on car-... 

We see that the transit signal does not change appreciably with temperature. Also note that at the final stage (t > 1 ), the TOF signal exhibits a power-law decay and appears to be dispersive. According to the Scher-Montroll theory [33], in the case of the dispersive transport process, I(t) should exhibit power-law dependences rd-a) and 7 d+a) fpj. j respectively, where a is the disorder parameter. The... 

This chapter reviews theories proposed to describe charge transport in materials of potential relevance to xerography. The emphasis is on the disorder formalism, polaron arguments, and the Scher-Montroll formalism. These have been the most widely used during the past decade. For reviews, see Silinsh (1980), Movaghar (1987, 1991), Bassler (1993), Silinsh and Capek (1994), and Silinsh and Nespurek (1996). Experimental results are described in the following chapters. 

The transit time, which is clearly evident as a knee in Fig. 6, was measured as a function of applied bias V. The resulting drift mobility defined by = Lyvt, has a power-law field dependence, as shown in Fig. 7. In the theory of dispersive transport worked out by Scher and Montroll (1975) and others, the field dependence of the transit time is related to the time dependence of the current decay through a dispersion parameter a. In the theory, the current decay at short times (f < fx) the form and at long times (t > tx) the form t Similarly the transit time tx is proprotional to (L/Fy . Note that the data in Figs. 6 and 7 are consistent with these predictions of the theory with a = 0.51 at 160°K. 

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