Photoreceptors xerographic process

Measurements such as illustrated in Fig. 16 are also widely used for system evaluation. By dividing the overall xerographic process into exposure, photoreceptor, and development subsystems, then describing each subsystem with an appropriate transfer function, the output image density can be related to the input density through a four-quadrant plot (Paxton, 1978 Pai and Melnyk, 1986). In such a manner, the effects of changes in the various subsystems on the output image density can be readily determined. 

Fig. 6.1 Schematic depiction of the xerographic process for a positively corona-charged single-layer photoreceptor.

In recent years, a less familiar technique has been found very useful as a nondestructive method of investigating transport properties of photoreceptors (these are used in nonimpact printers for electronically processed or stored information). The technique is called xerographic TOF (XTOF) and it can be conveniently employed in parallel with the conventional measurements for photoreceptor characterization. In this chapter, we will briefly consider both traditional and xerographic TOF. 

LeComber (1975) showed that by suitable doping, a-Si could be made n- or p-type. These properties, in conjunction with the fact that plasma-deposition processes are generally amendable to large areas, were such that much of the early interest in a-Si was directed to photovoltaic applications (Carlson and Wronski, 1976 Kuwano. 1986). It was quickly recognized, however, that the requirements for photovoltaic applications were, in many respects, similar to those for xerographic photoreceptors. 

The electrophotographic process is initiated by deposition of a uniform surface charge from the corona on the xerographic photoreceptor belt in the... 

Xerographic discharge, which is a highly space-charge-perturbed process, is therefore characterized by significant dispersion in the arrival times of photoinjected carriers. In some cases, the transit times of the slowest carriers are 10 times or more than the transit times of the fast carriers. However, the slowest carriers, too, must exit the TL before the photoreceptor reaches the development zone, typically 0.3-1.0 s after exposure. In practice, carrier mobilities that significantly exceed 10 cm /V-s are desirable. 

Not so in the xerographic photoreceptor. Recall that majority carriers generated near the surface in the exposure step must be free to migrate from the top to the bottom of the dielectric layer to enable imagewise photodischarge in the fraction of a second, available between exposure and development. While the time scale of the process does not require high mobility, deep traps for the majority carrier must be excluded from the bulk otherwise, residual potential and background will build up as the photoreceptor cycles. 

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