Photoconductor materials

The abihty to accept and hold the electrostatic charge in the darkness. The photoconductive layer should support a surface charge density of approximately 0.5-2 x 10 C/cm. The charge also has to be uniformly distributed along the surface, otherwise nonuniformities can print out as spot defects. The appHed surface potential should be retained on the photoreceptor until the time when the latent electrostatic image is developed and transferred to paper or, if needed, to an intermediate belt or dmm. In other words, the "dark decay" or conductivity in the dark must be very low. The photoconductor materials must be insulators in the dark. 

Light detectors fall into two categories photoconductors and photodetectors. Photoconductors are devices whose resistance decreases upon exposure to light. Cadmium sulfide (CdS) and cadmium selenide (CdSe) are the most commonly used photoconductor materials in the visible spectrum. They are still mostly produced by sputtering but CVD is used increasingly (see Ch. 12, Sec. 4.0). 

Koch-Yee Law. Organic photoconductor materials for xerographic photoreceptors (Advanced Tutorial A2). IS and T s Non-Impact Printing Conference 12, San Antonio, Texas, October 27, 1996. 

The related metastable material ZnIn2S4, which has potential applications as a photoconductor material, was deposited using LP-MOCVD at 400 °C from the indium-zinc precursor [(Et)2In(S2CNEt2)Zn(Et)(S2CNEt2)].335... 

Figure 3. Schematic representation of the charge deposited on two photoconductor materials ZnO-binder dispersion (top) and amorphous selenium (bottom).

The basic architectures which have been proposed for image sensing using organic semiconductors couple a single transistor per cell OFET architecture with an organic photodiode (Fig. 7.3 (a)) [142] or a photoconductor material such as titanyl pthalocyaninie (Fig. 7.3 (b)) [143]. These architectures allow the creation of fully additive photodetector elements on essentially arbitrary... 

Thus the zinc blende structure semiconductors can be useful for intrinsic photoconductive detectors. Compounds such as InSb have been used as intrinsic photoconductors [4.20], as well as for photovoltaic detectors, but greater versatility of wavelength response is possible with the Hg j tCd Te alloy system. The Hgi j.Cd,Te alloys have received considerable development effort in recent years and are the most prominent intrinsic photoconductor materials they will be analyzed in this subsection. The development of Hg, Cd Te has concentrated almost entirely on n-type material since it provides high photoconductive gain however, p-type Hg, Cd,(Te crystals may be useful for intrinsic photoconductive detectors also [4.21]. 

Nearly all the development of Hg, Cd Te alloys as intrinsic photoconductor materials to date has involved the composition range 0.18 5 x 0.4, corresponding to cutoff wavelengths of 3 30 pm. Alloys of the xci 0.2 composition... 

The fully p-type crystals with po 10 cm are of little use as photoconductor material because of their relatively high carrier concentration. Properties of such crystals have been reported by Elliott and coworkers [4.54]. 

Since extrinsic silicon photoconductor material has high resistivity at cryogenic temperatures it can be used to form the substrate of an accumulation mode CCD as shown in Fig. 6.11. With an accumulation mode MIS structure the gates are biased so that majority carriers are stored and transferred down the insulator semiconductor interface. Local potential wells are formed under the gates however the dynamics of the charge transfer process will be very different from those for an inversion mode device since with an accumulation mode device the transverse electric fields will extend all the way to the back contact instead of being confined to the depletion region of an inversion mode structure. 

Amorphous selenium metal was originally used as the photoconductor (photo charge carrier generator) of the Carlson process in electrophotographic reprography. Because of its toxicity and difficulty of fabrication, selenium was then replaced by organic photoconductor materials (OPC). 

Fig.4.79. Spectral dependence of detectivity D for several photoconductor materials (after [4.55a])...

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