ELECTRON AND HOLE TRANSPORT IN STABILIZED A-SE FOR X-RAY IMAGING
Date
1997-12
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ORCID
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Degree Level
Masters
Abstract
Time-of-flight (TOF) transient photoconductivity measurements were carried out on thermally evaporated, vacuum deposited selenium alloy photoconductor films, known as stabilized amorphous selenium (a-Se, nominal composition a-Se:0.2-0.5%As, 20ppm Cl), of various thicknesses. This study utilizes three different analytical methods to evaluate the transit time and drift mobility of the charge carrier. This work also investigate the effect of three different top contacts, gold, nickel and platinum, on the electronic properties of the photoreceptor. It is concluded that the contact type has no significant effect on the behavior of the photogenerated electron and hole pairs.
TOF measurements were also used on several stabilized a-Se samples to determine the dominant factor in charge carrier dispersion mechanism. Dispersion appears to increase linearly with an increase in the collected charge, due to coulombic repulsion of the carriers. However, if the effect of coulombic dispersion is eliminated, the dominant factor is concluded to be the multiple trapping of the carriers in transit. This finding is important for x-ray imaging, since it defines the process which controls the speed and resolution of the device. Finally the TOF measurements were used to evaluate the effect of bulk space charge build up in the photoreceptor due to charge injection by electrodes and/or repetitive photoexcitation of the sample. No net bulk space charge build-up was observed up to — 10 seconds for all the three contacts investigated.
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Degree
Master of Science (M.Sc.)
Department
Electrical Engineering