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Electrical properties of amorphous selenium based photoconductive devices for application in x-ray image detectors

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dc.contributor.advisorKasap, Safa O.en_US
dc.contributor.advisorJohanson, Robert E.en_US
dc.contributor.committeeMemberFaried, Sherif O.en_US
dc.contributor.committeeMemberDodds, David E.en_US
dc.contributor.committeeMemberNguyen, Ha H.en_US
dc.contributor.committeeMemberSargent, Colinen_US
dc.creatorBelev, Gueorgui Stoeven_US
dc.date.accessioned2007-02-13T10:22:26Zen_US
dc.date.accessioned2013-01-04T04:25:37Z
dc.date.available2008-02-14T08:00:00Zen_US
dc.date.available2013-01-04T04:25:37Z
dc.date.created2007-02en_US
dc.date.issued2007-02en_US
dc.date.submittedFebruary 2007en_US
dc.description.abstractIn the last 10-15 years there has been a renewed interest in amorphous Se (a-Se) and its alloys due to their application as photoconductor materials in the new fully digital direct conversion flat panel x-ray medical image detectors. For a number of reasons, the a-Se photoconductor layer in such x-ray detectors has to be operated at very high electric fields (up to 10 Volts per micron) and one of the most difficult problems related to such applications of a Se is the problem of the dark current (the current in the absence of any radiation) minimization in the photoconductor layer. This PhD work has been devoted to researching the possibilities for dark current minimization in a-Se x-ray photoconductors devices through a systematic study of the charge transport (carrier mobility and carrier lifetimes) and dark currents in single and multilayered a-Se devices as a function of alloying, doping, deposition condition and other fabrication factors. The results of the studies are extensively discussed in the thesis. We have proposed a new technological method for dark current reduction in single and multilayered a-Se based photoconductor for x-ray detector applications. The new technology is based on original experimental findings which demonstrate that both hole transport and the dark currents in a-Se films are a very strong function of the substrate temperature (Tsubstrate) during the film deposition process. We have shown that the new technique reduces the dark currents to approximately the same levels as achievable with the previously existing methods for dark current reduction. However, the new method is simpler to implement, and offers some potential advantages, especially in cases when a very high image resolution (20 cycles/mm) and/or fast pixel readout (more than 30 times per second) are needed. Using the new technology we have fabricated simple single and double (ni-like) photoconductor layers on prototype x-ray image detectors with CCD (Charge Coupled Device) readout circuits. Dark currents in the a-Se photoconductor layer were not a problem for detector operation at all tested electric fields. Compared to the currently available commercial systems for mammography, the prototype detectors have demonstrated an excellent imaging performance, in particular superior spatial resolution (20 cycles/mm). Thus, the newly proposed technology for dark current reduction has shown a potential for commercialization.en_US
dc.identifier.urihttp://hdl.handle.net/10388/etd-02132007-102226en_US
dc.language.isoen_USen_US
dc.subjectamorphous stateen_US
dc.subjectamorphous semiconductorsen_US
dc.subjectphotoconductivityen_US
dc.subjecta Seen_US
dc.subjectphotoconductorsen_US
dc.subjectmedical imagingen_US
dc.subjectradiation detectorsen_US
dc.subjecthigh resolutionen_US
dc.subjectdigital mammographyen_US
dc.subjectthick filmsen_US
dc.subjectexperimental studyen_US
dc.subjectelectron hole pairen_US
dc.subjectlifetimeen_US
dc.subjectlocalized statesen_US
dc.subjectcarrier lifetimeen_US
dc.subjecttrappingen_US
dc.subjectdrift mobilityen_US
dc.subjectcarrier mobilityen_US
dc.subjectcharge carrier trappingen_US
dc.subjectalloyingen_US
dc.subjectfabrication property relationen_US
dc.subjectarsenic additionsen_US
dc.subjectdopingen_US
dc.subjectchlorine additionsen_US
dc.subjectdeposition rateen_US
dc.subjectdeposition conditionsen_US
dc.subjectboat temperatureen_US
dc.subjectsubstrate temperatureen_US
dc.subjectannealingen_US
dc.subjecttime-of-flight methoden_US
dc.subjectdark currenten_US
dc.subjecttransients; transient curves; I-t curves; I-V curven_US
dc.subjectX-ray induced changes; dark current controlen_US
dc.subjectdark current reduction; multilayered structuresen_US
dc.subjectmetal electrodesen_US
dc.subjectblocking layersen_US
dc.subjectdouble layer structureen_US
dc.titleElectrical properties of amorphous selenium based photoconductive devices for application in x-ray image detectorsen_US
dc.type.genreThesisen_US
dc.type.materialtexten_US
thesis.degree.departmentElectrical Engineeringen_US
thesis.degree.disciplineElectrical Engineeringen_US
thesis.degree.grantorUniversity of Saskatchewanen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophy (Ph.D.)en_US

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