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Title: Charge transport in vacuum-sublimed and zone-cast pentacene field-effect transistors
Author: Duffy, C. M.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2008
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Abstract:
This thesis is concerned with the study of pentacene, a polycyclic aromatic hydrocarbon semiconductor, which is an attractive candidate for organic thin-film transistors (OTFTs) due to its large field effect mobility and high molecular order. The nucleation behaviour of vacuum-sublimed pentacene films is studied for several SiO2 surface treatments and field-effect mobilities of up to 0.6cm2/Vs were reproducibly obtained on hexamethyldisilazane (HMDS)-modified SiO2. The trapping mechanism upon bias-stressing in such vacuum-sublimed pentacene TFTs was studied by Scanning Kelvin Probe Microscopy (SKPM), which provided clear evidence that, in very thin pentacene films with island morphology, bias-stressed induced charge trapping occurs primarily in the thin intergrain regions only an incomplete charge accumulation layer can be formed and high gate voltages are required to charge portions of the film that are electrically not connected with the rest of the film at lower gate voltages. Alignment of the pentacene molecules was accomplished by zone-casting from solution in an anhydrous chlorinated solvent. Grazing Incidence X-ray diffraction (GIXD) confirmed that the pentacene crystallites are oriented with the ab plane parallel to the sample substrate, and the films exhibit a pronounced in-plane anisotropy with the a-axis of the unit cell aligned preferentially close to the zone-casting direction. The surface of the underlying dielectric is critical to achieving uniform and reproducible film morphology and benzocyclobutene-resin (BCB) was found to be a suitable gate dielectric buffer layer.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.598670  DOI: Not available
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