Graduate Thesis Or Dissertation
 

Alternating-current thin-film electroluminescent device optical excitation experiments

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/m613n114c

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  • This thesis investigates two methods of optical excitation of alternating-current thin-film electroluminescent (ACTFEL) devices. The two experimental methods investigated in this thesis are the photo-induced charge (PIQ) and luminescence (PIL), and the subthreshold-voltage induced transferred charge (VIQ) techniques. PIQ/PIL experiments utilize an above-bandgap laser pulse to investigate the transport properties of photo-injected electrons and holes within the phosphor layer of the ACTFEL device. VIQ experiments use a broadband xenon lamp pulse to optically reset traps which are ionized by subthreshold bipolar voltage pulses. Both experiments characterize traps within the phosphor layer. PIQ/PIL experiments are performed on evaporated ZnS:Mn ACTFEL devices possessing phosphor layers with thicknesses of 950, 700, and 300 nm. From the PIQ/PIL experiment, an impact excitation threshold electric field for evaporated ZnS:Mn is found to be ~1 MV/cm. Evidence of hole-trapping is also obtained from the PIQ experiment. The holes in evaporated ZnS:Mn ACTFEL devices are found to possess a drift length of ~180 ± 70 nm, a hole lifetime of ~2 ps, and a capture cross-section of ~7 x 10⁻¹³ cm². It is speculated that the trap responsible for hole capture is a zinc vacancy or zinc vacancy complex. VIQ experiments are performed on evaporated, atomic layer epitaxy [ALE] (Cl), and ALE (DEZ) ZnS:Mn ACTFEL devices. Data obtained via VIQ experiments yield evidence for the generation of space charge below the EL conduction threshold, as well as providing a means of estimating the physical location, energy depth, density, and capture cross-section of traps responsible for VIQ. The depth of the traps responsible for VIQ in evaporated, ALE (C1), and ALE (DEZ) ZnS:Mn are estimated to be ~1.1, ~0.3, and ~0.8 eV, respectively. It is speculated that the traps responsible for VIQ are due to sulfur vacancies, chlorine, and oxygen, for evaporated, ALE (Cl), and ALE (DEZ), respectively.
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