Enhancement of the light outcoupling of alternating current laterally emitting thin film electroluminescent devices

Barros, S.O., 2000. Enhancement of the light outcoupling of alternating current laterally emitting thin film electroluminescent devices. PhD, Nottingham Trent University.

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Brightness enhancement of Laterally Emitting Thin Film Electroluminescent (LETFEL) devices is essential for polychrome display applications. Brightness values can be increased by improvement of the outcoupling efficiency. This thesis presents work carried out towards the analysis and development of the outcoupling mechanism integrated within LETFEL devices. Special importance is given to the enhancement of the coupling efficiency for head mounted displays (HMD) and electrophotographic printing (EP) applications for which high brightness and narrow angular profiles are advantageous.

This research introduces a theoretical study of the light transmission within a LETFEL device, based on the modal propagation theory in an optical waveguide. Losses due to surface roughness were determined and compared with previously published experimental results. Agreement between the fundamental mode attenuation loss, theoretically calculated, and the total attenuation loss, experimentally determined, demonstrated transmission is principally supported by the fundamental mode.

Based upon this result, modelling of the outcoupling efficiency in conventional devices was performed assuming outcoupling was due to surface roughness and bend radiation losses. Low outcoupling efficiency values, of the order of 4% of the generated light, were obtained. This, in addition to the inadequate broad angular profiles experimentally determined, demonstrated need for improvement.

The presented work has concentrated on the proposal of two novel outcoupling mechanisms: the surface emitting edge emitter and the etched aperture. Initial modelling of the emitted angular distribution demonstrates a Gaussian angular profile, with a characteristic width of 24°.

The feasibility of fabrication of these structures using ion milling was additionally proved. Initially, a study was undertaken of the ion milling properties of LETFEL devices and associated materials. The principal parameters considered were the etching time, the acceleration voltage and the angle of incidence of the ion beam. Subsequently the fabrication and determination of the light output properties of full devices demonstrated a ?2x and ?4x enhancement of the light intensity for the etched and surface emitting edge emitter devices respectively. Additionally, the angular profile of etched devices was observed to redistribute towards narrower angles of view which introduces further enhancement of the coupling efficiency, by 12% and 5% for HMD and EP respectively. The angular distribution of surface emitting edge emitter LETFEL devices was found to be in agreement with the theoretical results.

Item Type: Thesis
Creators: Barros, S.O.
Date: 2000
ISBN: 9781369325577
Divisions: Schools > School of Science and Technology
Record created by: Laura Ward
Date Added: 06 Jul 2021 09:17
Last Modified: 10 Apr 2024 14:54
URI: https://irep.ntu.ac.uk/id/eprint/43334

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