Thesis

High performance microstructured light emitting diodes : mechanisms and processes

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Awarding institution
  • University of Strathclyde
Date of award
  • 2013
Thesis identifier
  • T13420
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Department, School or Faculty
Abstract
  • The research work presented in this thesis focuses on the mechanisms and development of novel III-nitride microstructured light emitting diodes (LEDs). In particular, we focus on micro-sized LEDs (`µ-LEDs') and LEDs containing micro- scale emission images i.e. `microstructured-image LEDs'. III-nitride µ-LEDs, which are devices with dimensions less than 100 µm, show improved device performance and novel potential applications compared with broad- area LEDs. The internal electric field in III-nitride materials, which is mainly caused by the strain due to lattice mismatch with the substrate, is a serious issue for III-nitride LEDs. As the strain can be relaxed in micro-scale structures, the performance of µ-LEDs can be improved. In this work, we have investigated the strain relaxation process in III-nitride micro-pillars as a function of pillar diameter by high-spatial-resolution cathodoluminescence. The results of this study give a guideline for further design of µ-LEDs with high efficiency. The internal electric field can also be screened by injection of carriers, leading to a blue-shift of the emission wavelength for III-nitride LEDs. Due to the high operating current density that µ-LEDs can sustain, the magnitude of this blue-shift is remarkably increased for µ-LEDs. Based on this characteristic, colour-tunable µ-LEDs have been demonstrated in this work, which offers a simple way to achieve multi-colour displays. In order to further improve the performance of µ-LEDs, we have also developed Pd-based contacts to p-type GaN and investigated the current-density dependent specific contact resistivity. At high current densities, the µ-LEDs with optimized Pd-based contacts have better electrical performance compared with devices using oxidized Ni/Au contacts. The optimized Pd-based contact also leads to improved optical power for blue LEDs in flip-chip configurations. III-nitride microstructured-image LEDs are devices in which micro-scale emission patterns are created in single LEDs. These devices offer a simple approach to the display of high-resolution images. CHF3 plasma treatment is a novel technique used for the fabrication of these devices. This plasma treatment can locally modify the electrical properties of p-type GaN and define the emission image. An application of these devices for maskless image writing is demonstrated.
Resource Type
DOI
Date Created
  • 2013
Former identifier
  • 990138

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