Projects per year
This thesis addresses the lack of an efficient semiconductor light source at green emission colours. Considering InGaN based quantum-well (QW) light-emitters and light-emitting diodes (LEDs), various ways of applying surface plasmonics and nano-patterning to improve the efficiency, are investigated. By placing metallic thin films or nanoparticles (NPs) in the near-field of QW light-emitters, it is possible to improve their internal quantum efficiency (IQE) through the Purcell enhancement effect. It has been a general understanding that in order to achieve surface plasmon (SP) coupling with QWs and thereby IQE enhancement, the metal NP resonance should match the emission wavelength. This criterion is critically analysed, and based on the experimental findings, a more complicated relation is revealed. The requirements which must be satisfied to avoid optical suppression are presented. The SP-QW coupling does not necessarily lead to emission enhancement. The findings of this work show that the scattering and absorption properties of NPs play a crucial role in determining whether the implementation will improve or degrade the optical performance. By applying these principles, a novel design is presented to obtain light extraction efficiency (LEE) improvement through nano-patterning, and IQE improvement through SP-QW coupling. Considering the fabrication process aspect, dry-etching damage on the semiconductor light-emitters from the nano-patterning is also addressed. Different ion-damage treatment methods are presented to improve the efficiency of the QWs. Furthermore, a design for electrically driven LED device with SP compatibility is proposed, and requirements on p-type GaN layer thickness and current spreading properties are investigated experimentally.
|Technical University of Denmark
|Number of pages
|Published - 2015