| Summary: | 博士 === 國立臺灣大學 === 光電工程學研究所 === 96 === In this dissertation, we first demonstrate the variations of the photoluminescence (PL) spectral peak position and intensity through the surface plasmon (SP) coupling with an InGaN/GaN quantum-well (QW) by forming Ag nanostructures of different scale sizes on the QW structure with thermal annealing. By transferring an Ag thin film into a nano-island structure, we can not only enhance the PL intensity, but also adjust the SP dispersion relation and hence red-shift the effective QW emission wavelength. Also, the leakage of SP through the Ohmic contact of either p-type or n-type GaN layer in the coupling process between SP and an InGaN/GaN QW is studied. It is shown that the PL intensity is significantly reduced when an Ohmic contact is formed, in contrast to the case of significant PL enhancement when an insulating thin layer is applied between the doped semiconductor and metal.
For practical application of the QW-SP coupling, we study the coupling effects between the QW and SP generated nearby on the p-type side in a blue InGaN/GaN single-QW LED. The QW-SP coupling leads to the enhancement of the electroluminescence (EL) intensity in the LED sample designed for QW-SP coupling and reduced SP energy leakage, when compared to an LED sample of weak QW-SP coupling or significant SP energy loss. Meanwhile, the output enhancement of a green InGaN/GaN QW LED through the coupling of QW with localized surface plasmons (LSPs), which are generated on Ag nanostructures on the top of the device, is also demonstrated. The suitable Ag nanostructures for generating LSPs of resonance energies around the LED wavelength are formed by controlling the Ag deposition thickness and the post-thermal-annealing condition. With a 20 mA current injected onto the LED, enhancements of up to 150 % in electroluminescence peak intensity and of 120 % in integrated intensity are observed.
Besides, blue-red polychromatic light-emitting devices are fabricated by attaching red-emitting CdSe/ZnS nano-crystals (NCs) on a blue-emitting InGaN/GaN multiple-quantum-well (MQW) structure. To improve the red/blue intensity contrast, holes of different diameters are fabricated for increasing the direct contact area between the MQW active regions and CdSe/ZnS NCs. In addition, we demonstrate the implementation of a white-light device by spin-coating CdSe/ZnS NCs on the top of a blue/green two-color InGaN/GaN QW LED for converting blue and green emissions into red light through the absorption/reemission process. Meanwhile, Au nano-particles (NPs) are mixed with CdSe/ZnS NCs for generating LSP modes to couple with the CdSe/ZnS NCs. The LSP modes can absorb green emission and effectively transfer the energy into the CdSe/ZnS NCs through the coupling process for enhancing red emission. With the LSP coupling process, the conversion efficiency from the blue/green range into red light can be increased by around 30 %. The conversion quantum efficiency can reach 52.8 %.
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