Light-emitting Devices Based on InGaN/GaN Nano-structures

Autor: Horng-Shyang Chen, 陳鴻祥
Rok vydání: 2006
Druh dokumentu: 學位論文 ; thesis
Popis: 94
In this research, we systematically investigate of InGaN/GaN quantum-well (QW) light-emitting diodes (LEDs) design and optics characteristics. First, we have grown and process a blue/green two-wavelength LED based on the mixture of two kinds of QW in epitaxial growth. We then coat CdSe/ZnS nano-crystals on the top of the two-wavelength LED for converting blue photons into red light. By coating such nano-crystals, the device emitted blue, green, and red lights for white-light generation. Also, we have fabricated blue/green two-wavelength, InGaN/GaN QW, flip-chip micro-LEDs of different mesa sizes by stacking different QWs. It is found that the blue-over-green contrast ratio of such an LED increased with the mesa size. The relatively stronger blue intensity in a device of larger mesa area is due to its higher operation junction temperature. For the emissions of yellow, orange, and red colors in InGaN/GaN QW LEDs, higher indium contents must be incorporated. Because of the 11 % lattice mismatch between GaN and InN, the miscibility between the two binary compounds becomes difficult when the indium content is higher than 15 % or so. We have demonstrated the operations of an orange and a red LED, which are fabricated with a pre-strained InGaN/GaN QW epi-structure. The pre-strain condition is created by growing a low-indium QW before the growth of five high-indium QWs. Finally, nanoposts with diameter down to around 10 nm are fabricated using electron-beam lithography and ICP RIE on an InGaN/GaN QW structure. Significant blue shifts in the PL spectra are observed. The blue shift range increases with decreasing post diameter. For the nanoposts with significant strain relaxation, the PL spectral peak positions became less sensitive to carrier screening. From the temperature-dependent PL and TRPL measurements and a numerical calculation of the effect of quantum confinement, we conclude that the optical behaviors of the nanoposts are mainly controlled by the combined effect of 3D quantum confinement and strain relaxation.
Databáze: Networked Digital Library of Theses & Dissertations
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