| Summary: | 博士 === 國立交通大學 === 光電工程系所 === 96 === Light-emitting diodes (LEDs) are revolutionizing the world. Due to the unique characteristics of III-V compound semiconductor that provides the direct transfer of electrical energy into light, LEDs have been forecasted as lighting sources of next generation. However, efficiency of present state-of-the-art visible-spectrum LEDs are still low, as compared to that of conventional lighting sources specifically applied for high-flux utilization. In addition, since concerns of energy-conservation and environment-protection become emergent over the world, the desire for more sophisticated and high-efficiency LEDs structure’s designs is even intense than ever.
In the first section of this thesis, we design a novel structure to simultaneously enhance both internal quantum efficiency and light extraction efficiency of InGaN-based LEDs.
For InGaN-based LEDs, in addition to the total internal reflection restricting photons extraction, the major difficulty is the lack of low-cost, single-crystal GaN to use as a growth substrate. Thus bunches of dislocation defects are normally observed inside active regions and served as nonradiative recombination centers. To alleviate these issues, we propose a novel structure of InGaN-based LEDs grown on chemical wet etching-patterned sapphire substrate (CWE-PSS) for simultaneously enhancing both internal quantum and light extraction efficiencies. The detail of physical mechanisms responsible for the dual enhancement in internal quantum efficiency and light extraction efficiency are also investigated in this thesis.
In the very end of this thesis, to alleviate the phosphor-convention issue commonly observed in conventional white light LEDs, phosphor-free InGaN-based dichromatic-color blue/green (470-nm/550-nm) LEDs are well designed and successfully fabricated by using sapphire laser lift-off (LLO) and wafer-bonding schemes. Flat and broad EL spectra with combination of blue and green colors are emitted, accompanying with the maximum luminous efficiency of 120lm/W. This integrated dichromatic lighting structure has a great potential to facilitate the early coming of solid-state lighting.
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