| Summary: | 碩士 === 南台科技大學 === 光電工程系 === 100 === In the past years, the efficiency of GaN- based LEDs has been greatly improved. Therefore, it makes general lighting using semiconductor emitters not only a dream. In other words, the traditional lighting devices, such as incandescent lamps and fluorescent tubes, will be replaced by the white LEDs in the near future. In addition to the efficiency issue, cost is still a bottle neck for using white LEDs to replace traditional lighting devices totally. In brief, the lm/$(lumen/per dollar) of white LEDs is still too high compared with traditional lighting devices. Therefore, how to improve further the efficiency of LEDs using low-cost technology is a key issue to reach the target. Considering the technical issues, the light extraction efficiency (LEE) and the external quantum efficiency (EQE) of GaN-based LEDs need to be further raised. In order to increase the LEE many approaches have been proposed, such as omnidirectional reflectors, flip-chip packaging, photonic crystals, surface roughening and pattern sapphire substrate. However, each technique has its own processing and cost drawbacks when applied to large-scale production, in these cases.
In this study, air gaps were embedded in GaN layer to improve light output power of InGaN-based light-emitting diodes (LEDs) due to the light scattering taking place at the GaN/sapphire interface. Periodic metal patterns deposited on sapphire and then underwent thermal annealing was performed to form patterned surface of sapphire substrates. In principle, the lattice of locally diffused area would be disordered. Therefore, the GaN grown on the diffused areas had a lower growth rate than the diffusion-free area. Without using a patterned dielectric thin film like as the lateral epitaxial overgrowth technique, air gaps formed above the diffusion regions and below the active layers of InGaN LEDs. We proposed the growth mechanisms of GaN layer on the patterned sapphire and characterized the InGaN-based LEDs with embedded air gaps array.
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