GaN-Based Light-Emitting Diodes With Pillar Structures Around the Mesa Region
ABSTRACT This study presents the numerical and experimental demonstrations for the enhancement of light extraction efficiency in nitride-based light-emitting diodes (LEDs) with textured sidewall and micro-sized pillar waveguides (TSMPW) and nano-textured sidewall and nano-pillars (NTSNP) around the mesa. Using hydrothermal ZnO nanorods as the etching hard mask, the authors successfully formed vertical GaN nano-pillars on the mesa-etched regions. It was found that electrical characteristics observed from the proposed LEDs were near the same as the control samples without the pillars. Output power enhancement of LED with TSMPW was about 11% compared with conventional LEDs, and the output power enhancement of LED was greater than 45% upon replacement of TSMPW with the NTSNP structure. The light extraction efficiency enhancement factors of the LEDs with TSMPW and NTSNP structures simulated by finite-difference time-domain analysis were 16.6% and 23%, respectively.
- Thin Solid Films 07/2013; · 1.87 Impact Factor
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ABSTRACT: The n-side-up vertical light emitting diodes (LEDs) have the advantage of carving the surface of the thick n-GaN layer to improve light extraction and to adjust radiation profiles. In this paper, a two-step surface patterning is employed with the focus on understanding angular light diffractions from both nanopatterns and truncated microdomes. Light output enhancement of the LEDs with hybrid surface texturing is investigated experimentally and theoretically. The results suggest that light is diffracted through the grating effect and curved sidewalls when interacting with truncated microdomes, resulting in a maximum enhancement 64° away from the normal surface. On the other hand, nearly omni-directional enhancement was found from the randomly scattered nanopatterns. As for the hybrid structure, since guided modes in the semiconductor layers are diffracted by either nanopatterns or microdomes, the percentage increase of light extraction from the hybrid structure is approximately the linear superposition of both types of surface textures. The results suggest an interesting guideline to improve LED light output and to adjust angular radiation with the mutlistep surface patterning.IEEE Journal of Quantum Electronics 01/2013; 49(1):11-16. · 2.11 Impact Factor
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ABSTRACT: Uniform spreading of injection current in light-emitting diodes (LEDs) is one of the crucial requirements for better device performances. It is reported that non-uniform current spreading leads to low output power, high current crowding, heating, and reliability degradation of the LED device. This paper reports on the effects of different surface and electrode geometries in the LEDs. To increase the output power of LEDs and reduce the series resistance, a rectangular-type LED (RT-LED) with a centered island cathode has been fabricated and investigated by comparison with a conventional LED (CV-LED). The performances of RT-LEDs were prominently enhanced via uniform current spreading and low current crowding. Performances in terms of increased output power and lower forward voltage of simulated RT-LEDs are much superior to those of CV-LEDs. Based on these results, we investigated the correlation between device geometries and optical characteristics through the fabricated CV and RT-LEDs. The measured output power and forward voltage of the RT-LEDs at 100 mA are 64.7% higher and 8% smaller compared with those of the CV-LEDs.Journal of the Optical Society of Korea 12/2012; · 0.96 Impact Factor