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 authors have fabricated the surface-textured GaN based light emitting diodes (LEDs) by incorporating a transparent powder onto an indium tin oxide (ITO) surface and exposed n-GaN surface to improve the light extraction efficiency by decreasing the total internal reflection and by achieving an angular randomization of the photons. The ITO surface and exposed n-GaN surface was simultaneously textured using a method known as natural lithography. The Al2O3 powders were coated onto the LED surface as a random mask for dry etching. After packaging, the light output powers of the LEDs with the textured ITO layer and with nanorods at n-GaN were enhanced about ∼ 11 and 15 %, respectively, compared with that of the conventional LED. Also, the light output power of the LED with both the textured ITO layer and the formed n-GaN nanorods increased by ∼ 24% compared with that of the conventional LED.Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2012; 30(3):0607-. · 1.36 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