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Proceedings Paper

Simulation of nanoscale ITO top grating of GaN LED
Author(s): Gabriel Halpin; Xiaomin Jin; Greg Chavoor; Xing-Xing Fu; Xiang-Ning Kang; Guo-Yi Zhang
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Paper Abstract

Today’s advanced technology allows engineers to fabricate GaN LEDs with various heights, widths, shapes, and materials. Total internal reflection is a key factor in GaN LED design, because all light that is created inside the LED is lost unless it approaches the chip to air interface at an angle less than 23.58° with respect to the normal. The narrow range of angles at which light can successfully escape the chip is a result of the large difference in refractive indices between GaN and air. Adding a layer of ITO to the GaN reduces the difference in refractive indices between steps and increases the critical angle to 28.4°. Transmitting from ITO into epoxy reduces this difference in refractive indices again, bringing the critical angle to 47.9°. Because a higher critical angle should allow more light to escape the LED, we focus on enhancing light extraction efficiency of GaN LED's that utilize an ITO to epoxy interface using FDTD simulations. The simulation results show us that increasing the critical angle to 47.9° improves light extraction by 40%, proving that the critical angle does play a significant role in light extraction. From this initial result, we then compare light extraction efficiencies of ITO and GaN gratings over varied grating periods, and show that adding an Ag reflection layer improves overall efficiency. Finally, we show that the light extraction for LED's utilizing an Ag reflection layer is highly dependent on the sapphire substrate thickness.

Paper Details

Date Published: 14 March 2013
PDF: 8 pages
Proc. SPIE 8619, Physics and Simulation of Optoelectronic Devices XXI, 86190I (14 March 2013); doi: 10.1117/12.2001071
Show Author Affiliations
Gabriel Halpin, California Polytechnic State Univ., San Luis Obispo (United States)
Xiaomin Jin, California Polytechnic State Univ., San Luis Obispo (United States)
Peking Univ. (China)
Greg Chavoor, California Polytechnic State Univ., San Luis Obispo (United States)
Xing-Xing Fu, Peking Univ. (China)
Xiang-Ning Kang, Peking Univ. (China)
Guo-Yi Zhang, Peking Univ. (China)


Published in SPIE Proceedings Vol. 8619:
Physics and Simulation of Optoelectronic Devices XXI
Bernd Witzigmann; Marek Osinski; Fritz Henneberger; Yasuhiko Arakawa, Editor(s)

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