Abstract

Blue GaN light emitting diodes (LEDs) in the shape of cuboids and circular disks have been fabricated by laser micromachining. The proposed circular geometry serves to enhance overall light extraction on a macro-scale and to improve uniformity of the emission pattern due to the rotational symmetry of the chip. Analysis of the chip shaping effect is carried out by ray-tracing simulations and further supported with mathematical modeling using ideal LED models, and subsequently verified with fabricated devices. In comparison, a 10% improvement in overall emission was observed for circular LEDs over the regular cuboids, consistent with simulations and calculations. The measured emission pattern from the circular LED confirms the axial symmetry of the emission beam.

© 2009 OSA

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  1. D. S. Han, J. Y. Kim, S. I. Na, S. H. Kim, K. D. Lee, B. Kim, and S. J. Park, “Improvement of light extraction efficiency of flip-chip light-emitting diode by texturing the bottom side-surface of sapphire substrate,” IEEE Photon. Technol. Lett. 18(13), 1406–1408 (2006).
    [CrossRef]
  2. T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855–857 (2004).
    [CrossRef]
  3. H. W. Choi, M. D. Dawson, P. R. Edwards, and R. W. Martin, “High extraction efficiency InGaN micro-ring light-emitting diodes,” Appl. Phys. Lett. 83(22), 4483–4485 (2003).
    [CrossRef]
  4. S. X. Jin, J. Li, J. Y. Lin, and H. X. Jiang, “InGaN/GaN quantum well interconnected microdisk light emitting diodes,” Appl. Phys. Lett. 77(20), 3236–3238 (2000).
    [CrossRef]
  5. W. N. Ng, C. H. Leung, P. T. Lai, and H. W. Choi, “Photonic crystal light-emitting diodes fabricated by microsphere lithography,” Nanotechnology 19(25), 255302 (2008).
    [CrossRef] [PubMed]
  6. P. Royo, R. P. Stanley, and A. Ilegems, “Analytical Calculation of the Extraction Efficiency of Microcavity Light-Emitting Diodes for Display and Fiber Coupling Applications,” IEEE J. Sel. Top. Quantum Electron. 8(2), 207–218 (2002).
    [CrossRef]
  7. D. S. Liu, T. W. Lin, B. W. Huang, F. S. Juang, P. H. Lei, and C. Z. Hu, “Light-extraction enhancement in GaN-based light-emitting diodes using grade-refractive-index amorphous titanium oxide films with porous structures,” Appl. Phys. Lett. 94(14), 143502 (2009).
    [CrossRef]
  8. C. Wiesmann, K. Bergenek, N. Linder, and U. T. Schwarz, “Photonic crystal LEDs – designing light extraction,” Laser Photonics Rev. 3(3), 262–286 (2009).
    [CrossRef]
  9. W. Y. Fu, K. N. Hui, X. H. Wang, K. K. Y. Wong, P. T. Lai, and H. W. Choi, “Geometrical Shaping of InGaN Light-emitting Diodes by Laser Micromachining,” IEEE Photon. Technol. Lett. 21(15), 1078–1080 (2009).
    [CrossRef]
  10. C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
    [CrossRef]
  11. X. H. Wang, P. T. Lai, and H. W. Choi, “Laser Micro-machining of Optical Microstructures with Inclined Sidewall Profile,” J. Vac. Sci. Technol. B 27(3), 1048–1052 (2009).
    [CrossRef]

2009 (4)

D. S. Liu, T. W. Lin, B. W. Huang, F. S. Juang, P. H. Lei, and C. Z. Hu, “Light-extraction enhancement in GaN-based light-emitting diodes using grade-refractive-index amorphous titanium oxide films with porous structures,” Appl. Phys. Lett. 94(14), 143502 (2009).
[CrossRef]

C. Wiesmann, K. Bergenek, N. Linder, and U. T. Schwarz, “Photonic crystal LEDs – designing light extraction,” Laser Photonics Rev. 3(3), 262–286 (2009).
[CrossRef]

W. Y. Fu, K. N. Hui, X. H. Wang, K. K. Y. Wong, P. T. Lai, and H. W. Choi, “Geometrical Shaping of InGaN Light-emitting Diodes by Laser Micromachining,” IEEE Photon. Technol. Lett. 21(15), 1078–1080 (2009).
[CrossRef]

X. H. Wang, P. T. Lai, and H. W. Choi, “Laser Micro-machining of Optical Microstructures with Inclined Sidewall Profile,” J. Vac. Sci. Technol. B 27(3), 1048–1052 (2009).
[CrossRef]

2008 (1)

W. N. Ng, C. H. Leung, P. T. Lai, and H. W. Choi, “Photonic crystal light-emitting diodes fabricated by microsphere lithography,” Nanotechnology 19(25), 255302 (2008).
[CrossRef] [PubMed]

2006 (1)

D. S. Han, J. Y. Kim, S. I. Na, S. H. Kim, K. D. Lee, B. Kim, and S. J. Park, “Improvement of light extraction efficiency of flip-chip light-emitting diode by texturing the bottom side-surface of sapphire substrate,” IEEE Photon. Technol. Lett. 18(13), 1406–1408 (2006).
[CrossRef]

2005 (1)

C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
[CrossRef]

2004 (1)

T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855–857 (2004).
[CrossRef]

2003 (1)

H. W. Choi, M. D. Dawson, P. R. Edwards, and R. W. Martin, “High extraction efficiency InGaN micro-ring light-emitting diodes,” Appl. Phys. Lett. 83(22), 4483–4485 (2003).
[CrossRef]

2002 (1)

P. Royo, R. P. Stanley, and A. Ilegems, “Analytical Calculation of the Extraction Efficiency of Microcavity Light-Emitting Diodes for Display and Fiber Coupling Applications,” IEEE J. Sel. Top. Quantum Electron. 8(2), 207–218 (2002).
[CrossRef]

2000 (1)

S. X. Jin, J. Li, J. Y. Lin, and H. X. Jiang, “InGaN/GaN quantum well interconnected microdisk light emitting diodes,” Appl. Phys. Lett. 77(20), 3236–3238 (2000).
[CrossRef]

Bergenek, K.

C. Wiesmann, K. Bergenek, N. Linder, and U. T. Schwarz, “Photonic crystal LEDs – designing light extraction,” Laser Photonics Rev. 3(3), 262–286 (2009).
[CrossRef]

Choi, H. W.

W. Y. Fu, K. N. Hui, X. H. Wang, K. K. Y. Wong, P. T. Lai, and H. W. Choi, “Geometrical Shaping of InGaN Light-emitting Diodes by Laser Micromachining,” IEEE Photon. Technol. Lett. 21(15), 1078–1080 (2009).
[CrossRef]

X. H. Wang, P. T. Lai, and H. W. Choi, “Laser Micro-machining of Optical Microstructures with Inclined Sidewall Profile,” J. Vac. Sci. Technol. B 27(3), 1048–1052 (2009).
[CrossRef]

W. N. Ng, C. H. Leung, P. T. Lai, and H. W. Choi, “Photonic crystal light-emitting diodes fabricated by microsphere lithography,” Nanotechnology 19(25), 255302 (2008).
[CrossRef] [PubMed]

H. W. Choi, M. D. Dawson, P. R. Edwards, and R. W. Martin, “High extraction efficiency InGaN micro-ring light-emitting diodes,” Appl. Phys. Lett. 83(22), 4483–4485 (2003).
[CrossRef]

Chu, J. T.

C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
[CrossRef]

Dawson, M. D.

H. W. Choi, M. D. Dawson, P. R. Edwards, and R. W. Martin, “High extraction efficiency InGaN micro-ring light-emitting diodes,” Appl. Phys. Lett. 83(22), 4483–4485 (2003).
[CrossRef]

DenBaars, S. P.

T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855–857 (2004).
[CrossRef]

Edwards, P. R.

H. W. Choi, M. D. Dawson, P. R. Edwards, and R. W. Martin, “High extraction efficiency InGaN micro-ring light-emitting diodes,” Appl. Phys. Lett. 83(22), 4483–4485 (2003).
[CrossRef]

Fu, W. Y.

W. Y. Fu, K. N. Hui, X. H. Wang, K. K. Y. Wong, P. T. Lai, and H. W. Choi, “Geometrical Shaping of InGaN Light-emitting Diodes by Laser Micromachining,” IEEE Photon. Technol. Lett. 21(15), 1078–1080 (2009).
[CrossRef]

Fujii, T.

T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855–857 (2004).
[CrossRef]

Gao, Y.

T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855–857 (2004).
[CrossRef]

Han, D. S.

D. S. Han, J. Y. Kim, S. I. Na, S. H. Kim, K. D. Lee, B. Kim, and S. J. Park, “Improvement of light extraction efficiency of flip-chip light-emitting diode by texturing the bottom side-surface of sapphire substrate,” IEEE Photon. Technol. Lett. 18(13), 1406–1408 (2006).
[CrossRef]

Hsieh, Y. L.

C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
[CrossRef]

Hu, C. Z.

D. S. Liu, T. W. Lin, B. W. Huang, F. S. Juang, P. H. Lei, and C. Z. Hu, “Light-extraction enhancement in GaN-based light-emitting diodes using grade-refractive-index amorphous titanium oxide films with porous structures,” Appl. Phys. Lett. 94(14), 143502 (2009).
[CrossRef]

Hu, E. L.

T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855–857 (2004).
[CrossRef]

Huang, B. W.

D. S. Liu, T. W. Lin, B. W. Huang, F. S. Juang, P. H. Lei, and C. Z. Hu, “Light-extraction enhancement in GaN-based light-emitting diodes using grade-refractive-index amorphous titanium oxide films with porous structures,” Appl. Phys. Lett. 94(14), 143502 (2009).
[CrossRef]

Huang, H. W.

C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
[CrossRef]

Hui, K. N.

W. Y. Fu, K. N. Hui, X. H. Wang, K. K. Y. Wong, P. T. Lai, and H. W. Choi, “Geometrical Shaping of InGaN Light-emitting Diodes by Laser Micromachining,” IEEE Photon. Technol. Lett. 21(15), 1078–1080 (2009).
[CrossRef]

Ilegems, A.

P. Royo, R. P. Stanley, and A. Ilegems, “Analytical Calculation of the Extraction Efficiency of Microcavity Light-Emitting Diodes for Display and Fiber Coupling Applications,” IEEE J. Sel. Top. Quantum Electron. 8(2), 207–218 (2002).
[CrossRef]

Jiang, H. X.

S. X. Jin, J. Li, J. Y. Lin, and H. X. Jiang, “InGaN/GaN quantum well interconnected microdisk light emitting diodes,” Appl. Phys. Lett. 77(20), 3236–3238 (2000).
[CrossRef]

Jin, S. X.

S. X. Jin, J. Li, J. Y. Lin, and H. X. Jiang, “InGaN/GaN quantum well interconnected microdisk light emitting diodes,” Appl. Phys. Lett. 77(20), 3236–3238 (2000).
[CrossRef]

Juang, F. S.

D. S. Liu, T. W. Lin, B. W. Huang, F. S. Juang, P. H. Lei, and C. Z. Hu, “Light-extraction enhancement in GaN-based light-emitting diodes using grade-refractive-index amorphous titanium oxide films with porous structures,” Appl. Phys. Lett. 94(14), 143502 (2009).
[CrossRef]

Kao, C. C.

C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
[CrossRef]

Kim, B.

D. S. Han, J. Y. Kim, S. I. Na, S. H. Kim, K. D. Lee, B. Kim, and S. J. Park, “Improvement of light extraction efficiency of flip-chip light-emitting diode by texturing the bottom side-surface of sapphire substrate,” IEEE Photon. Technol. Lett. 18(13), 1406–1408 (2006).
[CrossRef]

Kim, J. Y.

D. S. Han, J. Y. Kim, S. I. Na, S. H. Kim, K. D. Lee, B. Kim, and S. J. Park, “Improvement of light extraction efficiency of flip-chip light-emitting diode by texturing the bottom side-surface of sapphire substrate,” IEEE Photon. Technol. Lett. 18(13), 1406–1408 (2006).
[CrossRef]

Kim, S. H.

D. S. Han, J. Y. Kim, S. I. Na, S. H. Kim, K. D. Lee, B. Kim, and S. J. Park, “Improvement of light extraction efficiency of flip-chip light-emitting diode by texturing the bottom side-surface of sapphire substrate,” IEEE Photon. Technol. Lett. 18(13), 1406–1408 (2006).
[CrossRef]

Kuo, H. C.

C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
[CrossRef]

Lai, P. T.

W. Y. Fu, K. N. Hui, X. H. Wang, K. K. Y. Wong, P. T. Lai, and H. W. Choi, “Geometrical Shaping of InGaN Light-emitting Diodes by Laser Micromachining,” IEEE Photon. Technol. Lett. 21(15), 1078–1080 (2009).
[CrossRef]

X. H. Wang, P. T. Lai, and H. W. Choi, “Laser Micro-machining of Optical Microstructures with Inclined Sidewall Profile,” J. Vac. Sci. Technol. B 27(3), 1048–1052 (2009).
[CrossRef]

W. N. Ng, C. H. Leung, P. T. Lai, and H. W. Choi, “Photonic crystal light-emitting diodes fabricated by microsphere lithography,” Nanotechnology 19(25), 255302 (2008).
[CrossRef] [PubMed]

Lee, K. D.

D. S. Han, J. Y. Kim, S. I. Na, S. H. Kim, K. D. Lee, B. Kim, and S. J. Park, “Improvement of light extraction efficiency of flip-chip light-emitting diode by texturing the bottom side-surface of sapphire substrate,” IEEE Photon. Technol. Lett. 18(13), 1406–1408 (2006).
[CrossRef]

Lei, P. H.

D. S. Liu, T. W. Lin, B. W. Huang, F. S. Juang, P. H. Lei, and C. Z. Hu, “Light-extraction enhancement in GaN-based light-emitting diodes using grade-refractive-index amorphous titanium oxide films with porous structures,” Appl. Phys. Lett. 94(14), 143502 (2009).
[CrossRef]

Leung, C. H.

W. N. Ng, C. H. Leung, P. T. Lai, and H. W. Choi, “Photonic crystal light-emitting diodes fabricated by microsphere lithography,” Nanotechnology 19(25), 255302 (2008).
[CrossRef] [PubMed]

Li, J.

S. X. Jin, J. Li, J. Y. Lin, and H. X. Jiang, “InGaN/GaN quantum well interconnected microdisk light emitting diodes,” Appl. Phys. Lett. 77(20), 3236–3238 (2000).
[CrossRef]

Lin, C. F.

C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
[CrossRef]

Lin, J. Y.

S. X. Jin, J. Li, J. Y. Lin, and H. X. Jiang, “InGaN/GaN quantum well interconnected microdisk light emitting diodes,” Appl. Phys. Lett. 77(20), 3236–3238 (2000).
[CrossRef]

Lin, T. W.

D. S. Liu, T. W. Lin, B. W. Huang, F. S. Juang, P. H. Lei, and C. Z. Hu, “Light-extraction enhancement in GaN-based light-emitting diodes using grade-refractive-index amorphous titanium oxide films with porous structures,” Appl. Phys. Lett. 94(14), 143502 (2009).
[CrossRef]

Linder, N.

C. Wiesmann, K. Bergenek, N. Linder, and U. T. Schwarz, “Photonic crystal LEDs – designing light extraction,” Laser Photonics Rev. 3(3), 262–286 (2009).
[CrossRef]

Liu, D. S.

D. S. Liu, T. W. Lin, B. W. Huang, F. S. Juang, P. H. Lei, and C. Z. Hu, “Light-extraction enhancement in GaN-based light-emitting diodes using grade-refractive-index amorphous titanium oxide films with porous structures,” Appl. Phys. Lett. 94(14), 143502 (2009).
[CrossRef]

Luo, C. Y.

C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
[CrossRef]

Martin, R. W.

H. W. Choi, M. D. Dawson, P. R. Edwards, and R. W. Martin, “High extraction efficiency InGaN micro-ring light-emitting diodes,” Appl. Phys. Lett. 83(22), 4483–4485 (2003).
[CrossRef]

Na, S. I.

D. S. Han, J. Y. Kim, S. I. Na, S. H. Kim, K. D. Lee, B. Kim, and S. J. Park, “Improvement of light extraction efficiency of flip-chip light-emitting diode by texturing the bottom side-surface of sapphire substrate,” IEEE Photon. Technol. Lett. 18(13), 1406–1408 (2006).
[CrossRef]

Nakamura, S.

T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855–857 (2004).
[CrossRef]

Ng, W. N.

W. N. Ng, C. H. Leung, P. T. Lai, and H. W. Choi, “Photonic crystal light-emitting diodes fabricated by microsphere lithography,” Nanotechnology 19(25), 255302 (2008).
[CrossRef] [PubMed]

Park, S. J.

D. S. Han, J. Y. Kim, S. I. Na, S. H. Kim, K. D. Lee, B. Kim, and S. J. Park, “Improvement of light extraction efficiency of flip-chip light-emitting diode by texturing the bottom side-surface of sapphire substrate,” IEEE Photon. Technol. Lett. 18(13), 1406–1408 (2006).
[CrossRef]

Peng, Y. C.

C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
[CrossRef]

Royo, P.

P. Royo, R. P. Stanley, and A. Ilegems, “Analytical Calculation of the Extraction Efficiency of Microcavity Light-Emitting Diodes for Display and Fiber Coupling Applications,” IEEE J. Sel. Top. Quantum Electron. 8(2), 207–218 (2002).
[CrossRef]

Schwarz, U. T.

C. Wiesmann, K. Bergenek, N. Linder, and U. T. Schwarz, “Photonic crystal LEDs – designing light extraction,” Laser Photonics Rev. 3(3), 262–286 (2009).
[CrossRef]

Sharma, R.

T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855–857 (2004).
[CrossRef]

Stanley, R. P.

P. Royo, R. P. Stanley, and A. Ilegems, “Analytical Calculation of the Extraction Efficiency of Microcavity Light-Emitting Diodes for Display and Fiber Coupling Applications,” IEEE J. Sel. Top. Quantum Electron. 8(2), 207–218 (2002).
[CrossRef]

Wang, S. C.

C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
[CrossRef]

Wang, X. H.

X. H. Wang, P. T. Lai, and H. W. Choi, “Laser Micro-machining of Optical Microstructures with Inclined Sidewall Profile,” J. Vac. Sci. Technol. B 27(3), 1048–1052 (2009).
[CrossRef]

W. Y. Fu, K. N. Hui, X. H. Wang, K. K. Y. Wong, P. T. Lai, and H. W. Choi, “Geometrical Shaping of InGaN Light-emitting Diodes by Laser Micromachining,” IEEE Photon. Technol. Lett. 21(15), 1078–1080 (2009).
[CrossRef]

Wiesmann, C.

C. Wiesmann, K. Bergenek, N. Linder, and U. T. Schwarz, “Photonic crystal LEDs – designing light extraction,” Laser Photonics Rev. 3(3), 262–286 (2009).
[CrossRef]

Wong, K. K. Y.

W. Y. Fu, K. N. Hui, X. H. Wang, K. K. Y. Wong, P. T. Lai, and H. W. Choi, “Geometrical Shaping of InGaN Light-emitting Diodes by Laser Micromachining,” IEEE Photon. Technol. Lett. 21(15), 1078–1080 (2009).
[CrossRef]

Yu, C. C.

C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
[CrossRef]

Appl. Phys. Lett. (4)

T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855–857 (2004).
[CrossRef]

H. W. Choi, M. D. Dawson, P. R. Edwards, and R. W. Martin, “High extraction efficiency InGaN micro-ring light-emitting diodes,” Appl. Phys. Lett. 83(22), 4483–4485 (2003).
[CrossRef]

S. X. Jin, J. Li, J. Y. Lin, and H. X. Jiang, “InGaN/GaN quantum well interconnected microdisk light emitting diodes,” Appl. Phys. Lett. 77(20), 3236–3238 (2000).
[CrossRef]

D. S. Liu, T. W. Lin, B. W. Huang, F. S. Juang, P. H. Lei, and C. Z. Hu, “Light-extraction enhancement in GaN-based light-emitting diodes using grade-refractive-index amorphous titanium oxide films with porous structures,” Appl. Phys. Lett. 94(14), 143502 (2009).
[CrossRef]

IEEE J. Sel. Top. Quantum Electron. (1)

P. Royo, R. P. Stanley, and A. Ilegems, “Analytical Calculation of the Extraction Efficiency of Microcavity Light-Emitting Diodes for Display and Fiber Coupling Applications,” IEEE J. Sel. Top. Quantum Electron. 8(2), 207–218 (2002).
[CrossRef]

IEEE Photon. Technol. Lett. (3)

D. S. Han, J. Y. Kim, S. I. Na, S. H. Kim, K. D. Lee, B. Kim, and S. J. Park, “Improvement of light extraction efficiency of flip-chip light-emitting diode by texturing the bottom side-surface of sapphire substrate,” IEEE Photon. Technol. Lett. 18(13), 1406–1408 (2006).
[CrossRef]

W. Y. Fu, K. N. Hui, X. H. Wang, K. K. Y. Wong, P. T. Lai, and H. W. Choi, “Geometrical Shaping of InGaN Light-emitting Diodes by Laser Micromachining,” IEEE Photon. Technol. Lett. 21(15), 1078–1080 (2009).
[CrossRef]

C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, S. C. Wang, C. C. Yu, and C. F. Lin, “Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls,” IEEE Photon. Technol. Lett. 17(1), 19–21 (2005).
[CrossRef]

J. Vac. Sci. Technol. B (1)

X. H. Wang, P. T. Lai, and H. W. Choi, “Laser Micro-machining of Optical Microstructures with Inclined Sidewall Profile,” J. Vac. Sci. Technol. B 27(3), 1048–1052 (2009).
[CrossRef]

Laser Photonics Rev. (1)

C. Wiesmann, K. Bergenek, N. Linder, and U. T. Schwarz, “Photonic crystal LEDs – designing light extraction,” Laser Photonics Rev. 3(3), 262–286 (2009).
[CrossRef]

Nanotechnology (1)

W. N. Ng, C. H. Leung, P. T. Lai, and H. W. Choi, “Photonic crystal light-emitting diodes fabricated by microsphere lithography,” Nanotechnology 19(25), 255302 (2008).
[CrossRef] [PubMed]

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Figures (7)

Fig. 1
Fig. 1

(a) The simulated emission patterns obtained from ray tracing using LED models of cuboid and circular disk geometries, both have an emissive region of 500 µm x 500 µm. The light extraction efficiency was determined to be 12.47% and 13.43% respectively, corresponding to an overall enhancement of ~7.8% due to enhanced sidewall extraction efficiency. The extraction ratios from top-surfaces are ~83% for both models, while the circular sidewall is capable of delivering a higher extraction ratio of 52%, ~19% higher than the cuboid geometry. The simulated spatial intensity patterns at a plane near the top surfaces of the LEDs are plotted in parts (b) and (c). The corresponding models used in the simulations are illustrated in parts (d) and (e).

Fig. 2
Fig. 2

Light emissions from the MQW layers can be divided into 4 regions separated by 3 cones as shown in (a). Light rays within the first escape cone γ1 are extracted through the top surfaces exhibited by blue rays in (b). Light rays in the region between cone γ2 and γ3 contribute to sidewall extraction as traced with green rays both in (b) and (c). Rays beyond cone γ3 is confined within GaN and those between cone γ1 and γ2, shown as red rays, are forbidden to escape due to total internal reflection on the sidewall. (d) Schematic diagram showing the oval angular intensity distribution of the optical power that reaches the interface of n-GaN/Sapphire after considering the effects of absorption.

Fig. 3
Fig. 3

(a) Sidewall emission pattern of a circular LED model with and without a bottom mirror reflector. (b) Selected rays from simulation illustrating the directionality of sidewall extractions. Colors of rays indicate optical power (decreasing power from red to blue).

Fig. 4
Fig. 4

Optical microphotographs of (a) cuboid and (b) circular LEDs fabricated with laser micromachining. The devices are biased at 1 mA current.

Fig. 5
Fig. 5

L-I characteristics of the laser micro-machined cuboid LED and circular LED. Circular LED outputs 10.3% more optical power on average than the cuboid LED at the same current level.

Fig. 6
Fig. 6

(a) 3-dimentional schematic diagram illustrating two possible light rays SP1 and SQ2 that can be extracted through the planar sidewall, propagating from point S along the emission cone. (b) The projected image of the light rays in (a) onto a horizontal plane. Rays falling within the unshaded region can be extracted; (c) All light rays can be extracted when point source S is within the central circular region defined by Rc for a circularly-shaped sidewall. (d) When point source S is located beyond the central region Rc, only rays within the unshaded regions can be extracted.

Fig. 7
Fig. 7

Emission patterns measured from (a) cuboid and (b) circular LEDs at different vertical planes. The circular LED emits more uniformly with axial symmetry and approaches an ideal Lambertian pattern. The 60° plane corresponds to the plane derived by rotating the XZ plane by 60° angle about the Z axis.

Tables (2)

Tables Icon

Table 1 Optical parameters adopted in simulations (at 475 nm).

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Table 2 Simulated light extraction rates from LEDs of different geometries and dimensions.

Equations (8)

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ϕ c = arccos ( cos γ c sin γ ) = arccos ( 1 1 / n 2 sin γ ) = arccos ( n 2 1 n ' sin γ ' )
ϕ = arcsin ( R sin ϕ c r ) = arcsin ( R c r )
ϖ ' = exp ( α d / cos γ ' )
Φ s i d e w a l l c u b o i d = γ 2 γ 3 ϖ ' T 0 r ( 8 ϕ c 2 π ) 2 π r ' d r ' ( 2 π sin γ ' ) d γ '              = 4 r 2 γ 2 γ 3 ϖ ' T ϕ c ( 2 π sin γ ' ) d γ '
Φ s i d e w a l l c i r c u l a r = γ 2 γ 3 ϖ ' T [ 0 R c 2 π r ' d r ' + R c r ( 4 ϕ / 2 π ) 2 π r ' d r ' ] ( 2 π sin γ ' ) d γ '              = 2 r 2 γ 2 γ 3 ϖ ' T [ arcsin ( R c r ) + R c r 1 ( R c r ) 2 ] ( 2 π sin γ ' ) d γ '
T = 1 0.5 × { [ n ' cos γ ' n 1 ( n ' sin γ ' / n ) 2 n ' cos γ ' + n 1 ( n ' sin γ ' / n ) 2 ] 2 + [ n ' 1 ( n ' sin γ ' / n ) 2 n cos γ ' n ' 1 ( n ' sin γ ' / n ) 2 + n cos γ ' ] 2 }
γ 2 = arcsin n 2 1 n '
γ 3 = arcsin n n '

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