Abstract

The improvement of light extraction efficiency of InGaN light-emitting diodes (LEDs) using microsphere arrays with various refractive indices was analyzed. Finite-difference time-domain (FDTD) simulations show that the use of microsphere (d<sub>microsphere</sub> = 500$ nm) arrays with refractive indices of 1.8 and 2.5 led to increase in light extraction efficiency of InGaN LEDs by 1.9 times and 2.2 times, respectively. The enhancement in light extraction efficiency is attributed to the decrease in the Fresnel reflection and increase in effective photon escape cone due to graded refractive index and curvature formed between microsphere and free space. The maximum enhancement of light extraction efficiency of InGaN quantum well LEDs was achieved by employing the refractive index matched anatase-TiO<sub>2</sub> microsphere arrays. The effects of microsphere diameters on the light extraction efficiency were also investigated and 2.4 times enhancement was achieved by employing 400-nm refractive index matched TiO<sub>2</sub> sphere arrays.

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  1. M. H. Crawford, "LEDs for solid-state lighting: Performance challenges and recent advances," IEEE J. Sel. Topics Quantum Electron. 15, 1028-1040 (2009).
  2. Y. K. Ee, J. M. Biser, W. J. Cao, H. M. Chan, R. P. Vinci, N. Tansu, "Metalorganic vapor phase epitaxy of III-nitride light-emitting diodes on nanopatterned AGOG sapphire substrate by abbreviated growth mode," IEEE J. Sel. Topics Quantum Electron. 15, 1066-1072 (2009).
  3. N. F. Gardner, G. O. Muller, Y. C. Shen, G. Chen, S. Watanabe, W. Gotz, M. R. Krames, "Blue-emitting InGaN-GaN double-heterostructure light emitting diodes reaching maximum quantum efficiency above 200 A/cm2," Appl. Phys. Lett. 91, 243506 (2007).
  4. H. Zhao, J. Zhang, G. Liu, N. Tansu, "Surface plasmon dispersion engineering via double-metallic Au/Ag layers for III-nitride based light emitting diodes," Appl. Phys. Lett. 98, 151115 (2011).
  5. X. Li, S. G. Bishop, J. J. Coleman, "GaN epitaxial lateral overgrowth and optical characterization," Appl. Phys. Lett. 73, 1179-1181 (1998).
  6. I. H. Brown, P. Blood, P. M. Smowton, J. D. Thomson, S. M. Olaizola, A. M. Fox, P. J. Parbrook, W. W. Chow, "Time evolution of the screening of piezoelectric fields in InGaN quantum wells," IEEE J. Quantum Electron. 42, 1202-1208 (2006).
  7. J. H. Ryou, P. D. Yoder, J. Liu, Z. Lochner, H. Kim, S. Choi, H. J. Kim, R. D. Dupuis, "Control of quantum-confined stark effect in InGaN-based quantum wells," IEEE J. Sel. Topics Quantum Electron. 15, 1080-1091 (2009).
  8. X. Li, H. Y. Liu, X. Ni, U. Ozgur, H. Morkoc, "Effect of carrier spillover and Auger recombination on the efficiency droop in InGaN-based blue LEDs," Superlattices and Microstructures 47, 118-122 (2010).
  9. B. N. Pantha, I. Feng, K. Aryal, J. Li, J. Y. Lin, H. X. Jiang, "Erbium-doped AlInGaN alloys as high-temperature thermoelectric materials," Appl. Phys. Express 4, 051001 (2011).
  10. J. Zhang, H. Tong, G. Liu, J. A. Herbsommer, G. S. Huang, N. Tansu, "Characterizations of seebeck coefficients and thermoelectric figures of merit for AlInN alloys with various in-contents," J. Appl. Phys. 109, 053706-1-053706-6 (2011).
  11. R. M. Farrell, D. F. Feezell, M. C. Schmidt, D. A. Haeger, K. M. Kelchner, K. Iso, H. Yamada, M. Saito, K. Fujito, D. A. Cohen, J. S. Speck, S. P. DenBaars, S. Nakamura, "Continuous-wave operation of AlGaN-cladding-free nonpolar m-plane InGaN/GaN laser diodes," Jpn. J. Appl. Phys. 46, L761-L763 (2007).
  12. M. Kneissl, "Continuous-wave operation of ultraviolet InGaN/InAlGaN multiple-quantum-well laser diodes," Appl. Phys. Lett. 82, 2386-2388 (2003).
  13. R. Dahal, B. Pantha, J. Li, J. Y. Lin, H. X. Jiang, "InGaN/GaN multiple quantum well solar cells with long operating wavelengths," Appl. Phys. Lett. 94, 063505-1-063505-3 (2009).
  14. A. I. Zhmakin, "Enhancement of light extraction from light emitting diodes," Phys. Rep. 498, 189-241 (2011).
  15. H. Zhao, G. Y. Liu, J. Zhang, J. D. Poplawsky, V. Dierolf, N. Tansu, "Approaches for high internal quantum efficiency green InGaN light-emitting diodes with large overlap quantum wells," Opt. Express 19, A991-A1007 (2011).
  16. R. A. Arif, Y. K. Ee, N. Tansu, "Polarization engineering via staggered InGaN quantum wells for radiative efficiency enhancement of light emitting diodes," Appl. Phys. Lett. 91, 091110 (2007).
  17. S. H. Park, D. Ahn, J. W. Kim, "High-efficiency staggered 530 nm InGaN/InGaN/GaN quantum-well light-emitting diodes," Appl. Phys. Lett. 94, 041109-1-041109-3 (2009).
  18. C. T. Liao, M. C. Tsai, B. T. Liou, S. H. Yen, Y. K. Kuo, "Improvement in output power of a 460 nm InGaN light-emitting diode using staggered quantum well," J. Appl. Phys. 108, 063107 (2010).
  19. U. Ozgur, H. Liu, X. Li, H. Morkoc, "GaN-based light-emitting diodes: Efficiency at high injection levels," Proc. IEEE 98, 1180-1196 (2010).
  20. C. C. Kao, "Light-output enhancement of nano-roughened GaN laser lift-off light-emitting diodes formed by ICP dry etching," IEEE Photon. Techno. Lett. 19, 849-851 (2007).
  21. C. Huh, K. S. Lee, E. J. Kang, S. J. Park, "Improved light-output and electrical performance of InGaN-based, light-emitting diode by microroughening of the p-GaN surface," J. Appl. Phys. 93, 9383-9385 (2003).
  22. T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, S. Nakamura, "Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening," Appl. Phys. Lett. 84, 855-857 (2004).
  23. C. F. Lin, Z. H. Yang, J. H. Zheng, J. H. Dai, "Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall," IEEE Photonic Tech. L. 17, 2038-2040 (2005).
  24. H. W. Huang, "Enhanced light output of an InGaN/GaN light emitting diode with a nano-roughened p-GaN surface," Nanotechnol. 16, 1844-1848 (2005).
  25. H. W. Choi, "GaN micro-light-emitting diode arrays with monolithically integrated sapphire microlenses," Appl. Phys. Lett. 84, 2253-2255 (2004).
  26. J. S. Lee, J. Lee, S. Kim, H. Jeon, "Fabrication of reflective GaN mesa sidewalls for the application to high extraction efficiency LEDs," Phys. Status Solid. (c) 4, 2625-2628 (2007).
  27. J. Q. Xi, H. Luo, A. J. Pasquale, J. K. Kim, E. F. Schubert, "Enhanced light extraction in GaInN light-emitting diode with pyramid reflector," IEEE Photon. Technol. Lett. 18, 2347-2349 (2006).
  28. E. Matioli, "High extraction efficiency GaN-based photonic-crystal light-emitting diodes: Comparison of extraction lengths between surface and embedded photonic crystals," Appl. Phys. Express 3, (2010).
  29. J. J. Wierer, A. David, M. M. Megens, "III-nitride photonic-crystal light-emitting diodes with high extraction efficiency," Nat. Photon. 3, 163-169 (2009).
  30. J. Jewell, "Double embedded photonic crystals for extraction of guided light in light-emitting diodes," Appl. Phys. Lett. 100, (2012) Art. 171105.
  31. C. Wiesmann, K. Bergenek, N. Linder, U. T. Schwarz, "Photonic crystal LEDs—Designing light extraction," Laser Photon. Rev. 3, 262-286 (2009).
  32. M. Fujita, S. Takahashi, Y. Tanaka, T. Asano, S. Noda, "Simultaneous inhibition and redistribution of spontaneous light emission in photonic crystals," Science 308, 1296-1298 (2005).
  33. J. Q. Xi, "Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection," Nat. Photon. 1, 176-179 (2007).
  34. S. Chhajed, W. Lee, J. Cho, E. F. Schubert, J. K. Kim, "Strong light extraction enhancement in GaInN light-emitting diodes by using self-organized nanoscale patterning of p-type GaN," Appl. Phys. Lett. 98, 071102 (2011).
  35. P. Zhao, H. Zhao, "Analysis of light extraction efficiency enhancement for thin-film-flip-chip InGaN quantum wells light-emitting diodes with GaN micro-domes," Opt. Express 20, A765-A776 (2012).
  36. P. Zhao, L. Han, M. R. McGoogan, H. Zhao, "Analysis of TM mode light extraction efficiency enhancement for deep ultraviolet AlGaN quantum wells light-emitting diodes with III-nitride micro-domes," Opt. Mater. Express 2, 1397-1406 (2012).
  37. M. Ma, "Strong light-extraction enhancement in GaInN light-emitting diodes patterned with TiO2 micro-pillars with tapered sidewalls," Appl. Phys. Lett. 101, 141105 (2012).
  38. Y. K. Ee, P. Kumnorkaew, R. A. Arif, J. F. Gilchrist, N. Tansu, "Enhancement of light extraction efficiency of InGaN quantum wells light emitting diodes using SiO2/polystyrene microlens arrays," Appl. Phys. Lett. 91, 221107-1-221107-3 (2007).
  39. Y. K. Ee, P. Kumnorkaew, R. A. Arif, H. Tong, H. Zhao, J. F. Gilchrist, N. Tansu, "Optimization of light extraction efficiency of III-nitride LEDs with self-assembled colloidal-based microlenses," IEEE J. Sel. Topics Quantum Electron. 15, 1218-1225 (2009).
  40. P. Kumnorkaew, Y. K. Ee, N. Tansu, J. F. Gilchrist, "Investigation of the deposition of microsphere monolayers for fabrication of microlens arrays," Langmuir 24, 12150-12157 (2008).
  41. X. H. Li, R. Song, Y. K. Ee, P. Kumnorkaew, J. F. Gilchrist, N. Tansu, "Light extraction efficiency and radiation patterns of III-nitride light emitting diodes with colloidal microlens arrays with various aspect ratios," IEEE Photon. J. 3, 489-499 (2011).
  42. Y. K. Ee, P. Kumnorkaew, R. A. Arif, H. Tong, J. F. Gilchrist, N. Tansu, "Light extraction efficiency enhancement of InGaN quantum wells light-emitting diodes with polydimethylsiloxane concave microstructures," Opt. Express 17, 13747-13757 (2009).
  43. W. H. Koo, W. Youn, P. F. Zhu, X. H. Li, N. Tansu, F. So, "Light extraction of organic light emitting diodes using defective hexagonal-close-packed array," Adv. Funct. Mater. 22, 3454-3459 (2012).

2012

J. Jewell, "Double embedded photonic crystals for extraction of guided light in light-emitting diodes," Appl. Phys. Lett. 100, (2012) Art. 171105.

M. Ma, "Strong light-extraction enhancement in GaInN light-emitting diodes patterned with TiO2 micro-pillars with tapered sidewalls," Appl. Phys. Lett. 101, 141105 (2012).

W. H. Koo, W. Youn, P. F. Zhu, X. H. Li, N. Tansu, F. So, "Light extraction of organic light emitting diodes using defective hexagonal-close-packed array," Adv. Funct. Mater. 22, 3454-3459 (2012).

P. Zhao, H. Zhao, "Analysis of light extraction efficiency enhancement for thin-film-flip-chip InGaN quantum wells light-emitting diodes with GaN micro-domes," Opt. Express 20, A765-A776 (2012).

P. Zhao, L. Han, M. R. McGoogan, H. Zhao, "Analysis of TM mode light extraction efficiency enhancement for deep ultraviolet AlGaN quantum wells light-emitting diodes with III-nitride micro-domes," Opt. Mater. Express 2, 1397-1406 (2012).

2011

A. I. Zhmakin, "Enhancement of light extraction from light emitting diodes," Phys. Rep. 498, 189-241 (2011).

X. H. Li, R. Song, Y. K. Ee, P. Kumnorkaew, J. F. Gilchrist, N. Tansu, "Light extraction efficiency and radiation patterns of III-nitride light emitting diodes with colloidal microlens arrays with various aspect ratios," IEEE Photon. J. 3, 489-499 (2011).

H. Zhao, G. Y. Liu, J. Zhang, J. D. Poplawsky, V. Dierolf, N. Tansu, "Approaches for high internal quantum efficiency green InGaN light-emitting diodes with large overlap quantum wells," Opt. Express 19, A991-A1007 (2011).

B. N. Pantha, I. Feng, K. Aryal, J. Li, J. Y. Lin, H. X. Jiang, "Erbium-doped AlInGaN alloys as high-temperature thermoelectric materials," Appl. Phys. Express 4, 051001 (2011).

J. Zhang, H. Tong, G. Liu, J. A. Herbsommer, G. S. Huang, N. Tansu, "Characterizations of seebeck coefficients and thermoelectric figures of merit for AlInN alloys with various in-contents," J. Appl. Phys. 109, 053706-1-053706-6 (2011).

S. Chhajed, W. Lee, J. Cho, E. F. Schubert, J. K. Kim, "Strong light extraction enhancement in GaInN light-emitting diodes by using self-organized nanoscale patterning of p-type GaN," Appl. Phys. Lett. 98, 071102 (2011).

H. Zhao, J. Zhang, G. Liu, N. Tansu, "Surface plasmon dispersion engineering via double-metallic Au/Ag layers for III-nitride based light emitting diodes," Appl. Phys. Lett. 98, 151115 (2011).

2010

X. Li, H. Y. Liu, X. Ni, U. Ozgur, H. Morkoc, "Effect of carrier spillover and Auger recombination on the efficiency droop in InGaN-based blue LEDs," Superlattices and Microstructures 47, 118-122 (2010).

E. Matioli, "High extraction efficiency GaN-based photonic-crystal light-emitting diodes: Comparison of extraction lengths between surface and embedded photonic crystals," Appl. Phys. Express 3, (2010).

C. T. Liao, M. C. Tsai, B. T. Liou, S. H. Yen, Y. K. Kuo, "Improvement in output power of a 460 nm InGaN light-emitting diode using staggered quantum well," J. Appl. Phys. 108, 063107 (2010).

U. Ozgur, H. Liu, X. Li, H. Morkoc, "GaN-based light-emitting diodes: Efficiency at high injection levels," Proc. IEEE 98, 1180-1196 (2010).

2009

S. H. Park, D. Ahn, J. W. Kim, "High-efficiency staggered 530 nm InGaN/InGaN/GaN quantum-well light-emitting diodes," Appl. Phys. Lett. 94, 041109-1-041109-3 (2009).

J. J. Wierer, A. David, M. M. Megens, "III-nitride photonic-crystal light-emitting diodes with high extraction efficiency," Nat. Photon. 3, 163-169 (2009).

C. Wiesmann, K. Bergenek, N. Linder, U. T. Schwarz, "Photonic crystal LEDs—Designing light extraction," Laser Photon. Rev. 3, 262-286 (2009).

R. Dahal, B. Pantha, J. Li, J. Y. Lin, H. X. Jiang, "InGaN/GaN multiple quantum well solar cells with long operating wavelengths," Appl. Phys. Lett. 94, 063505-1-063505-3 (2009).

J. H. Ryou, P. D. Yoder, J. Liu, Z. Lochner, H. Kim, S. Choi, H. J. Kim, R. D. Dupuis, "Control of quantum-confined stark effect in InGaN-based quantum wells," IEEE J. Sel. Topics Quantum Electron. 15, 1080-1091 (2009).

M. H. Crawford, "LEDs for solid-state lighting: Performance challenges and recent advances," IEEE J. Sel. Topics Quantum Electron. 15, 1028-1040 (2009).

Y. K. Ee, J. M. Biser, W. J. Cao, H. M. Chan, R. P. Vinci, N. Tansu, "Metalorganic vapor phase epitaxy of III-nitride light-emitting diodes on nanopatterned AGOG sapphire substrate by abbreviated growth mode," IEEE J. Sel. Topics Quantum Electron. 15, 1066-1072 (2009).

Y. K. Ee, P. Kumnorkaew, R. A. Arif, H. Tong, H. Zhao, J. F. Gilchrist, N. Tansu, "Optimization of light extraction efficiency of III-nitride LEDs with self-assembled colloidal-based microlenses," IEEE J. Sel. Topics Quantum Electron. 15, 1218-1225 (2009).

Y. K. Ee, P. Kumnorkaew, R. A. Arif, H. Tong, J. F. Gilchrist, N. Tansu, "Light extraction efficiency enhancement of InGaN quantum wells light-emitting diodes with polydimethylsiloxane concave microstructures," Opt. Express 17, 13747-13757 (2009).

2008

P. Kumnorkaew, Y. K. Ee, N. Tansu, J. F. Gilchrist, "Investigation of the deposition of microsphere monolayers for fabrication of microlens arrays," Langmuir 24, 12150-12157 (2008).

2007

N. F. Gardner, G. O. Muller, Y. C. Shen, G. Chen, S. Watanabe, W. Gotz, M. R. Krames, "Blue-emitting InGaN-GaN double-heterostructure light emitting diodes reaching maximum quantum efficiency above 200 A/cm2," Appl. Phys. Lett. 91, 243506 (2007).

Y. K. Ee, P. Kumnorkaew, R. A. Arif, J. F. Gilchrist, N. Tansu, "Enhancement of light extraction efficiency of InGaN quantum wells light emitting diodes using SiO2/polystyrene microlens arrays," Appl. Phys. Lett. 91, 221107-1-221107-3 (2007).

R. M. Farrell, D. F. Feezell, M. C. Schmidt, D. A. Haeger, K. M. Kelchner, K. Iso, H. Yamada, M. Saito, K. Fujito, D. A. Cohen, J. S. Speck, S. P. DenBaars, S. Nakamura, "Continuous-wave operation of AlGaN-cladding-free nonpolar m-plane InGaN/GaN laser diodes," Jpn. J. Appl. Phys. 46, L761-L763 (2007).

J. Q. Xi, "Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection," Nat. Photon. 1, 176-179 (2007).

J. S. Lee, J. Lee, S. Kim, H. Jeon, "Fabrication of reflective GaN mesa sidewalls for the application to high extraction efficiency LEDs," Phys. Status Solid. (c) 4, 2625-2628 (2007).

R. A. Arif, Y. K. Ee, N. Tansu, "Polarization engineering via staggered InGaN quantum wells for radiative efficiency enhancement of light emitting diodes," Appl. Phys. Lett. 91, 091110 (2007).

C. C. Kao, "Light-output enhancement of nano-roughened GaN laser lift-off light-emitting diodes formed by ICP dry etching," IEEE Photon. Techno. Lett. 19, 849-851 (2007).

2006

J. Q. Xi, H. Luo, A. J. Pasquale, J. K. Kim, E. F. Schubert, "Enhanced light extraction in GaInN light-emitting diode with pyramid reflector," IEEE Photon. Technol. Lett. 18, 2347-2349 (2006).

I. H. Brown, P. Blood, P. M. Smowton, J. D. Thomson, S. M. Olaizola, A. M. Fox, P. J. Parbrook, W. W. Chow, "Time evolution of the screening of piezoelectric fields in InGaN quantum wells," IEEE J. Quantum Electron. 42, 1202-1208 (2006).

2005

M. Fujita, S. Takahashi, Y. Tanaka, T. Asano, S. Noda, "Simultaneous inhibition and redistribution of spontaneous light emission in photonic crystals," Science 308, 1296-1298 (2005).

C. F. Lin, Z. H. Yang, J. H. Zheng, J. H. Dai, "Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall," IEEE Photonic Tech. L. 17, 2038-2040 (2005).

H. W. Huang, "Enhanced light output of an InGaN/GaN light emitting diode with a nano-roughened p-GaN surface," Nanotechnol. 16, 1844-1848 (2005).

2004

H. W. Choi, "GaN micro-light-emitting diode arrays with monolithically integrated sapphire microlenses," Appl. Phys. Lett. 84, 2253-2255 (2004).

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

2003

C. Huh, K. S. Lee, E. J. Kang, S. J. Park, "Improved light-output and electrical performance of InGaN-based, light-emitting diode by microroughening of the p-GaN surface," J. Appl. Phys. 93, 9383-9385 (2003).

M. Kneissl, "Continuous-wave operation of ultraviolet InGaN/InAlGaN multiple-quantum-well laser diodes," Appl. Phys. Lett. 82, 2386-2388 (2003).

1998

X. Li, S. G. Bishop, J. J. Coleman, "GaN epitaxial lateral overgrowth and optical characterization," Appl. Phys. Lett. 73, 1179-1181 (1998).

Adv. Funct. Mater.

W. H. Koo, W. Youn, P. F. Zhu, X. H. Li, N. Tansu, F. So, "Light extraction of organic light emitting diodes using defective hexagonal-close-packed array," Adv. Funct. Mater. 22, 3454-3459 (2012).

Appl. Phys. Express

B. N. Pantha, I. Feng, K. Aryal, J. Li, J. Y. Lin, H. X. Jiang, "Erbium-doped AlInGaN alloys as high-temperature thermoelectric materials," Appl. Phys. Express 4, 051001 (2011).

E. Matioli, "High extraction efficiency GaN-based photonic-crystal light-emitting diodes: Comparison of extraction lengths between surface and embedded photonic crystals," Appl. Phys. Express 3, (2010).

Appl. Phys. Lett.

H. W. Choi, "GaN micro-light-emitting diode arrays with monolithically integrated sapphire microlenses," Appl. Phys. Lett. 84, 2253-2255 (2004).

J. Jewell, "Double embedded photonic crystals for extraction of guided light in light-emitting diodes," Appl. Phys. Lett. 100, (2012) Art. 171105.

R. A. Arif, Y. K. Ee, N. Tansu, "Polarization engineering via staggered InGaN quantum wells for radiative efficiency enhancement of light emitting diodes," Appl. Phys. Lett. 91, 091110 (2007).

S. H. Park, D. Ahn, J. W. Kim, "High-efficiency staggered 530 nm InGaN/InGaN/GaN quantum-well light-emitting diodes," Appl. Phys. Lett. 94, 041109-1-041109-3 (2009).

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

S. Chhajed, W. Lee, J. Cho, E. F. Schubert, J. K. Kim, "Strong light extraction enhancement in GaInN light-emitting diodes by using self-organized nanoscale patterning of p-type GaN," Appl. Phys. Lett. 98, 071102 (2011).

N. F. Gardner, G. O. Muller, Y. C. Shen, G. Chen, S. Watanabe, W. Gotz, M. R. Krames, "Blue-emitting InGaN-GaN double-heterostructure light emitting diodes reaching maximum quantum efficiency above 200 A/cm2," Appl. Phys. Lett. 91, 243506 (2007).

H. Zhao, J. Zhang, G. Liu, N. Tansu, "Surface plasmon dispersion engineering via double-metallic Au/Ag layers for III-nitride based light emitting diodes," Appl. Phys. Lett. 98, 151115 (2011).

X. Li, S. G. Bishop, J. J. Coleman, "GaN epitaxial lateral overgrowth and optical characterization," Appl. Phys. Lett. 73, 1179-1181 (1998).

M. Ma, "Strong light-extraction enhancement in GaInN light-emitting diodes patterned with TiO2 micro-pillars with tapered sidewalls," Appl. Phys. Lett. 101, 141105 (2012).

Y. K. Ee, P. Kumnorkaew, R. A. Arif, J. F. Gilchrist, N. Tansu, "Enhancement of light extraction efficiency of InGaN quantum wells light emitting diodes using SiO2/polystyrene microlens arrays," Appl. Phys. Lett. 91, 221107-1-221107-3 (2007).

M. Kneissl, "Continuous-wave operation of ultraviolet InGaN/InAlGaN multiple-quantum-well laser diodes," Appl. Phys. Lett. 82, 2386-2388 (2003).

R. Dahal, B. Pantha, J. Li, J. Y. Lin, H. X. Jiang, "InGaN/GaN multiple quantum well solar cells with long operating wavelengths," Appl. Phys. Lett. 94, 063505-1-063505-3 (2009).

IEEE J. Quantum Electron.

I. H. Brown, P. Blood, P. M. Smowton, J. D. Thomson, S. M. Olaizola, A. M. Fox, P. J. Parbrook, W. W. Chow, "Time evolution of the screening of piezoelectric fields in InGaN quantum wells," IEEE J. Quantum Electron. 42, 1202-1208 (2006).

IEEE J. Sel. Topics Quantum Electron.

J. H. Ryou, P. D. Yoder, J. Liu, Z. Lochner, H. Kim, S. Choi, H. J. Kim, R. D. Dupuis, "Control of quantum-confined stark effect in InGaN-based quantum wells," IEEE J. Sel. Topics Quantum Electron. 15, 1080-1091 (2009).

M. H. Crawford, "LEDs for solid-state lighting: Performance challenges and recent advances," IEEE J. Sel. Topics Quantum Electron. 15, 1028-1040 (2009).

Y. K. Ee, J. M. Biser, W. J. Cao, H. M. Chan, R. P. Vinci, N. Tansu, "Metalorganic vapor phase epitaxy of III-nitride light-emitting diodes on nanopatterned AGOG sapphire substrate by abbreviated growth mode," IEEE J. Sel. Topics Quantum Electron. 15, 1066-1072 (2009).

Y. K. Ee, P. Kumnorkaew, R. A. Arif, H. Tong, H. Zhao, J. F. Gilchrist, N. Tansu, "Optimization of light extraction efficiency of III-nitride LEDs with self-assembled colloidal-based microlenses," IEEE J. Sel. Topics Quantum Electron. 15, 1218-1225 (2009).

IEEE Photon. J.

X. H. Li, R. Song, Y. K. Ee, P. Kumnorkaew, J. F. Gilchrist, N. Tansu, "Light extraction efficiency and radiation patterns of III-nitride light emitting diodes with colloidal microlens arrays with various aspect ratios," IEEE Photon. J. 3, 489-499 (2011).

IEEE Photon. Techno. Lett.

C. C. Kao, "Light-output enhancement of nano-roughened GaN laser lift-off light-emitting diodes formed by ICP dry etching," IEEE Photon. Techno. Lett. 19, 849-851 (2007).

IEEE Photon. Technol. Lett.

J. Q. Xi, H. Luo, A. J. Pasquale, J. K. Kim, E. F. Schubert, "Enhanced light extraction in GaInN light-emitting diode with pyramid reflector," IEEE Photon. Technol. Lett. 18, 2347-2349 (2006).

IEEE Photonic Tech. L.

C. F. Lin, Z. H. Yang, J. H. Zheng, J. H. Dai, "Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall," IEEE Photonic Tech. L. 17, 2038-2040 (2005).

J. Appl. Phys.

C. Huh, K. S. Lee, E. J. Kang, S. J. Park, "Improved light-output and electrical performance of InGaN-based, light-emitting diode by microroughening of the p-GaN surface," J. Appl. Phys. 93, 9383-9385 (2003).

C. T. Liao, M. C. Tsai, B. T. Liou, S. H. Yen, Y. K. Kuo, "Improvement in output power of a 460 nm InGaN light-emitting diode using staggered quantum well," J. Appl. Phys. 108, 063107 (2010).

J. Zhang, H. Tong, G. Liu, J. A. Herbsommer, G. S. Huang, N. Tansu, "Characterizations of seebeck coefficients and thermoelectric figures of merit for AlInN alloys with various in-contents," J. Appl. Phys. 109, 053706-1-053706-6 (2011).

Jpn. J. Appl. Phys.

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