Abstract

We demonstrate novel method for improving light extraction efficiency for n-side-up vertical InGaN/GaN light-emitting diodes (V-LEDs) using MgO nano-pyramids and ZnO refractive-index modulation layer. The MgO nano-pyramids structure is successfully fabricated on n-GaN/ZnO surface using electron-beam evaporation. The light output power of n-GaN/ZnO/MgO V-LEDs is enhanced by 49% compare to that of n-GaN V-LEDs. The angular-dependent far-field emission shows the significant increase of side emission for the n-GaN/ZnO/MgO V-LEDs due to the increase of critical angle for total internal reflection as well as the roughened surface by MgO pyramids structure. These experimental results indicate the critical role of surface texturing in improving the light extraction efficiency of the V-LEDs for solid-state lighting.

© 2010 OSA

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  3. A. Hangleiter, D. Fuhrmann, M. Grewe, F. Hitzel, G. Klewer, S. Lahmann, C. Netzel, N. Riedel, and U. Rossow, “Towards understanding the emission efficiency of nitride quantum wells,” Phys. Status Solidi A 201(12), 2808–2813 (2004).
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  4. D. Fuhrmann, C. Netzel, U. Rossow, A. Hangleiter, G. Ade, and P. Hinze, “Optimization scheme for the quantum efficiency of GaInN-based green-light-emitting diodes,” Appl. Phys. Lett. 88(7), 071105 (2006).
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    [CrossRef]
  7. C. H. Kuo, H. C. Feng, C. W. Kuo, C. M. Chen, L. W. Wu, and G. C. Chi, “Nitride-based near-ultraviolet light emitting diodes with meshed p‐GaN,” Appl. Phys. Lett. 90(14), 142115 (2007).
    [CrossRef]
  8. J. J. Wierer, A. David, and M. Megens, “III-nitride photonic-crystal light-emitting diodes with high extraction efficiency,” Nat. Photonics 3(3), 163–169 (2009).
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  9. M.-K. Kwon, J.-Y. Kim, I.-K. Park, K. S. Kim, G.-Y. Jung, S.-J. Park, J. W. Kim, and Y. C. Kim, “Enhanced emission efficiency of GaN/InGaN multiple quantum well light-emitting diode with an embedded photonic crystal,” Appl. Phys. Lett. 92(25), 251110 (2008).
    [CrossRef]
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    [CrossRef]
  11. H. Jia, L. Guo, W. Wang, and H. Chen, “Recent Progress in GaN-Based Light-Emitting Diodes,” Adv. Mater. 21(45), 4641–4646 (2009).
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  12. W. K. Wang, S. H. Huang, K. S. Wen, D. S. Wuu, and R. H. Horng, “Fabrication and efficiency improvement of micropillar InGaN/Cu light-emitting diodes with vertical electrodes,” Appl. Phys. Lett. 88(18), 181113 (2006).
    [CrossRef]
  13. S.-H. Huang, R.-H. Horng, S.-L. Li, K.-W. Yen, D.-S. Wuu, C.-K. Lin, and H. Liu, “Thermally Stable Mirror Structures for Vertical-Conducting GaN/Mirror/Si Light-Emitting Diodes,” IEEE Photon. Technol. Lett. 19(23), 1913–1915 (2007).
    [CrossRef]
  14. X.-M. Zhang, M.-Y. Lu, Y. Zhang, L.-J. Chen, and Z. L. Wang, “Fabrication of a High-Brightness Blue-Light-Emitting Diode Using a ZnO-Nanowire Array Grown on p-GaN Thin Film,” Adv. Mater. 21(27), 2767–2770 (2009).
    [CrossRef]
  15. M.-C. Jeong, B.-Y. Oh, M.-H. Ham, S.-W. Lee, and J.-M. Myoung, “ZnO-nanowire-inserted GaN/ZnO heterojunction light-emitting diodes,” Small 3(4), 568–572 (2007).
    [CrossRef] [PubMed]
  16. J.-L. Lee, M. H. Weber, J. K. Kim, and K. G. Lynn, “Positron annihilation study of Pd contacts on impurity-doped GaN,” Appl. Phys. Lett. 78(26), 4142 (2001).
    [CrossRef]
  17. C. Noguera, “Polar oxide surfaces,” J. Phys. Condens. Matter 12(31), 201 (2000).
    [CrossRef]
  18. M. Kästner and B. Voigtlander, “Kinetically Self-Limiting Growth of Ge Islands on Si(001),” Phys. Rev. Lett. 82(13), 2745–2748 (1999).
    [CrossRef]
  19. J. Goniakowski, F. Finocchi, and C. Noguera, “Polarity of oxide surfaces and nanostructures,” Rep. Prog. Phys. 71(1), 016501 (2008).
    [CrossRef]
  20. D. Wolf, “Reconstruction of NaCl surfaces from a dipolar solution to the Madelung problem,” Phys. Rev. Lett. 68(22), 3315–3318 (1992).
    [CrossRef] [PubMed]
  21. V. E. Henrich, “Thermal faceting of (110) and (111) surfaces of MgO,” Surf. Sci. 57(1), 385–392 (1976).
    [CrossRef]
  22. X.-S. Fang, C.-H. Ye, L.-D. Zhang, J.-X. Zhang, J.-W. Zhao, and P. Yan, “Direct observation of the growth process of MgO nanoflowers by a simple chemical route,” Small 1(4), 422–428 (2005).
    [CrossRef]
  23. Y.-J. Lin, C.-L. Tsai, Y.-M. Lu, and C.-J. Liu, “Optical and electrical properties of undoped ZnO films,” J. Appl. Phys. 99(9), 093501 (2006).
    [CrossRef]

2009 (5)

S. Noda and M. Fujita, “Light-emitting diodes: Photonic crystal efficiency boost,” Nat. Photonics 3(3), 129–130 (2009).
[CrossRef]

S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
[CrossRef]

J. J. Wierer, A. David, and M. Megens, “III-nitride photonic-crystal light-emitting diodes with high extraction efficiency,” Nat. Photonics 3(3), 163–169 (2009).
[CrossRef]

H. Jia, L. Guo, W. Wang, and H. Chen, “Recent Progress in GaN-Based Light-Emitting Diodes,” Adv. Mater. 21(45), 4641–4646 (2009).
[CrossRef]

X.-M. Zhang, M.-Y. Lu, Y. Zhang, L.-J. Chen, and Z. L. Wang, “Fabrication of a High-Brightness Blue-Light-Emitting Diode Using a ZnO-Nanowire Array Grown on p-GaN Thin Film,” Adv. Mater. 21(27), 2767–2770 (2009).
[CrossRef]

2008 (3)

J. Goniakowski, F. Finocchi, and C. Noguera, “Polarity of oxide surfaces and nanostructures,” Rep. Prog. Phys. 71(1), 016501 (2008).
[CrossRef]

M.-K. Kwon, J.-Y. Kim, I.-K. Park, K. S. Kim, G.-Y. Jung, S.-J. Park, J. W. Kim, and Y. C. Kim, “Enhanced emission efficiency of GaN/InGaN multiple quantum well light-emitting diode with an embedded photonic crystal,” Appl. Phys. Lett. 92(25), 251110 (2008).
[CrossRef]

J. K. Kim, S. Chhajed, M. F. Schubert, E. F. Schubert, A. J. Fischer, M. H. Crawford, J. Cho, H. Kim, and C. Sone, “Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact,” Adv. Mater. 20(4), 801–804 (2008).
[CrossRef]

2007 (3)

C. H. Kuo, H. C. Feng, C. W. Kuo, C. M. Chen, L. W. Wu, and G. C. Chi, “Nitride-based near-ultraviolet light emitting diodes with meshed p‐GaN,” Appl. Phys. Lett. 90(14), 142115 (2007).
[CrossRef]

S.-H. Huang, R.-H. Horng, S.-L. Li, K.-W. Yen, D.-S. Wuu, C.-K. Lin, and H. Liu, “Thermally Stable Mirror Structures for Vertical-Conducting GaN/Mirror/Si Light-Emitting Diodes,” IEEE Photon. Technol. Lett. 19(23), 1913–1915 (2007).
[CrossRef]

M.-C. Jeong, B.-Y. Oh, M.-H. Ham, S.-W. Lee, and J.-M. Myoung, “ZnO-nanowire-inserted GaN/ZnO heterojunction light-emitting diodes,” Small 3(4), 568–572 (2007).
[CrossRef] [PubMed]

2006 (3)

W. K. Wang, S. H. Huang, K. S. Wen, D. S. Wuu, and R. H. Horng, “Fabrication and efficiency improvement of micropillar InGaN/Cu light-emitting diodes with vertical electrodes,” Appl. Phys. Lett. 88(18), 181113 (2006).
[CrossRef]

D. Fuhrmann, C. Netzel, U. Rossow, A. Hangleiter, G. Ade, and P. Hinze, “Optimization scheme for the quantum efficiency of GaInN-based green-light-emitting diodes,” Appl. Phys. Lett. 88(7), 071105 (2006).
[CrossRef]

Y.-J. Lin, C.-L. Tsai, Y.-M. Lu, and C.-J. Liu, “Optical and electrical properties of undoped ZnO films,” J. Appl. Phys. 99(9), 093501 (2006).
[CrossRef]

2005 (1)

X.-S. Fang, C.-H. Ye, L.-D. Zhang, J.-X. Zhang, J.-W. Zhao, and P. Yan, “Direct observation of the growth process of MgO nanoflowers by a simple chemical route,” Small 1(4), 422–428 (2005).
[CrossRef]

2004 (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 (2004).
[CrossRef]

A. Hangleiter, D. Fuhrmann, M. Grewe, F. Hitzel, G. Klewer, S. Lahmann, C. Netzel, N. Riedel, and U. Rossow, “Towards understanding the emission efficiency of nitride quantum wells,” Phys. Status Solidi A 201(12), 2808–2813 (2004).
[CrossRef]

2001 (1)

J.-L. Lee, M. H. Weber, J. K. Kim, and K. G. Lynn, “Positron annihilation study of Pd contacts on impurity-doped GaN,” Appl. Phys. Lett. 78(26), 4142 (2001).
[CrossRef]

2000 (1)

C. Noguera, “Polar oxide surfaces,” J. Phys. Condens. Matter 12(31), 201 (2000).
[CrossRef]

1999 (1)

M. Kästner and B. Voigtlander, “Kinetically Self-Limiting Growth of Ge Islands on Si(001),” Phys. Rev. Lett. 82(13), 2745–2748 (1999).
[CrossRef]

1992 (1)

D. Wolf, “Reconstruction of NaCl surfaces from a dipolar solution to the Madelung problem,” Phys. Rev. Lett. 68(22), 3315–3318 (1992).
[CrossRef] [PubMed]

1976 (1)

V. E. Henrich, “Thermal faceting of (110) and (111) surfaces of MgO,” Surf. Sci. 57(1), 385–392 (1976).
[CrossRef]

Ade, G.

D. Fuhrmann, C. Netzel, U. Rossow, A. Hangleiter, G. Ade, and P. Hinze, “Optimization scheme for the quantum efficiency of GaInN-based green-light-emitting diodes,” Appl. Phys. Lett. 88(7), 071105 (2006).
[CrossRef]

Chen, C. M.

C. H. Kuo, H. C. Feng, C. W. Kuo, C. M. Chen, L. W. Wu, and G. C. Chi, “Nitride-based near-ultraviolet light emitting diodes with meshed p‐GaN,” Appl. Phys. Lett. 90(14), 142115 (2007).
[CrossRef]

Chen, H.

H. Jia, L. Guo, W. Wang, and H. Chen, “Recent Progress in GaN-Based Light-Emitting Diodes,” Adv. Mater. 21(45), 4641–4646 (2009).
[CrossRef]

Chen, L.-J.

X.-M. Zhang, M.-Y. Lu, Y. Zhang, L.-J. Chen, and Z. L. Wang, “Fabrication of a High-Brightness Blue-Light-Emitting Diode Using a ZnO-Nanowire Array Grown on p-GaN Thin Film,” Adv. Mater. 21(27), 2767–2770 (2009).
[CrossRef]

Chhajed, S.

J. K. Kim, S. Chhajed, M. F. Schubert, E. F. Schubert, A. J. Fischer, M. H. Crawford, J. Cho, H. Kim, and C. Sone, “Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact,” Adv. Mater. 20(4), 801–804 (2008).
[CrossRef]

Chi, G. C.

C. H. Kuo, H. C. Feng, C. W. Kuo, C. M. Chen, L. W. Wu, and G. C. Chi, “Nitride-based near-ultraviolet light emitting diodes with meshed p‐GaN,” Appl. Phys. Lett. 90(14), 142115 (2007).
[CrossRef]

Cho, J.

J. K. Kim, S. Chhajed, M. F. Schubert, E. F. Schubert, A. J. Fischer, M. H. Crawford, J. Cho, H. Kim, and C. Sone, “Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact,” Adv. Mater. 20(4), 801–804 (2008).
[CrossRef]

Crawford, M. H.

J. K. Kim, S. Chhajed, M. F. Schubert, E. F. Schubert, A. J. Fischer, M. H. Crawford, J. Cho, H. Kim, and C. Sone, “Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact,” Adv. Mater. 20(4), 801–804 (2008).
[CrossRef]

David, A.

J. J. Wierer, A. David, and M. Megens, “III-nitride photonic-crystal light-emitting diodes with high extraction efficiency,” Nat. Photonics 3(3), 163–169 (2009).
[CrossRef]

DenBaars, S. P.

S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
[CrossRef]

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 (2004).
[CrossRef]

Fang, X.-S.

X.-S. Fang, C.-H. Ye, L.-D. Zhang, J.-X. Zhang, J.-W. Zhao, and P. Yan, “Direct observation of the growth process of MgO nanoflowers by a simple chemical route,” Small 1(4), 422–428 (2005).
[CrossRef]

Feng, H. C.

C. H. Kuo, H. C. Feng, C. W. Kuo, C. M. Chen, L. W. Wu, and G. C. Chi, “Nitride-based near-ultraviolet light emitting diodes with meshed p‐GaN,” Appl. Phys. Lett. 90(14), 142115 (2007).
[CrossRef]

Finocchi, F.

J. Goniakowski, F. Finocchi, and C. Noguera, “Polarity of oxide surfaces and nanostructures,” Rep. Prog. Phys. 71(1), 016501 (2008).
[CrossRef]

Fischer, A. J.

J. K. Kim, S. Chhajed, M. F. Schubert, E. F. Schubert, A. J. Fischer, M. H. Crawford, J. Cho, H. Kim, and C. Sone, “Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact,” Adv. Mater. 20(4), 801–804 (2008).
[CrossRef]

Fuhrmann, D.

D. Fuhrmann, C. Netzel, U. Rossow, A. Hangleiter, G. Ade, and P. Hinze, “Optimization scheme for the quantum efficiency of GaInN-based green-light-emitting diodes,” Appl. Phys. Lett. 88(7), 071105 (2006).
[CrossRef]

A. Hangleiter, D. Fuhrmann, M. Grewe, F. Hitzel, G. Klewer, S. Lahmann, C. Netzel, N. Riedel, and U. Rossow, “Towards understanding the emission efficiency of nitride quantum wells,” Phys. Status Solidi A 201(12), 2808–2813 (2004).
[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 (2004).
[CrossRef]

Fujita, M.

S. Noda and M. Fujita, “Light-emitting diodes: Photonic crystal efficiency boost,” Nat. Photonics 3(3), 129–130 (2009).
[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 (2004).
[CrossRef]

Goniakowski, J.

J. Goniakowski, F. Finocchi, and C. Noguera, “Polarity of oxide surfaces and nanostructures,” Rep. Prog. Phys. 71(1), 016501 (2008).
[CrossRef]

Grewe, M.

A. Hangleiter, D. Fuhrmann, M. Grewe, F. Hitzel, G. Klewer, S. Lahmann, C. Netzel, N. Riedel, and U. Rossow, “Towards understanding the emission efficiency of nitride quantum wells,” Phys. Status Solidi A 201(12), 2808–2813 (2004).
[CrossRef]

Guo, L.

H. Jia, L. Guo, W. Wang, and H. Chen, “Recent Progress in GaN-Based Light-Emitting Diodes,” Adv. Mater. 21(45), 4641–4646 (2009).
[CrossRef]

Ham, M.-H.

M.-C. Jeong, B.-Y. Oh, M.-H. Ham, S.-W. Lee, and J.-M. Myoung, “ZnO-nanowire-inserted GaN/ZnO heterojunction light-emitting diodes,” Small 3(4), 568–572 (2007).
[CrossRef] [PubMed]

Hangleiter, A.

D. Fuhrmann, C. Netzel, U. Rossow, A. Hangleiter, G. Ade, and P. Hinze, “Optimization scheme for the quantum efficiency of GaInN-based green-light-emitting diodes,” Appl. Phys. Lett. 88(7), 071105 (2006).
[CrossRef]

A. Hangleiter, D. Fuhrmann, M. Grewe, F. Hitzel, G. Klewer, S. Lahmann, C. Netzel, N. Riedel, and U. Rossow, “Towards understanding the emission efficiency of nitride quantum wells,” Phys. Status Solidi A 201(12), 2808–2813 (2004).
[CrossRef]

Henrich, V. E.

V. E. Henrich, “Thermal faceting of (110) and (111) surfaces of MgO,” Surf. Sci. 57(1), 385–392 (1976).
[CrossRef]

Hinze, P.

D. Fuhrmann, C. Netzel, U. Rossow, A. Hangleiter, G. Ade, and P. Hinze, “Optimization scheme for the quantum efficiency of GaInN-based green-light-emitting diodes,” Appl. Phys. Lett. 88(7), 071105 (2006).
[CrossRef]

Hitzel, F.

A. Hangleiter, D. Fuhrmann, M. Grewe, F. Hitzel, G. Klewer, S. Lahmann, C. Netzel, N. Riedel, and U. Rossow, “Towards understanding the emission efficiency of nitride quantum wells,” Phys. Status Solidi A 201(12), 2808–2813 (2004).
[CrossRef]

Horng, R. H.

W. K. Wang, S. H. Huang, K. S. Wen, D. S. Wuu, and R. H. Horng, “Fabrication and efficiency improvement of micropillar InGaN/Cu light-emitting diodes with vertical electrodes,” Appl. Phys. Lett. 88(18), 181113 (2006).
[CrossRef]

Horng, R.-H.

S.-H. Huang, R.-H. Horng, S.-L. Li, K.-W. Yen, D.-S. Wuu, C.-K. Lin, and H. Liu, “Thermally Stable Mirror Structures for Vertical-Conducting GaN/Mirror/Si Light-Emitting Diodes,” IEEE Photon. Technol. Lett. 19(23), 1913–1915 (2007).
[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 (2004).
[CrossRef]

Huang, S. H.

W. K. Wang, S. H. Huang, K. S. Wen, D. S. Wuu, and R. H. Horng, “Fabrication and efficiency improvement of micropillar InGaN/Cu light-emitting diodes with vertical electrodes,” Appl. Phys. Lett. 88(18), 181113 (2006).
[CrossRef]

Huang, S.-H.

S.-H. Huang, R.-H. Horng, S.-L. Li, K.-W. Yen, D.-S. Wuu, C.-K. Lin, and H. Liu, “Thermally Stable Mirror Structures for Vertical-Conducting GaN/Mirror/Si Light-Emitting Diodes,” IEEE Photon. Technol. Lett. 19(23), 1913–1915 (2007).
[CrossRef]

Jeong, M.-C.

M.-C. Jeong, B.-Y. Oh, M.-H. Ham, S.-W. Lee, and J.-M. Myoung, “ZnO-nanowire-inserted GaN/ZnO heterojunction light-emitting diodes,” Small 3(4), 568–572 (2007).
[CrossRef] [PubMed]

Jia, H.

H. Jia, L. Guo, W. Wang, and H. Chen, “Recent Progress in GaN-Based Light-Emitting Diodes,” Adv. Mater. 21(45), 4641–4646 (2009).
[CrossRef]

Jung, G.-Y.

M.-K. Kwon, J.-Y. Kim, I.-K. Park, K. S. Kim, G.-Y. Jung, S.-J. Park, J. W. Kim, and Y. C. Kim, “Enhanced emission efficiency of GaN/InGaN multiple quantum well light-emitting diode with an embedded photonic crystal,” Appl. Phys. Lett. 92(25), 251110 (2008).
[CrossRef]

Kästner, M.

M. Kästner and B. Voigtlander, “Kinetically Self-Limiting Growth of Ge Islands on Si(001),” Phys. Rev. Lett. 82(13), 2745–2748 (1999).
[CrossRef]

Kim, H.

J. K. Kim, S. Chhajed, M. F. Schubert, E. F. Schubert, A. J. Fischer, M. H. Crawford, J. Cho, H. Kim, and C. Sone, “Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact,” Adv. Mater. 20(4), 801–804 (2008).
[CrossRef]

Kim, J. K.

J. K. Kim, S. Chhajed, M. F. Schubert, E. F. Schubert, A. J. Fischer, M. H. Crawford, J. Cho, H. Kim, and C. Sone, “Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact,” Adv. Mater. 20(4), 801–804 (2008).
[CrossRef]

J.-L. Lee, M. H. Weber, J. K. Kim, and K. G. Lynn, “Positron annihilation study of Pd contacts on impurity-doped GaN,” Appl. Phys. Lett. 78(26), 4142 (2001).
[CrossRef]

Kim, J. W.

M.-K. Kwon, J.-Y. Kim, I.-K. Park, K. S. Kim, G.-Y. Jung, S.-J. Park, J. W. Kim, and Y. C. Kim, “Enhanced emission efficiency of GaN/InGaN multiple quantum well light-emitting diode with an embedded photonic crystal,” Appl. Phys. Lett. 92(25), 251110 (2008).
[CrossRef]

Kim, J.-Y.

M.-K. Kwon, J.-Y. Kim, I.-K. Park, K. S. Kim, G.-Y. Jung, S.-J. Park, J. W. Kim, and Y. C. Kim, “Enhanced emission efficiency of GaN/InGaN multiple quantum well light-emitting diode with an embedded photonic crystal,” Appl. Phys. Lett. 92(25), 251110 (2008).
[CrossRef]

Kim, K. S.

M.-K. Kwon, J.-Y. Kim, I.-K. Park, K. S. Kim, G.-Y. Jung, S.-J. Park, J. W. Kim, and Y. C. Kim, “Enhanced emission efficiency of GaN/InGaN multiple quantum well light-emitting diode with an embedded photonic crystal,” Appl. Phys. Lett. 92(25), 251110 (2008).
[CrossRef]

Kim, Y. C.

M.-K. Kwon, J.-Y. Kim, I.-K. Park, K. S. Kim, G.-Y. Jung, S.-J. Park, J. W. Kim, and Y. C. Kim, “Enhanced emission efficiency of GaN/InGaN multiple quantum well light-emitting diode with an embedded photonic crystal,” Appl. Phys. Lett. 92(25), 251110 (2008).
[CrossRef]

Klewer, G.

A. Hangleiter, D. Fuhrmann, M. Grewe, F. Hitzel, G. Klewer, S. Lahmann, C. Netzel, N. Riedel, and U. Rossow, “Towards understanding the emission efficiency of nitride quantum wells,” Phys. Status Solidi A 201(12), 2808–2813 (2004).
[CrossRef]

Kuo, C. H.

C. H. Kuo, H. C. Feng, C. W. Kuo, C. M. Chen, L. W. Wu, and G. C. Chi, “Nitride-based near-ultraviolet light emitting diodes with meshed p‐GaN,” Appl. Phys. Lett. 90(14), 142115 (2007).
[CrossRef]

Kuo, C. W.

C. H. Kuo, H. C. Feng, C. W. Kuo, C. M. Chen, L. W. Wu, and G. C. Chi, “Nitride-based near-ultraviolet light emitting diodes with meshed p‐GaN,” Appl. Phys. Lett. 90(14), 142115 (2007).
[CrossRef]

Kwon, M.-K.

M.-K. Kwon, J.-Y. Kim, I.-K. Park, K. S. Kim, G.-Y. Jung, S.-J. Park, J. W. Kim, and Y. C. Kim, “Enhanced emission efficiency of GaN/InGaN multiple quantum well light-emitting diode with an embedded photonic crystal,” Appl. Phys. Lett. 92(25), 251110 (2008).
[CrossRef]

Lahmann, S.

A. Hangleiter, D. Fuhrmann, M. Grewe, F. Hitzel, G. Klewer, S. Lahmann, C. Netzel, N. Riedel, and U. Rossow, “Towards understanding the emission efficiency of nitride quantum wells,” Phys. Status Solidi A 201(12), 2808–2813 (2004).
[CrossRef]

Lee, J.-L.

J.-L. Lee, M. H. Weber, J. K. Kim, and K. G. Lynn, “Positron annihilation study of Pd contacts on impurity-doped GaN,” Appl. Phys. Lett. 78(26), 4142 (2001).
[CrossRef]

Lee, S.-W.

M.-C. Jeong, B.-Y. Oh, M.-H. Ham, S.-W. Lee, and J.-M. Myoung, “ZnO-nanowire-inserted GaN/ZnO heterojunction light-emitting diodes,” Small 3(4), 568–572 (2007).
[CrossRef] [PubMed]

Li, S.-L.

S.-H. Huang, R.-H. Horng, S.-L. Li, K.-W. Yen, D.-S. Wuu, C.-K. Lin, and H. Liu, “Thermally Stable Mirror Structures for Vertical-Conducting GaN/Mirror/Si Light-Emitting Diodes,” IEEE Photon. Technol. Lett. 19(23), 1913–1915 (2007).
[CrossRef]

Lin, C.-K.

S.-H. Huang, R.-H. Horng, S.-L. Li, K.-W. Yen, D.-S. Wuu, C.-K. Lin, and H. Liu, “Thermally Stable Mirror Structures for Vertical-Conducting GaN/Mirror/Si Light-Emitting Diodes,” IEEE Photon. Technol. Lett. 19(23), 1913–1915 (2007).
[CrossRef]

Lin, Y.-J.

Y.-J. Lin, C.-L. Tsai, Y.-M. Lu, and C.-J. Liu, “Optical and electrical properties of undoped ZnO films,” J. Appl. Phys. 99(9), 093501 (2006).
[CrossRef]

Liu, C.-J.

Y.-J. Lin, C.-L. Tsai, Y.-M. Lu, and C.-J. Liu, “Optical and electrical properties of undoped ZnO films,” J. Appl. Phys. 99(9), 093501 (2006).
[CrossRef]

Liu, H.

S.-H. Huang, R.-H. Horng, S.-L. Li, K.-W. Yen, D.-S. Wuu, C.-K. Lin, and H. Liu, “Thermally Stable Mirror Structures for Vertical-Conducting GaN/Mirror/Si Light-Emitting Diodes,” IEEE Photon. Technol. Lett. 19(23), 1913–1915 (2007).
[CrossRef]

Lu, M.-Y.

X.-M. Zhang, M.-Y. Lu, Y. Zhang, L.-J. Chen, and Z. L. Wang, “Fabrication of a High-Brightness Blue-Light-Emitting Diode Using a ZnO-Nanowire Array Grown on p-GaN Thin Film,” Adv. Mater. 21(27), 2767–2770 (2009).
[CrossRef]

Lu, Y.-M.

Y.-J. Lin, C.-L. Tsai, Y.-M. Lu, and C.-J. Liu, “Optical and electrical properties of undoped ZnO films,” J. Appl. Phys. 99(9), 093501 (2006).
[CrossRef]

Lynn, K. G.

J.-L. Lee, M. H. Weber, J. K. Kim, and K. G. Lynn, “Positron annihilation study of Pd contacts on impurity-doped GaN,” Appl. Phys. Lett. 78(26), 4142 (2001).
[CrossRef]

Megens, M.

J. J. Wierer, A. David, and M. Megens, “III-nitride photonic-crystal light-emitting diodes with high extraction efficiency,” Nat. Photonics 3(3), 163–169 (2009).
[CrossRef]

Myoung, J.-M.

M.-C. Jeong, B.-Y. Oh, M.-H. Ham, S.-W. Lee, and J.-M. Myoung, “ZnO-nanowire-inserted GaN/ZnO heterojunction light-emitting diodes,” Small 3(4), 568–572 (2007).
[CrossRef] [PubMed]

Nakamura, S.

S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
[CrossRef]

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 (2004).
[CrossRef]

Netzel, C.

D. Fuhrmann, C. Netzel, U. Rossow, A. Hangleiter, G. Ade, and P. Hinze, “Optimization scheme for the quantum efficiency of GaInN-based green-light-emitting diodes,” Appl. Phys. Lett. 88(7), 071105 (2006).
[CrossRef]

A. Hangleiter, D. Fuhrmann, M. Grewe, F. Hitzel, G. Klewer, S. Lahmann, C. Netzel, N. Riedel, and U. Rossow, “Towards understanding the emission efficiency of nitride quantum wells,” Phys. Status Solidi A 201(12), 2808–2813 (2004).
[CrossRef]

Noda, S.

S. Noda and M. Fujita, “Light-emitting diodes: Photonic crystal efficiency boost,” Nat. Photonics 3(3), 129–130 (2009).
[CrossRef]

Noguera, C.

J. Goniakowski, F. Finocchi, and C. Noguera, “Polarity of oxide surfaces and nanostructures,” Rep. Prog. Phys. 71(1), 016501 (2008).
[CrossRef]

C. Noguera, “Polar oxide surfaces,” J. Phys. Condens. Matter 12(31), 201 (2000).
[CrossRef]

Oh, B.-Y.

M.-C. Jeong, B.-Y. Oh, M.-H. Ham, S.-W. Lee, and J.-M. Myoung, “ZnO-nanowire-inserted GaN/ZnO heterojunction light-emitting diodes,” Small 3(4), 568–572 (2007).
[CrossRef] [PubMed]

Park, I.-K.

M.-K. Kwon, J.-Y. Kim, I.-K. Park, K. S. Kim, G.-Y. Jung, S.-J. Park, J. W. Kim, and Y. C. Kim, “Enhanced emission efficiency of GaN/InGaN multiple quantum well light-emitting diode with an embedded photonic crystal,” Appl. Phys. Lett. 92(25), 251110 (2008).
[CrossRef]

Park, S.-J.

M.-K. Kwon, J.-Y. Kim, I.-K. Park, K. S. Kim, G.-Y. Jung, S.-J. Park, J. W. Kim, and Y. C. Kim, “Enhanced emission efficiency of GaN/InGaN multiple quantum well light-emitting diode with an embedded photonic crystal,” Appl. Phys. Lett. 92(25), 251110 (2008).
[CrossRef]

Pimputkar, S.

S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
[CrossRef]

Riedel, N.

A. Hangleiter, D. Fuhrmann, M. Grewe, F. Hitzel, G. Klewer, S. Lahmann, C. Netzel, N. Riedel, and U. Rossow, “Towards understanding the emission efficiency of nitride quantum wells,” Phys. Status Solidi A 201(12), 2808–2813 (2004).
[CrossRef]

Rossow, U.

D. Fuhrmann, C. Netzel, U. Rossow, A. Hangleiter, G. Ade, and P. Hinze, “Optimization scheme for the quantum efficiency of GaInN-based green-light-emitting diodes,” Appl. Phys. Lett. 88(7), 071105 (2006).
[CrossRef]

A. Hangleiter, D. Fuhrmann, M. Grewe, F. Hitzel, G. Klewer, S. Lahmann, C. Netzel, N. Riedel, and U. Rossow, “Towards understanding the emission efficiency of nitride quantum wells,” Phys. Status Solidi A 201(12), 2808–2813 (2004).
[CrossRef]

Schubert, E. F.

J. K. Kim, S. Chhajed, M. F. Schubert, E. F. Schubert, A. J. Fischer, M. H. Crawford, J. Cho, H. Kim, and C. Sone, “Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact,” Adv. Mater. 20(4), 801–804 (2008).
[CrossRef]

Schubert, M. F.

J. K. Kim, S. Chhajed, M. F. Schubert, E. F. Schubert, A. J. Fischer, M. H. Crawford, J. Cho, H. Kim, and C. Sone, “Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact,” Adv. Mater. 20(4), 801–804 (2008).
[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 (2004).
[CrossRef]

Sone, C.

J. K. Kim, S. Chhajed, M. F. Schubert, E. F. Schubert, A. J. Fischer, M. H. Crawford, J. Cho, H. Kim, and C. Sone, “Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact,” Adv. Mater. 20(4), 801–804 (2008).
[CrossRef]

Speck, J. S.

S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
[CrossRef]

Tsai, C.-L.

Y.-J. Lin, C.-L. Tsai, Y.-M. Lu, and C.-J. Liu, “Optical and electrical properties of undoped ZnO films,” J. Appl. Phys. 99(9), 093501 (2006).
[CrossRef]

Voigtlander, B.

M. Kästner and B. Voigtlander, “Kinetically Self-Limiting Growth of Ge Islands on Si(001),” Phys. Rev. Lett. 82(13), 2745–2748 (1999).
[CrossRef]

Wang, W.

H. Jia, L. Guo, W. Wang, and H. Chen, “Recent Progress in GaN-Based Light-Emitting Diodes,” Adv. Mater. 21(45), 4641–4646 (2009).
[CrossRef]

Wang, W. K.

W. K. Wang, S. H. Huang, K. S. Wen, D. S. Wuu, and R. H. Horng, “Fabrication and efficiency improvement of micropillar InGaN/Cu light-emitting diodes with vertical electrodes,” Appl. Phys. Lett. 88(18), 181113 (2006).
[CrossRef]

Wang, Z. L.

X.-M. Zhang, M.-Y. Lu, Y. Zhang, L.-J. Chen, and Z. L. Wang, “Fabrication of a High-Brightness Blue-Light-Emitting Diode Using a ZnO-Nanowire Array Grown on p-GaN Thin Film,” Adv. Mater. 21(27), 2767–2770 (2009).
[CrossRef]

Weber, M. H.

J.-L. Lee, M. H. Weber, J. K. Kim, and K. G. Lynn, “Positron annihilation study of Pd contacts on impurity-doped GaN,” Appl. Phys. Lett. 78(26), 4142 (2001).
[CrossRef]

Wen, K. S.

W. K. Wang, S. H. Huang, K. S. Wen, D. S. Wuu, and R. H. Horng, “Fabrication and efficiency improvement of micropillar InGaN/Cu light-emitting diodes with vertical electrodes,” Appl. Phys. Lett. 88(18), 181113 (2006).
[CrossRef]

Wierer, J. J.

J. J. Wierer, A. David, and M. Megens, “III-nitride photonic-crystal light-emitting diodes with high extraction efficiency,” Nat. Photonics 3(3), 163–169 (2009).
[CrossRef]

Wolf, D.

D. Wolf, “Reconstruction of NaCl surfaces from a dipolar solution to the Madelung problem,” Phys. Rev. Lett. 68(22), 3315–3318 (1992).
[CrossRef] [PubMed]

Wu, L. W.

C. H. Kuo, H. C. Feng, C. W. Kuo, C. M. Chen, L. W. Wu, and G. C. Chi, “Nitride-based near-ultraviolet light emitting diodes with meshed p‐GaN,” Appl. Phys. Lett. 90(14), 142115 (2007).
[CrossRef]

Wuu, D. S.

W. K. Wang, S. H. Huang, K. S. Wen, D. S. Wuu, and R. H. Horng, “Fabrication and efficiency improvement of micropillar InGaN/Cu light-emitting diodes with vertical electrodes,” Appl. Phys. Lett. 88(18), 181113 (2006).
[CrossRef]

Wuu, D.-S.

S.-H. Huang, R.-H. Horng, S.-L. Li, K.-W. Yen, D.-S. Wuu, C.-K. Lin, and H. Liu, “Thermally Stable Mirror Structures for Vertical-Conducting GaN/Mirror/Si Light-Emitting Diodes,” IEEE Photon. Technol. Lett. 19(23), 1913–1915 (2007).
[CrossRef]

Yan, P.

X.-S. Fang, C.-H. Ye, L.-D. Zhang, J.-X. Zhang, J.-W. Zhao, and P. Yan, “Direct observation of the growth process of MgO nanoflowers by a simple chemical route,” Small 1(4), 422–428 (2005).
[CrossRef]

Ye, C.-H.

X.-S. Fang, C.-H. Ye, L.-D. Zhang, J.-X. Zhang, J.-W. Zhao, and P. Yan, “Direct observation of the growth process of MgO nanoflowers by a simple chemical route,” Small 1(4), 422–428 (2005).
[CrossRef]

Yen, K.-W.

S.-H. Huang, R.-H. Horng, S.-L. Li, K.-W. Yen, D.-S. Wuu, C.-K. Lin, and H. Liu, “Thermally Stable Mirror Structures for Vertical-Conducting GaN/Mirror/Si Light-Emitting Diodes,” IEEE Photon. Technol. Lett. 19(23), 1913–1915 (2007).
[CrossRef]

Zhang, J.-X.

X.-S. Fang, C.-H. Ye, L.-D. Zhang, J.-X. Zhang, J.-W. Zhao, and P. Yan, “Direct observation of the growth process of MgO nanoflowers by a simple chemical route,” Small 1(4), 422–428 (2005).
[CrossRef]

Zhang, L.-D.

X.-S. Fang, C.-H. Ye, L.-D. Zhang, J.-X. Zhang, J.-W. Zhao, and P. Yan, “Direct observation of the growth process of MgO nanoflowers by a simple chemical route,” Small 1(4), 422–428 (2005).
[CrossRef]

Zhang, X.-M.

X.-M. Zhang, M.-Y. Lu, Y. Zhang, L.-J. Chen, and Z. L. Wang, “Fabrication of a High-Brightness Blue-Light-Emitting Diode Using a ZnO-Nanowire Array Grown on p-GaN Thin Film,” Adv. Mater. 21(27), 2767–2770 (2009).
[CrossRef]

Zhang, Y.

X.-M. Zhang, M.-Y. Lu, Y. Zhang, L.-J. Chen, and Z. L. Wang, “Fabrication of a High-Brightness Blue-Light-Emitting Diode Using a ZnO-Nanowire Array Grown on p-GaN Thin Film,” Adv. Mater. 21(27), 2767–2770 (2009).
[CrossRef]

Zhao, J.-W.

X.-S. Fang, C.-H. Ye, L.-D. Zhang, J.-X. Zhang, J.-W. Zhao, and P. Yan, “Direct observation of the growth process of MgO nanoflowers by a simple chemical route,” Small 1(4), 422–428 (2005).
[CrossRef]

Adv. Mater. (3)

J. K. Kim, S. Chhajed, M. F. Schubert, E. F. Schubert, A. J. Fischer, M. H. Crawford, J. Cho, H. Kim, and C. Sone, “Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact,” Adv. Mater. 20(4), 801–804 (2008).
[CrossRef]

H. Jia, L. Guo, W. Wang, and H. Chen, “Recent Progress in GaN-Based Light-Emitting Diodes,” Adv. Mater. 21(45), 4641–4646 (2009).
[CrossRef]

X.-M. Zhang, M.-Y. Lu, Y. Zhang, L.-J. Chen, and Z. L. Wang, “Fabrication of a High-Brightness Blue-Light-Emitting Diode Using a ZnO-Nanowire Array Grown on p-GaN Thin Film,” Adv. Mater. 21(27), 2767–2770 (2009).
[CrossRef]

Appl. Phys. Lett. (6)

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 (2004).
[CrossRef]

C. H. Kuo, H. C. Feng, C. W. Kuo, C. M. Chen, L. W. Wu, and G. C. Chi, “Nitride-based near-ultraviolet light emitting diodes with meshed p‐GaN,” Appl. Phys. Lett. 90(14), 142115 (2007).
[CrossRef]

J.-L. Lee, M. H. Weber, J. K. Kim, and K. G. Lynn, “Positron annihilation study of Pd contacts on impurity-doped GaN,” Appl. Phys. Lett. 78(26), 4142 (2001).
[CrossRef]

W. K. Wang, S. H. Huang, K. S. Wen, D. S. Wuu, and R. H. Horng, “Fabrication and efficiency improvement of micropillar InGaN/Cu light-emitting diodes with vertical electrodes,” Appl. Phys. Lett. 88(18), 181113 (2006).
[CrossRef]

D. Fuhrmann, C. Netzel, U. Rossow, A. Hangleiter, G. Ade, and P. Hinze, “Optimization scheme for the quantum efficiency of GaInN-based green-light-emitting diodes,” Appl. Phys. Lett. 88(7), 071105 (2006).
[CrossRef]

M.-K. Kwon, J.-Y. Kim, I.-K. Park, K. S. Kim, G.-Y. Jung, S.-J. Park, J. W. Kim, and Y. C. Kim, “Enhanced emission efficiency of GaN/InGaN multiple quantum well light-emitting diode with an embedded photonic crystal,” Appl. Phys. Lett. 92(25), 251110 (2008).
[CrossRef]

IEEE Photon. Technol. Lett. (1)

S.-H. Huang, R.-H. Horng, S.-L. Li, K.-W. Yen, D.-S. Wuu, C.-K. Lin, and H. Liu, “Thermally Stable Mirror Structures for Vertical-Conducting GaN/Mirror/Si Light-Emitting Diodes,” IEEE Photon. Technol. Lett. 19(23), 1913–1915 (2007).
[CrossRef]

J. Appl. Phys. (1)

Y.-J. Lin, C.-L. Tsai, Y.-M. Lu, and C.-J. Liu, “Optical and electrical properties of undoped ZnO films,” J. Appl. Phys. 99(9), 093501 (2006).
[CrossRef]

J. Phys. Condens. Matter (1)

C. Noguera, “Polar oxide surfaces,” J. Phys. Condens. Matter 12(31), 201 (2000).
[CrossRef]

Nat. Photonics (3)

J. J. Wierer, A. David, and M. Megens, “III-nitride photonic-crystal light-emitting diodes with high extraction efficiency,” Nat. Photonics 3(3), 163–169 (2009).
[CrossRef]

S. Noda and M. Fujita, “Light-emitting diodes: Photonic crystal efficiency boost,” Nat. Photonics 3(3), 129–130 (2009).
[CrossRef]

S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
[CrossRef]

Phys. Rev. Lett. (2)

M. Kästner and B. Voigtlander, “Kinetically Self-Limiting Growth of Ge Islands on Si(001),” Phys. Rev. Lett. 82(13), 2745–2748 (1999).
[CrossRef]

D. Wolf, “Reconstruction of NaCl surfaces from a dipolar solution to the Madelung problem,” Phys. Rev. Lett. 68(22), 3315–3318 (1992).
[CrossRef] [PubMed]

Phys. Status Solidi A (1)

A. Hangleiter, D. Fuhrmann, M. Grewe, F. Hitzel, G. Klewer, S. Lahmann, C. Netzel, N. Riedel, and U. Rossow, “Towards understanding the emission efficiency of nitride quantum wells,” Phys. Status Solidi A 201(12), 2808–2813 (2004).
[CrossRef]

Rep. Prog. Phys. (1)

J. Goniakowski, F. Finocchi, and C. Noguera, “Polarity of oxide surfaces and nanostructures,” Rep. Prog. Phys. 71(1), 016501 (2008).
[CrossRef]

Small (2)

M.-C. Jeong, B.-Y. Oh, M.-H. Ham, S.-W. Lee, and J.-M. Myoung, “ZnO-nanowire-inserted GaN/ZnO heterojunction light-emitting diodes,” Small 3(4), 568–572 (2007).
[CrossRef] [PubMed]

X.-S. Fang, C.-H. Ye, L.-D. Zhang, J.-X. Zhang, J.-W. Zhao, and P. Yan, “Direct observation of the growth process of MgO nanoflowers by a simple chemical route,” Small 1(4), 422–428 (2005).
[CrossRef]

Surf. Sci. (1)

V. E. Henrich, “Thermal faceting of (110) and (111) surfaces of MgO,” Surf. Sci. 57(1), 385–392 (1976).
[CrossRef]

Other (1)

E. F. Schubert, in Light Emitting Diodes, 2nd ed.

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Figures (9)

Fig. 1
Fig. 1

Schematic illustrations of light ray incident at various angles from V-LEDs with (a) flat n-GaN and (b) n-GaN/ZnO/MgO nano-pyramids surface.

Fig. 2
Fig. 2

(a) Schematic illustration and (b) SEM image of V-LEDs with ZnO refractive–index modulation layer and MgO nano-pyramids surface

Fig. 3
Fig. 3

SEM images of × 100,000 magnification for the (a) n-GaN/ZnO (600 Å), (b) n-GaN/ZnO/MgO (0.7 μm), (c) n-GaN/ZnO/MgO (2 μm), and (d) n-GaN/ZnO/MgO (4 μm) surfaces.

Fig. 4
Fig. 4

(a) Schematic view of formation process for the tilted MgO pyramid. (b) SEM images of MgO film with 200 nm thickness deposited on non-tilted substrate and 3° tilted substrates.

Fig. 5
Fig. 5

(a) Cross-sectional HR-TEM image of MgO nano-pyramids structure. (b) Schematic crystal structure of MgO pyramid with (200) family plane termination.

Fig. 6
Fig. 6

Light transmittance spectra of ZnO refractive-index modulation layer and MgO layers as a function of film thickness.

Fig. 7
Fig. 7

(a) EL emission spectra measured at 350 mA for V-LEDs with n-GaN, n-GaN/ZnO, and n-GaN/ZnO/MgO surface. (b) The current-voltage (I-V) curves of V-LEDs.

Fig. 8
Fig. 8

Normalized light output power of V-LEDs as a function of surface texturing method. The light output power of V-LEDs with flat n-GaN surface at 350 mA is set as unity. The inset shows a plane-view photomicrograph of an operating V-LEDs.

Fig. 9
Fig. 9

(a) Measured far-field emission intensity from V-LEDs with flat n-GaN and n-GaN/ZnO/MgO (2 μm) nano-pyramids structure surface. (b) The relative enhancement of EL emission intensity as a function of emission angle.

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