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Enhance O utput Power of GaN -Based LEDs With Nano-Pattern Sapphire Substrate

IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 20, NO. 13, JULY 1, 2008. Enhance O utput Power of GaN -Based LEDs With Nano-Pattern Sapphire Substrate. J. J. Chen, Y. K. Su , Fellow, IEEE , C. L. Lin, S. M. Chen, W. L. Li, and C. C. Kao. Introduction.

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Enhance O utput Power of GaN -Based LEDs With Nano-Pattern Sapphire Substrate

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  1. IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 20, NO. 13, JULY 1, 2008 Enhance Output Power of GaN-Based LEDs With Nano-Pattern Sapphire Substrate J. J. Chen, Y. K. Su, Fellow, IEEE, C. L. Lin, S. M. Chen, W. L. Li, and C. C. Kao

  2. Introduction • Large lattice mismatch and thermal expansion between the epitaxial GaN film and sapphire substrate, high threading dislocation densities degrade the internal quantum efficiency of the LED. • Light extraction efficiency is also an important factor to enhance the output power of the LED. • With PSS and ELO we can significantly eliminate the threading dislocations. With reduced geometrical size of sapphire patterns can increase the number of patterns, and then increase the opportunity of light scattering.

  3. Experiment STEP • Polystyrene spheres with diameter 500nm spun on sapphire substrate. • ICP by Cl2-BCl3 Pattern information • Diameter:450nm • Spacing:50nm • Depth:150nm

  4. Experiment • Compare with conventional sapphire substrate and PSS(diameter:3μm spacing:3μm depth:1.5 μm).

  5. Result and discussion Leakage currents at -5V NPSS:18nA CSS:192nA

  6. Result and discussion External quantum efficiencies NPSS:16.39% PSS :14.97% CSS :12.59% 10.27mW 9.27mW Output power NPSS:10.27mW→1.3 times of CSS →1.1 times of PSS PSS : 9.27mW CSS : 7.93mW 7.93mW • Some voids were formed at the GaN/NPSS interface leads to the output power will saturated at high injection current(ex:100mA) because the void blocked the thermal flow path.

  7. Conclusion • The measurement result of HRXRD, EPD, and leakage currents infer the crystalline quality of the epitaxial LED film improved by the NPSS technique. • The output power increased by improving the light extraction efficiency via nano-patterns and the density of threading dislocation by using NPSS technique. • Void problem will cause thermal dissipation at high injection current.

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