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Keywords:

  • GaN;
  • LEDs;
  • patterned sapphire substrate;
  • light extraction efficiency

Abstract

The GaN-based LEDs external quantum efficiency (EQE) is significantly improved by using the patterned sapphire substrate (PSS) technique. The enhancements in the light extraction efficiency (LEE) and the internal quantum efficiency (IQE) were evaluated based on a rate equation analysis of EQE versus the square root of the light-output power (EQE-√P) curves. The estimated enhancement in the LEE was much larger than that in the IQE. The detailed mechanism of improving the LEE by PSS technique was investigated using Monte-Carlo ray tracing simulation. The LEE increased with the pattern height, and tended to be saturated when the height was over 1.5 μm. These results indicate that the improved light output power of GaN-based LEDs on PSS is mainly due to the enhancement in LEE. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)