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2 Fundamental problems of LEDs

  • Limited conversion of electrical to optical energy
  • A Large proportion of Emitted light trapped inside high index GaN layer.

Photonic crystals

  • Provide optimal leakage mechanism for light trapped in high index layers.
  • Improves extraction efficiency.
  • Increase efficiency of light emission
  • Potentially, they can increase the total efficiency to more than 75%

A typical LED structure currently possesses over 40 trapped waveguide modes confined in the high index GaN material. The Photonic Crystal provides an optimised mechanism for allowing these trapped modes to be extracted. This ultimately increases the light extraction of an LED and subsequently improves the overall efficiency of the LED. This can potentially provide LED devices with overall wall plug efficiencies of over 75%.

If the top right hand figure is examined we can see that in a conventional LED structure only 4.35% of the light is extracted from the top and 4.35% from the bottom surface of the LED. The remaining light is trapped in the core (67.8%) and in the sapphire substrate (23.5%). This can be attributed to the allowed escape cone angle at the GaN/air interface being 24.1 degrees. Please see bottom right figure. In this conventional case only light residing inside this escape cone is actually extracted from the LED structure while light emitting outside this cone angle is trapped in the semiconductor material.

Mesophotonics offers a proprietary engineered high order symmetry photonic crystal design that delivers significant improvement in the LED efficiency as well as useable light coupled into the application.