Light extraction limits in textured GaN-InGaN light-emitting diodes: Radiative transfer analysis

We present a study on the light extraction properties of thin film light-emitting diodes (LEDs) based on the radiative transfer theory. We show that the well known ergodic limit for absorptivity in textured solar cells also applies to emissivity in LEDs accordance with the Kirchhoff's radiation law. This limit for the emission enhancement by surface texturing in LEDs is fundamental and cannot be exceeded even with index-matched optics. We further carry out numerical calculations accounting for realistic absorption in typical GaN-InGaN LEDs to compare their performance with the ergodic limit for non-absorbing structures. The results show that the optical power of InGaN-GaN LED designs can be improved by a substantial factor of 2-4 with textured surfaces and engineering of the emission pattern and provide a guideline for more efficient LED designs. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3655155]