Wiesmann, ChristopherBergenek, KristerHoudre, RomualdStanley, Ross P.Linder, NorbertSchwarz, Ulrich T.2010-11-302010-11-302010-11-30200910.1109/JQE.2009.2024551https://infoscience.epfl.ch/handle/20.500.14299/59842WOS:000270147300001A theoretical approach based on coupled-mode theory is presented in order to determine the radiation pattern of LEDs incorporating a shallow photonic crystal. From this, a fundamental limit for the directionality of the diffraction of a single guided mode is given. Additionally, the Fabry-Perot resonances are shown to have significant impact on the directionality of diffracted light. For a realistic green-emitting InGaN LED in thin-film configuration the optimum reciprocal lattice vector is derived in terms of absolute diffracted intensity and directionality within a limited acceptance angle. The latter can be as high as 1.8 times the directionality of a Lambertian emitter. Furthermore, the spontaneous emission distribution between guided modes heavily influences the diffracted intensity.Coupled-mode theorydiffractionLEDsphotonic crystals (PhCs)Light-Emitting-DiodesHigh Extraction EfficiencySpontaneous Emissiontext::journal::journal article::research article