Planar substrate-emitting-microcavity light-emitting diodes with 20% external QE

The external QE of microcavity light emitting diodes strongly depends on the device size and operational current density. Our experiments reveal that spectral broadening of the optical spectrum emitted by the three InGaAs QW's as well as photon recycling of photons originally emitted into the guided mode of the cavity can explain these differences. An optimized microcavity layer design yielded external QE's of 20% for substrate emitting light emitting diodes with diameters of 1.5 mm.