Study of the internal quantum efficiency of AlGaInP Microcavity Light-Emitting Diodes

Detailled study of external quantum efficiency eta (QE) is reported for AlGaInP-based Microcavity Light-Emitting Diodes (MCLEDs). Unlike conventional LED's the extraction efficiency gamma (ext) and far field profile depend on the linewidth of the intrinsic spontaneous emission and wavelength detuning between cavity mode and peak electroluminescence. This dependence makes it difficult to estimate the intrinsic spectrum, hence the performances of MCLED's. By using a nondestructive deconvolution technique, the intrinsic spectra of a MCLED and a reference LED (with the same active regions) could be determined at different current densities. This allowed precise calculation of gamma (ext) for both devices (values close to 11% were found for the MCLED), hence of their apparent internal quantum efficiencies eta (int). At 55 A/cm2, values of 90% and 40% were determined for the LED and MCLED respectively. In order to explain this difference, we measured eta (QE) for devices with different sizes. From a fitting procedure based on a simple model taking into account the device size, we found out that the radiative efficiencies of LEDs and MCLEDs were close to 90%. We concluded that the low eta (int) of MCLED was due to a bad current injection, and especially to electron leakage current, as confirmed by numerical simulations.