Results are presented on planar microcavity light emitting diodes with different device diameters. A record external quantum efficiency of 20&percent; is achieved for a 1.5 mm light emitting diode. The strong dependence of the quantum efficiency on current density and device size are compared with theoretical results. A good correspondence is obtained when spectral broadening and photon recycling are taken into account. ©1997 American Institute of Physics.