Design and characterization of top-emitting microcavity light-emitting diodes
High-efficiency top-emitting InGaAs/AlGaAs microcavity light-emitting diodes (MCLEDs) have been optimized and fabricated. The structures were grown using molecular beam epitaxy on GaAs substrates. They consist of a three-period Be-doped distributed Bragg reflector (DBR) centred at 950 nm wavelength, a cavity containing three InGaAs quantum wells and a 15-period Si-doped DBR. Different values for the wavelength detuning between the spontaneous emission line and Fabry-Perot cavity mode were explored, between -40 nm and +10 nm. Devices sizes ranged from 22 x 22 mu m(2) to 420 x 420 mu m(2). As expected from simulations, the higher efficiencies are obtained when the detuning is in the -20 to 0 nm range. The devices exhibit up to 10% external quantum efficiency, measured for a 62 degrees collection half-angle. After correction for the surface shadowing due to the grid p-contact, the maximum efficiency increases to 14% and is practically independent of device size. 0.5% external quantum efficiency (1.5% when corrected for shadowing) was achieved for light butt coupled directly into a 100 mu m diameter silica fibre.