Design and characterization of top-emitting microcavity light-emitting diodes

High-efficiency top-emitting InGaAs/AlGaAs microcavity light-emitting diode s (MCLEDs) have been optimized and fabricated. The structures were grown us ing molecular beam epitaxy on GaAs substrates. They consist of a three-peri od Be-doped distributed Bragg reflector (DBR) centred at 950 nm wavelength, a cavity containing three InGaAs quantum wells and a 15-period Si-doped DB R. Different values for the wavelength detuning between the spontaneous emi ssion line and Fabry-Perot cavity mode were explored, between -40 nm and +1 0 nm. Devices sizes ranged from 22 x 22 mu m(2) to 420 x 420 mu m(2). As ex pected from simulations, the higher efficiencies are obtained when the detu ning is in the -20 to 0 nm range. The devices exhibit up to 10% external qu antum efficiency, measured for a 62 degrees collection half-angle. After co rrection for the surface shadowing due to the grid p-contact, the maximum e fficiency increases to 14% and is practically independent of device size. 0 .5% external quantum efficiency (1.5% when corrected for shadowing) was ach ieved for light butt coupled directly into a 100 mu m diameter silica fibre .