Fluorescence microscopy investigation of InGaN-based light-emitting diodes

The authors image the spatial dependent luminescent properties of InGaN quantum wells (QWs) in light-emitting diodes (LEDs) using fluorescence microscopy with selective excitation of the QWs through the transparent sapphire substrate. The authors measure strong carrier escape with the associated photovoltaic effect in the device under open and short circuit conditions. The addition of electrical contacts allows comparison of the images under both optical and electrical excitation. A lateral distribution of the junction potential is measured in LEDs with structured metal contacts. An ohmic contact creates an equipotential surface and influences the collective emission. The technique offers useful insights into the spatial properties of the recombination processes in InGaN materials and LED fabrication processes at low forward bias.