Accurate measurement of external quantum efficiency of semiconductors for thermophotonics

To achieve net conversion of heat to electricity with thermophotonics, a LED with high external quantum efficiency (EQE) is required. As part of the initial stages of making a thermophotonic device, we have developed a system for accurately measuring the external quantum efficiency of highly radiatively efficient structures. The technique involves measuring uncalibrated photoluminescence and thermal signals from an optically pumped structure, as a function of incident laser power. This allows an increase in fractional luminescence to be calibrated against a decrease in fractional heating. In initial results we have measured an external quantum efficiency of 86% from a GaAs/AlGaAs double heterostructure, with a lower than optimum power density. This is one of the highest EQE values ever reported.