Thin semiconducting layers as selective emitters in thermophotonic systems

The main difficulty in achieving high efficiency with thermophotovoltaics (TPV) is that nearly perfect recycling or suppression of below bandgap radiation is required. Selective emitters and filters have been developed to address this issue but the degree of perfection required means that recycling of infrared radiation remains a challenge. Here, we investigate a new way to approach high efficiency with a concept called ´thermophotonics´. The advantage of this concept is that no filter is required due to the extremely selective emitter formed by a highly efficient, forward-biased light-emitting diode (LED). To achieve net conversion of heat to electricity with thermophotonics, a LED with high external quantum efficiency (EQE) is required. As the initial step to demonstrate this concept, a double heterostructure (DH) was optically pumped with energy higher than bandgap at room temperature and an EQE of 60% was achieved without any light-extraction scheme. Applying a light extraction scheme is expected to significantly improve this value. In this paper, the fabrication of high EQE devices and measurement of their optical properties is discussed together with the preliminary EQE results.