High external quantum efficiency from double heterostructure InGaP/GaAs layers as selective emitters for thermophotonic systems
In thermophotovoltaics (TPV) an emitter is heated up to a high temperature and emits infrared light. Above bandgap photons can then be converted into power by photovoltaic cells at room temperature. One of the main disadvantages of TPV is the need for a highly perfect selective emitter or filter to achieve high conversion efficiency. Thermophotonics overcomes this through the use of a heated light-emitting diode as an extremely selective emitter. To achieve net conversion of heat to electricity with thermophotonics, a LED with high electroluminescence efficiency is required. As the initial step to demonstrate this concept, a GaInP/GaAs double heterostructure was optically pumped with energy higher than bandgap at room temperature. An external quantum efficiency (EQE) of 96% was measured for an undoped planar sample on a transparent substrate using light extraction schemes. This EQE is close to achieving the cooling from the lattice. The results agree well with independent thermal measurements on planar samples. The low surface recombination velocity implies that the sample quality is excellent. However, not all samples with that feature will meet device-quality level. The excellent device performance also relies on processing techniques and design.