Buffer Layer Effects on Tandem InGaAs TPV Devices

Tandem thermophotovoltaic (TPV) cells have the potential to demonstrate efficiencies exceeding those of single junction devices. Fabricating TPV tandem devices utilizing indium gallium arsenide (InGaAs) for all of the component cells in a two cell tandem necessitates the inclusion of an optically transparent buffer structure in‐between the high bandgap device (In_0.53Ga_0.47As − 0.74eV) and the low bandgap device (In_0.66Ga_0.34As − 0.63eV) to accommodate the ∼1% lattice strain generated due to the change in InGaAs composition. The impact of the buffer structure on the underlying lattice‐matched InGaAs device has been examined by producing 0.74eV InGaAs devices both with and without buffer layers grown on top of them. All structures were characterized by reciprocal space x‐ray diffraction to determine epilayer composition and residual strain. Electrical characterization of the devices was performed to examine the effect of the buffer on the device performance. The electrical impact of the buffer structure depends upon where it is positioned. When near the emitter region, a 260% increase in dark current was measured, whereas no change in dark current was observed when it was near the base region.