Ingaas/ingaas strain-compensated quantum well cells for thermophotovoltaic applications

Strain-compensated layers in photovoltaic devices can yield unique advantages as the absorption threshold can be extended towards longer wavelengths beyond that of the lattice-matched material, which is particularly important for thermophotovoltaic (TPV) applications. In such a nanostructure, where InGaAs barriers and InGaAs quantum wells of appropriate compositions are strain compensated on an InP substrate, the absorption of a quantum well cell (QWC) can be extended to about 2 microns. Due to the higher band-gap barriers, the dark current remains at a low level more appropriate to lattice-matched InGaAs. Great care has to be taken in design and growth to achieve a situation that is close to strain balance with zero stress. Results are presented on a strain-compensated QWC that absorbs out to 1.77 microns. Predictions show that strain-compensated InGaAs/InGaAs QWCs have superior performance when compared with bulk InGaAs on InP monolithic interconnected modules and GaSb TPV cells.