0.6-eV bandgap In/sub 0.69/Ga/sub 0.31/As thermophotovoltaic devices grown on InAs/sub y/P/sub 1-y/ step-graded buffers by molecular beam epitaxy

Single-junction, lattice-mismatched (LMM) In/sub 0.69/Ga/sub 0.31/As thermophotovoltaic (TPV) devices with bandgaps of 0.60 eV were grown on InP substrates by solid-source molecular beam epitaxy (MBE). Step-graded InAs/sub y/P/sub 1-y/ buffer layers with a total thickness of 1.6 μm were used to mitigate the effects of 1.1% lattice mismatch between the device layer and the InP substrate. High-performance single-junction devices were achieved, with an open-circuit voltage of 0.357 V and a fill factor of 68.1% measured at a short-circuit current density of 1.18 A/cm² under high-intensity, low emissivity white light illumination. Device performance uniformity was outstanding, measuring to better than 1.0% across a 2-in diameter InP wafer indicating the promise of MBE growth for large area TPV device arrays.