Strain-compensated InGaAs/InGaAs quantum well cell with 2 micron band-edge

Strain-compensated Quantum Well Cells (QWCs) have been shown to extend the absorption to longer wavelengths than attainable with lattice-matched material, while retaining a similar or better dark current. This is of particular interest for thermophotovoltaic (TPV) applications with low temperature sources where low energy bandgaps are required, for example in combination with a Holmia emitter of 1.95 mum peak emission. Here we report on a two quantum well In0.74Ga0.26As/In0.36Ga0.64As device which absorbs out to 2040 rim, as observed by cathodoluminescence. Our modelling of the spectral response, including quantum and strain effects, is also consistent with this result. We show that the material quality measured by transmission electron microscopy (TEM) is excellent, exhibiting sharp interfaces. However, the electrical properties under illumination are less encouraging: At room temperature not all carriers are collected in forward bias. We present results on the field and temperature dependence of carrier escape and collection.