  A tandem GaAsP/SiGe solar cell has been developed employing group-IV reverse
buffer layers grown on silicon substrates with a subsurface porous layer.
Reverse buffer layers facilitate a reduction in the threading dislocation
density with limited thicknesses, but ease the appearance of cracks, as
observed in previous designs grown on regular Si substrates. In this new
design, a porous silicon layer has been incorporated close to the substrate
surface. The ductility of this layer helps repress the propagation of cracks,
diminishing the problems of low shunt resistance and thus improving solar cell
performance. The first results of this new architecture are presented here.
