Hybrid III-V/SiGe solar cells on Si substrates and porous Si substrates
Pablo Caño1, Huy Nguyen2, Aled Morgan2, Manuel Hinojosa1, Iván Lombardero1, Iván García1, Luis Cifuentes1, David Fuertes1, Andrew Johnson2, Ignacio Rey-Stolle1
1Instituto de Energía Solar - Universidad Politécnica de Madrid, Madrid, Spain
/2IQE plc, Cardiff, United Kingdom

The combination of the high performance of III–V semiconductors with the low cost of silicon substrates is the target of numerous research lines. In this context, we have developed a hybrid GaAsP/SiGe grown on silicon substrates employing group IV reverse graded buffer layers, but, in contrast to previous designs, incorporating a porous silicon layer in the substrate subsurface.
After growth in both CVD and MBE reactors, the epi-wafers were characterized by ECV, SEM, SIMS, AFM, XRD and PR. Then, the solar cells were manufactured with photolithography and measured by means of I-V curves, ER and QE.
Although reverse graded buffer layers can reduce the threading dislocation density and allow the growth of thinner buffers, they have shown to be prone to the appearance of cracks, as observed. But, the incorporation of the porous silicon buffer has repressed crack propagation thanks to its ductility. This crack reduction turns into a minimization of the problems of low shunt resistance observed before and thus, improving solar cell performance.
Further characterization on this samples is ongoing and a new cohort of devices is being manufactured, whose results would be available for the final paper.    

Area: Sub-Area 3.3: Hybrid Tandem/Multijunction Solar Cells