Si/multicrystalline-SiGe heterostructure as a candidate for solar cells with high conversion efficiency

We report on growth and characterizations of Si/multicrystalline-SiGe (mc-SiGe) heterostructure as a promising candidate to surpass multicrystalline-Si solar cells. A 0.5 μm-thick Si thin film was grown on mc-SiGe using a solid-source molecular beam epitaxy system. Spatial distribution of the status of strain in Si was found to be strongly dependent on the composition and microstructure of underlying mc-SiGe. Large strain distribution and partial strain relaxation were revealed in Si on mc-SiGe with average Ge composition of 0.72. On the other hand, almost uniformly strained-Si film was grown on mc-SiGe with average Ge composition of 0.30. To avoid introduction of recombination centers at the Si/SiGe interface, it is necessary to avoid strain relaxation by decreasing average Ge composition in mc-SiGe.