Structural properties of directionally grown polycrystalline SiGe for solar cells

We investigated structural properties of polycrystalline SiGe grown by directional growth method for solar cells. The average Ge composition was systematically changed in the range between 0 and 10 at%. Distributions of concentration and crystallographic orientation in the SiGe crystal were measured and the preferential growth orientation was found to change from (1 1 1) to (1 1 0) with increasing average Ge composition. Misfit dislocation was observed using transmission electron microscope. There was few dislocations in SiGe crystals when the average Ge composition was between 0 and 5 at% though a lot of dislocations existed at the average Ge composition of 10 at%. We concluded that the optimum Ge composition is around 5 at% for solar cells.