Patent ID: 8039291

Claim:
A method of forming a multijunction solar cell comprising an upper subcell, a middle subcell, and a lower subcell comprising: providing a first substrate for the epitaxial growth of semiconductor material; forming an upper first solar subcell on said first substrate having a first band gap; forming a middle second solar subcell over said first solar subcell having a second band gap smaller than said first band gap; forming a graded interlayer over said second solar cell; forming a lower third solar subcell over said graded interlayer having a fourth band gap smaller than said second band gap such that said third subcell is lattice mismatched with respect to said second subcell; attaching a surrogate second substrate over said third solar subcell and removing said first substrate; etching a first trough around the periphery of said solar cell to the surrogate second substrate so as to form a mesa structure on said surrogate second substrate and facilitate the removal of said solar cell from the surrogate second substrate; and etching a second trough around the periphery of said solar cell so as to form a mesa structure on said surrogate second substrate, wherein the second trough lies inside the periphery of the first trough.