NOVELTY - The process comprises depositing a separation layer on a first substrate, depositing a sequence of layers of semiconductor material on the separation layer to form a solar cell, mounting and bonding a surrogate substrate (125) on top of the sequence of layers, attaching a connecting link element to two opposed points on the periphery of the surrogate substrate, and etching the separation layer while applying tension to the link element to remove the epitaxial layer from the first substrate. The separation layer has a thickness of 1000 Angstrom .    USE - The process is useful for selectively freeing an epitaxial layer from a single crystal substrate, where the epitaxial layer is useful for making multijunction solar cell for space applications and terrestrial solar power applications.    ADVANTAGE - The process is capable of rapidly and economically manufacturing the solar cell with improved power and energy conversion efficiency by efficiently freeing the epitaxial layer from the single crystal substrate, reduces the recombination loss at the backside of the solar subcell, and minimizes threading dislocations from propagating in the active regions.    DETAILED DESCRIPTION - The process comprises depositing a separation layer on a first substrate, depositing a sequence of layers of semiconductor material on the separation layer to form a solar cell, mounting and bonding a surrogate substrate (125) on top of the sequence of layers, attaching a connecting link element to two opposed points on the periphery of the surrogate substrate, and etching the separation layer while applying tension to the link element to remove the epitaxial layer from the first substrate. The separation layer has a thickness of 1000 Angstrom . The surrogate substrate is composed of a polyimide material. The tension applied to the link element allows the epitaxial layer and the surrogate substrate to curl upward permitting the out diffusion of reaction products of the etching process. The deposition of the sequence of layers comprises forming an upper first solar subcell on the first substrate having a first band gap, forming a middle second solar subcell over the first solar subcell having a second band gap smaller than the first band gap, forming a graded interlayer over the second solar cell, and forming a lower third solar subcell over the graded interlayer having a fourth band gap smaller than the second band gap such that the third subcell is lattice mismatched with respect to the second subcell. The deposition of the sequence of layers comprises forming an upper first subcell on the first substrate comprising a first semiconductor material with a first band gap and a first lattice constant, forming a middle second subcell over the first solar subcell comprising a second semiconductor material with a second band gap and a second lattice constant, forming a lattice constant transition material positioned between the first subcell and the second subcell, forming a graded interlayer over the second solar cell, and forming a lower third solar subcell over the graded interlayer having a fourth band gap smaller than the second band gap such that the third subcell is lattice mismatched with respect to the second subcell. The second band gap is less than the first band gap. The second lattice constant is greater than the first lattice constant to the second lattice constant. The lattice constant transition material has a lattice constant that changes gradually from the first lattice constant to the second lattice constant. The transition material and graded interlayer have in-plane lattice parameter greater or equal to that of the first subcell and less than or equal to that of the second subcell, and a band gap energy greater than that of the second subcell, and the band gap of the transition material remains constant at 1.50 eV throughout its thickness.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross-sectional view of a solar cell.    Contact layer (104)    Bonding layer (124)    Surrogate substrate (125)    Dielectric coating layer (130)    Channel. (511)