Patent ID: 9691928
Date: 2017-06-27
CPC Classifications: H01L,Y02E,Y02P

Claim:
1. A method of forming a multijunction solar cell comprising at least an upper subcell, a middle subcell, and a lower subcell, the method comprising: providing a first substrate for an epitaxial growth of semiconductor material; forming a first solar subcell on said substrate having a first band gap; forming a second solar subcell over said first solar subcell having a second band gap smaller than said first band gap; forming a first alpha layer composed of GaInP over said second solar subcell using a surfactant including selenium, wherein the selenium is introduced as a precursor gas of di-isopropyl selenide, and the first alpha layer is configured to prevent threading dislocations from propagating; forming a metamorphic grading interlayer over and directly adjacent to said first alpha layer, said grading interlayer having a third band gap greater than said second band gap, and the grading interlayer having a different composition than the first alpha layer; forming a second alpha layer composed of GaInP using a surfactant including selenium over and directly adjacent to said grading interlayer to prevent threading dislocations from propagating, wherein the selenium is introduced as a precursor gas of di-isopropyl selenide, and the second alpha layer has a different composition than the grading interlayer; and forming a third solar subcell over said grading interlayer having a fourth band gap smaller than said second band gap such that said third solar subcell is lattice mismatched with respect to said second solar subcell; the grading interlayer being compositionally graded with a lattice constant that matches the lattice constant of the second solar subcell on a first side and matches the lattice constant of the third solar subcell on a second side; and the grading interlayer having a different composition than each of the first and second alpha layers; wherein each alpha layer is between 0.2 and 0.5 microns in thickness and doped with the selenium from 1.0×10