Dynamical X-Ray Diffraction Analysis of Triple-Junction Solar Cells on Germanium (001) Substrates

We demonstrate the dynamical x-ray diffraction analysis of metamorphic triple-junction solar cells grown on Ge (001) substrates. The solar cells investigated involve an In_0.67Ga_0.33P top cell, an In_0.17Ga_0.83As middle cell, and a Ge bottom cell. A graded buffer layer is inserted between the bottom and middle cells for the purpose of accommodating the lattice mismatch. Linearly-graded, step-graded, and S-graded compositional profiles were considered for this buffer layer. The x-ray rocking curve analysis for a number of hkl reflections including 004, 113, 116, 044, 026, and 117 was conducted for the case of Cu Kα₁ radiation. We show that the use of non-destructive x-ray analysis allows determination of the threading dislocation densities in the top two cells. In the cases of S-graded or step-graded buffer layers, the buffer threading dislocation density could also be estimated.