Lattice tilt and relaxation in InGaP/GaAs/Ge solar cells on miscut substrates

Strain relaxation and epitaxial layer tilt has been investigated for III-V based tandem solar cells grown on miscut Ge substrates. AlGaAs/InGaP/GaAs l ayers were grown by metalorganic vapour phase epitaxy on substrates miscut by 9 degrees along a low crystallographic symmetry direction. We observe th e GaAs buffer layer grown on the substrate to be 86% relaxed. The GaAs laye r is tilted by 60 arcsec from the substrate, as determined by triple axis x -ray diffraction. This tilt stems from the miscut, the polar/non-polar inte rface and from the miscut direction lying away from a high symmetry directi on. The observed magnitude of the tilt is not predicted well by existing mo dels. Subsequently grown Al0.8Ga0.2As and In0.5Ga0.5P device layers are pse udomorphic with respect to the GaAs buffer layer, and exhibit the expected layer tilting of 58 and 125 arcsec respectively with respect to the Ge subs trate. There is no rotation of the epitaxial layers with respect to the GaA s buffer layer.