Strain relaxation and epitaxial layer tilt has been investigated for III-V based tandem solar cells grown on miscut Ge substrates. AlGaAs/InGaP/GaAs layers were grown by metalorganic vapour phase epitaxy on substrates miscut by 9° along a low crystallographic symmetry direction. We observe the GaAs buffer layer grown on the substrate to be 86% relaxed. The GaAs layer 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 interface and from the miscut direction lying away from a high symmetry direction. The observed magnitude of the tilt is not predicted well by existing models. Subsequently grown Al0.8Ga0.2As and In0.5Ga0.5P device layers are pseudomorphic with respect to the GaAs buffer layer, and exhibit the expected layer tilting of 58 and 125 arcsec respectively with respect to the Ge substrate. There is no rotation of the epitaxial layers with respect to the GaAs buffer layer.

We applied high resolution x-ray diffraction techniques to determine the three dimensional domain shape in nominally lattice-matched, CuPt B ordered, In x Ga 1-x P epitaxial layers deposited on GaAs by metal organic vapor phase epitaxy. A technique of reciprocal space mapping is described which provides threedimensional information on the shape and size of the ordered domains. The domain shape is obtained by reciprocal space mapping along orthogonal crystallographic directions. Applying this technique shows that, at large miscut angles, the domains are oriented close to the growth direction, and are elongated by differing extents along the [110] and [ -110].

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