Strain relaxation in metamorphic InAlAs buffers

The strain relaxation in a metamorphic InxAl1−xAs buffer placed on top of an AlAs/GaAs superlattice (SL) was analyzed using high-resolution X-ray diffraction and compared to a reference sample containing no SL. Pole figures were constructed to characterize the strain relaxation and twist in the metamorphic buffer layers, AlAs/GaAs SL and GaAs substrate. Lattice mismatch induced strain within such heterostructure causes tilt angles of the layers inside the buffer to rotate around the surface normal. The strong disorder observed in the AlAs/GaAs superlattice supports our previous finding that an AlAs/GaAs SL in the virtual substrate is important for strain relaxation on the substrate side.