Strain relaxation of Ge_1-xSi_x buffer systems grown on Ge (001)

We have investigated the strain relaxation behavior of biaxial tensile strained Ge_1-xSi_x buffer systems grown on Ge (001) by a high-resolution x-ray reciprocal space mapping technique. The molecular beam epitaxy grown structures contain a linearly graded buffer, followed by a uniform buffer and a modulation-doped heterostructure with a high mobility two-dimensional hole gas in a Ge channel. Our quantitative measurements of the in-plane strain show that the lower part of the graded buffer is completely strain relaxed, while the top part of this region and the uniform alloy buffer are partly strain relaxed showing a linear increase of strain towards to surface.