Application of high-resolution X-ray diffraction to study strain status in Si1−xGex/Si1−yGey/Si (001) heterostructures

High resolution X-ray diffraction was used to study the thermal stability and strain relaxation mechanisms in p-type modulation doped Si1−xGex/Si1−yGey/Si(001) heterostructures on virtual substrates. Ex-situ post-growth furnace thermal treatments were done in a N2 ambient at 600, 700 and 750 °C. It was found that the high temperature annealing leads to the full relaxation of the intermediate part of the virtual substrate (corresponding to the Ge composition range of y=0.17–0.27). Both the uppermost and lowermost parts of the virtual substrate regions with, respectively, yGe=0.27–0.35 and 0.10–0.17, were found to be not fully relaxed even after annealing at 750 °C. The use of the Hotbird X-ray diffractometer with its powerful rotating anode source allowed us to reveal and study the very weak intensity scattering from a 4nm thick Si0.2Ge0.8 channel. The increase of the annealing temperature leads to a broadening of the channel layer with a decreasing of its Ge concentration though remaining fully strained.