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 N-2 ambient at 600, 700 and 750 degreesC. 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, y(Ge) = 0.27-0.35 and 0.10-0.17, were found to be not fully relaxed even after annealing at 750 degreesC. 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 SiO2Ge0.8 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. (C) 2002 Elsevier Science B.V. All rights reserved.