In situ X-ray investigation of the high-temperature behaviour of strained Si1-xGex/Si and Si1-yCy/Si heterostructures

Pseudomorphic Si1-xGex (0.15<x<0.35) and Si1-yCy (0.008<y<0.016) thin epilayers on Si(100) substrate, grown by rapid thermal chemical vapour deposition and molecular beam epitaxy, were investigated at annealing temperatures up to 1000 degrees C. To measure in situ the variation of the epilayer lattice constant, a conventional X-ray powder diffractometer with high-temperature attachment in combination with a high-power X-ray generator was used. From the decrease in the angular distance between substrate and epilayer reflection, the strain state of the system can be obtained. In the compressive strained Si1-xGex/Si system, strain relaxation could be observed, which is explicable in terms of the introduction of misfit dislocations at the interface. At temperatures of about 1000 degrees C an additional effect, the interdiffusion of Si and Ge and thus the decrease in the Ge concentration inside the layer, enhances the relief of the strain. Both effects were separately measurable and the diffusion coefficient was determined in its dependence on the Ge content. On the other hand, in the tensile strained Si1-yCy/Si system the nucleation and diffusion-controlled growth of SiC nanocrystals was found to be the dominant mechanism at temperatures above 800 degrees C, decreasing the amount of C atoms on substitutional sites and thus relieving the strain in the layer.