The thermal stability of strained SiGe layers that had been grown, via molecular beam epitaxy, onto (100)Si was measured by using Rutherford back-scattering spectrometry, secondary ion mass spectrometry and high-resolution X-ray diffractometry. Diffusion experiments were carried out on 50nm-thick Si1-xGex layers (where x was equal to 0.07, 0.16 or 0.33) that had been annealed at temperatures of between 775 and 1010C for various times. The diffusion of Ge was deduced from broadening of the Rutherford back-scattering spectrometry and secondary ion mass spectrometry Ge profiles, while strain relaxation was deduced from angular shifts of the (400) reflection in high-resolution X-ray diffractometry. The diffusion coefficients which were measured in this way were strongly dependent upon the local Ge concentration in the film. In the tails of the profiles, the diffusion coefficient was comparable with that for Ge in bulk Si. In the center of the film, enhanced diffusion was noted. Both the initial Ge fraction in the as-grown film, and the presence of misfit dislocations, had only a minor effect upon the diffusion behavior. It was concluded that safe thermal processing of such structures was possible for several hours at up to 850C. Germanium Diffusion and Strain Relaxation in Si/Si1-xGex/Si Structures. G.F.A.Van de Walle, L.J.Van Ijzendoorn, A.A.Van Gorkum, R.A.Van den Heuvel, A.M.L.Theunissen, D.J.Gravesteijn: Thin Solid Films, 1989, 183, 183-90