Boron diffusion in in situ doped Si1−xGex and Si, subjected to inert‐ambient furnace annealing at 800 °C, was investigated. For Si1−xGex, the effect of biaxial compressive and tensile strain on boron diffusion was studied using Si1−xGex layers with a constant Ge content (x≊0.10 and x≊0.20) grown epitaxially on various relaxed Si1−yGey (0≤y≤0.20) substrates. Boron diffusion is primarily a function of Ge content, x in the Si1−xGex layers, and does not show a strong dependence on macroscopic biaxial strain. For Si, the effect of biaxial tension was investigated using relaxed Si1−yGey layers as substrate templates for epitaxial Si layers. As in Si1−xGex, boron diffusion in Si does not depend strongly on biaxial strain. © 1995 American Institute of Physics.