Interdiffusion measurements in asymmetrically strained SiGe/Si superlattices

Interdiffusion measurements are reported for Si_0.65Ge _0.35/Si asymmetrically strained superlattices grown by molecular beam epitaxy at 530°C. The temperature-dependent interdiffusion coefficient obtained from x-ray diffraction can be described by D=675 exp(-4.4 eV/kT)cm ²/s in the temperature range 700-880°C. Initially, an enhanced diffusion was observed, especially near the superlattice surface. This is attributed to the presence of nonequilibrium defects. Bulk interdiffusion measurements were made only after isoconfigurational conditions were attained. The diffusion analysis first formulated by J. W. Cahn [Acta Metall. 9, 795 (1961)] is applied here, and the relative importance of both gradient energy effects and coherency strain effects will be discussed.