Direct measurement of surface stress during Bi-mediated Ge growth on Si

We have focused on stress measurements during Bi termination of Si (111) and Ge growth on this Bi-mediated Si (111). In order to obtain information on both the surface stress and the surface structure simultaneously, we have combined the surface-curvature and the reflection-high-electron-energy-diffraction instrumentations in an identical ultrahigh vacuum system. We find the Bi-terminated Si (111) √3 × √3-β surface releases 1.8 N/m (= J/m2), or (1.4 eV/(1 × 1 unit cell)), of the surface energy from the strong tensile Si (111) 7 × 7 reconstruction. Subsequent Ge deposition on the Bi-terminated Si surface develops a compressive stress, which oscillates with a period corresponding to the growth of a single bilayer. The real-time stress measurement provides a direct evidence for this oscillatory stress relaxation in the layer-by-layer growth.