Structure determination of the clean (001) surface of strained Si on Si_1−xGe_x

The surface structure of the strained Si(001) (thickness of 20 nm) on Si_1−xGe_x (x = 0.1, 0.2, and 0.3) was studied by low-energy electron diffraction (LEED). LEED intensity-energy spectra of the 2 × 1 reconstructed clean surfaces showed a systematic change that indicates the lattice contraction along the [001] direction remains even at the surfaces. The atomic structures were quantitatively determined, and they were compared with the unstrained pristine Si. The differences in the atomic position almost follow the difference in the bulk lattice constant determined by X-ray diffraction measurements. The results indicate that the strain produced at the Si/Si_1−xGe_x interface remains unchanged up to the surface layer