X-ray standing wave study of Si/Ge/Si(0 0 1) heterostructures grown with Bi as a surfactant

X-ray standing wave (XSW) analysis was used for an atomic-scale structural study of ultra-thin Si/Ge heterostructures grown on Si(0 0 1) by surfactant mediated epitaxy with Bi as the surfactant. XSW measurements were performed for the Si(0 0 4) and Si(0 2 2) Bragg reflections for Ge coverages from 1 to 10 monolayers. The measured Ge coherent positions agree with the calculated Ge positions for a tetragonally distorted Ge lattice formed on Si(0 0 1) using continuum elasticity theory. However, the measured Ge coherent fractions are smaller than expected. The quality of the Si cap layer and its registry with the underlying Si(0 0 1) substrate lattice was also determined by combining the XSW technique with evanescent-wave emission.