X-ray standing waves (XSW) and grazing incidence x-ray diffraction (GIXD) were used to investigate the crystallinity of ultrathin Ge films grown by molecular-beam epitaxy on Si(001) with and without Te as a surfactant. The Ge layer thickness ranged from 1 to 10 ML. The results clearly indicate that Ge films grown with Te have a higher degree of crystallinity compared to those grown without Te. For example, GIXD shows that 9 ML Ge grown on Si(001) with Te is strained in plane; while the same film grown without Te is relaxed. The (004), (022), and (008) XSW results are used to determine the registry of the Ge atoms with respect to the Si lattice. This is compared with macroscopic continuum elasticity theory predictions for Ge/Si(001).

• Received 13 June 2002

DOI:https://doi.org/10.1103/PhysRevB.67.035404