Strain relaxation during the surfactant modified epitaxial growth of Ge/Si(001)

• Published in: Surface science 1992-06, Vol.273 (1), p.1-8
• Main Authors: Thornton, J.M.C., Williams, A.A., Macdonald, J.E., van Silfhout, R.G., Finney, M.S., Norris, C.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Physics; Solid surfaces and solid-solid interfaces; Surface and interface dynamics and vibrations; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/0039-6028(92)90270-G

The initial strain relaxation of Ge on Si(001) has been investigated during epitaxial growth modified by a “surfactant” layer of Sb. Grazing-incidence X-ray diffraction was used to measure the strain relaxation due to its high sensitivity to the in-plane distribution of lattice spacings. We have observed the critical thickness for strain relaxation in the Ge overlayer to be ~ 11 monolayers (ML), with further relaxation developing gradually and in stages. A meta-stable, partially relaxed layer forms up to a coverage of ~ 30 ML, after which a more pronounced relaxation takes place. Even at a coverage of ~ 55 ML, complete strain relief has not been reached, and was only achieved after a 700°C thermal anneal. Concurrent specular reflectivity measurements also reveal that the Ge overlayer grows in a layer-by-layer fashion, and not in the Stranski-Krastanow mode expected for the Ge/Si system. These data show dramatically how the modification of surface energies through the presence of a “surfactant” can affect the morphology of, and strain in, a lattice-mismatched heteroepitaxial system.