Islands as catalyst for film relaxation in Bi-mediated Ge epitaxy on Si 111/

The growth of Ge on Bi-terminated Si 111.63=63 has been investigated by scanning tunneling microscopy STM.and X-ray standing waves XSW.. In the Ge thickness range from 1 to 15 bilayers BL., the morphology of the Ge film surface undergoes drastic changes. At low coverages, a smooth layer-by-layer growth mode of pseudomorphically strained Ge is found. Further Ge deposition leads to the formation of clusters of triangular partially relaxed Ge islands with a side length of approximately 200 A°and an average island height of approximately 20 A°. The islands act as catalyst for further island formation and for the relaxation of the complete Ge film by dislocation formation. Finally with increasing Ge film thickness, the surface morphology changes again. Ge films exceeding a thickness of ;8 BL are almost completely relaxed and smooth. Hence, Bi can be concluded to successfully act as a surfactant for Ge epitaxy on Si 111.. q2000 Elsevier Science B.V. All rights reserved.