Comparison between surfactant-mediated Bi/Ge/Si(1 1 1) epitaxy and Ge/Si(1 1 1) epitaxy Neelima Paul * , Hidehito Asaoka 1 , Bert Voigtla ¨nder Institut fu ¨r Schichten und Grenzfla ¨chen (ISG 3) and CNI––Center of Nanoelectronic Systems for Information Technology, Forschungszentrum Ju ¨lich, Leo-Brandt-Str., 52425 Ju ¨lich, Germany Received 17 November 2003; accepted for final publication 14 June 2004 Available online 14 July 2004 Abstract Using scanning tunneling microscopy (STM) the Ge epitaxy on a Bi terminated Si(1 1 1) surface is compared to the growth without surfactant. During the growth of the Ge wetting layer in surfactant mediated epitaxy (SME), Si and Ge can be distinguished by different apparent heights in the STM images due to the Bi termination of the surface. As soon as the two bilayer high wetting layer is completed, Ge islands with a flat top and an underlying dislocation network occur. Elastic distortions due to the dislocation network result in periodic sub-angstrom height undulations measured by the STM. In this case the Ge islands have the form of a mesa. With increasing Ge coverage, these mesas spread lat- erally. Beyond a Ge coverage of 10 bilayers, the Ge mesas have coalesced and further Ge deposition leads to a 2D layer- by-layer growth of Ge on Si(1 1 1). In epitaxy without the use of a surfactant as well, the formation of Ge islands with an underlying dislocation network is observed. However, in this case the Ge islands are much higher and show no tendency to coalesce. The partially relaxed islands coexist with another type of tall islands. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Scanning tunneling microscopy; Growth; Molecular beam epitaxy; Bismuth; Silicon; Germanium 1. Introduction The growth behavior of a thin germanium film on Si(1 1 1) has been and continues to be a subject of considerable interest in the field of surface science. Fundamental studies on strain relaxation are aptly suited for this simple system. The growth mode of such lattice mismatched (Ge having a lattice constant 4% larger than Si) 0039-6028/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2004.06.194 * Corresponding author. Tel.: +49 2461 618693; fax: +49 2461 613907. E-mail address: ne.paul@fz-juelich.de (N. Paul). 1 Permanent address: Neutron Science Research Center, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki 319-1195, Japan. Surface Science 564 (2004) 187–200 www.elsevier.com/locate/susc