Available online at www.sciencedirect.com Physica E 17 (2003) 510–512 www.elsevier.com/locate/physe MBE grown Ge dots on Si/SiGe ion implanted buers P.I. Gaiduk * , A. Nylandsted Larsen, J. Lundsgaard Hansen Institute of Physics and Astronomy, University of Aarhus, NY Munkegade, DK-8000 Aarhus C, Denmark Abstract Stacks of six or eight bilayers of Ge/Si were grown by molecular beam epitaxy (MBE) on Si= Si0:5Ge0:5 buer layers modied with in situ implantation of 1 keV As + or Ge + ions. The structure was investigated by transmission electron microscopy (TEM). Vertically correlated Ge islands are observed by TEM. Results from variation of pre-implantation, thickness of Ge layers and temperature of MBE growth are presented. ? 2002 Elsevier Science B.V. All rights reserved. PACS: 68.65.Hb; 68.65.+g; 61.46.+w; 81.15.Hi; 68.55.Jk Keywords: Molecular beam epitaxy; Ge nanodots; Si–SiGe alloys There is considerable interest in self-assembled Ge nano-size islands (dots) on Si substrates both from fundamental and applicational points of view [1]. Self-assembled Ge quantum dots are usually grown via the Stranski–Krastanov growth mode, which starts rst with layer-by-layer growth followed by islands formation [2]. The main reason for islanding is the 4.16% mismatch between the Si and Ge lattice con- stants, thus a non-homogeneous strain distribution in the substrate eectively inuences on the formation of Ge dots. The latter has been repeatedly demon- strated using the elastic strain elds induced by dis- locations [3], by the pre-patterned surface [4], or by buried layers of Ge (SiGe) dots [5,6]. Recently, in situ implantation of As has been eectively applied for the modication of SiGe buer layers, to enhance the formation of vertical stacks of self-assembled Ge nanodots [6], or to grow novel, semi-spherical SiGe ∗ Corresponding author. Tel.: +89423723; fax: +86120740. E-mail address: gaiduk@ifa.au.dk (P.I. Gaiduk). nano-structures [7]. Also in these cases, the strain dis- tribution was discussed to be one of the reasons for enhanced Ge dot formation and vertical stacking of Ge dots. In the present work we report an enhancement of Ge dot formation in the case of Ge ion implanta- tion, and present observations of the inuence of Ge layer thickness and growth temperature on the MBE growth of vertically correlated Ge dots. The samples were grown by solid-source MBE us- ing e-beam evaporators for the Si and Ge deposition and a build-in low energy (1 keV) ion implanter for in situ incorporation of As or Ge. Wafers of p-type (0 0 1)Si were used as substrates. Following the SiO 2 desorption from the surface at 850 ◦ C, a 100 nm-thick Si buer layer was grown. Subsequently, a buer structure was grown at 525 ◦ C consisting of four alter- nating layers of 3 nm Si and 2:8 nm Si 0:5 Ge 0:5 . The growth temperature was controlled using both a py- rometer and a thermocouple, giving a temperature ac- curacy of about 15 ◦ . Typical growth rates were 0.084 and 0:1  A= s for the Si and Si 0:5 Ge 0:5 layers, respec- tively. During the growth of this four-layered buer 1386-9477/03/$ - see front matter ? 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S1386-9477(02)00854-8