Critical
issues in Ge/Si nanostructures: positioning, intermixing and ripening
The growth of Ge on Si surfaces proceeds according to the Stranski–Krastanow mode: after the formation of a 3–5 monolayer thick wetting layer, 3D islands nucleate to partially relieve the strain due to the 4.2% lattice mismatch. This growth mode is common in heteroepitaxy, and Ge–Si is a good model system for studying island growth in lattice–mismatched heterostructures [1]. We monitored the growth process in situ, taking Scanning Tunneling Microscopy and Low Energy Electron Microscopy (LEEM) movies. Critical issues include the controlled positioning of Ge/Si islands [2], Ge–Si interdiffusion processes [3], and ripening processes that affect islands after growth [4]. In this presentation I will address all three issues:
(i) By using step–bunched Si(111) surfaces as templates, we demonstrate the self–assembly of an ordered distribution of Ge islands without lithographic patterning [2].
(ii) Ge/Si intermixing has been shown to be significant [3], but the composition of single islands remains unknown. Here I describe Ge–Si intermixing from individual islands measured in situ using X–Ray Photoemission Electron Microscopy.
(iii) Finally, LEEM movies taken in situ during post–deposition annealing, reveal a surprising phenomenon of metastability [4].
References.
[1] F. Rosei, R. Rosei, Surf. Sci. 500, 395 (2002).
[2] A. Sgarlata, P.D. Szkutnik, A. Balzarotti, N. Motta, and F. Rosei, Appl. Phys. Lett., 83, 4002 (2003).
[3] F. Boscherini, G. Capellini, L. Di Gaspare, N. Motta, F. Rosei, S. Mobilio, Appl. Phys. Lett. 76, 682 (2000).
[4] F. Ratto, N. Motta, A. Sgarlata, P.D. Szkutnik, S. Cherifi, S. Heun, A. Locatelli, M. De Crescenzi, and F. Rosei, in preparation.