book of abstracts - IM2NP

A B S T R A C T S TUESDAY, JUNE 29 N A N O S E A 2 0 1 0
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9H10-9H30 Epitaxial SiGe self-assembled island growth by Surface Thermal Diffusion :
shape transition, intermixing and strain relaxation.
1 – Introduction
G.M. Vanacore1, M.Zani1, G. Isella2, J. Osmond2, E. Bonera3, F. Montalenti3, A.
Picco3, and A. Tagliaferri1 (1Dipartimento di Fisica, Politecnico di Milano, P.zza Leonardo da Vinci, 32-
20133 Milan, Italy 2L-NESS, Dipartimento di Fisica del Politecnico di Milano, Via Anzani 52, I-22100, Como, Italy
3Dipartimento di Scienza dei Materiali, and L-NESS, Università di Milano-Bicocca, via Cozzi 53, I-20125 Milano,
Italy)
Growth of Ge on Si surfaces has attracted much attention because of its importance both for the
semiconductor technology and for the comprehension of fundamental physical processes. The formation of
self-assembled SiGe islands is strongly dependent on the surface diffusion coefficient of Ge and Si atoms,
which rapidly vary with the temperature [1,2]. In this work, we present an experimental study by atomic
force microscopy, scanning Auger microscopy and micro-Raman spectroscopy of thermodynamically stable
SiGe islands epitaxially grown by surface thermal diffusion from a pure Ge stripe deposed on the Si(100)
surface.
2 – Abstract
Self-assembled islands with different faceting and dimensions varying over an order of magnitude are
produced by surface thermal diffusion of Ge at 600, 650 °C and 700 °C. They originate by the nucleation of
Ge atoms moving from artificially made nano-sized stripes used as sources of diffusion directly placed on
the sample surface. The total surface coverage of Ge strongly depends on the distance from the source stripe,
so that the method allows to investigate the island growth over a wide range of dynamical regimes. It is
shown that the region with highest Ge coverage (close to the stripe) presents the highest SiGe island density
and the lowest average island sizes, while where the coverage decrease to about 4 ML (farter away from the
stripe) the lowest density and the biggest average dimensions of the islands are attained, with a
correspondent shape evolution between smaller and larger islands. The statistics of the island population are
discussed within a semi-quantitative model of diffusion and nucleation. The model is based on few key
assumptions, in agreement with experimental [3-6] and theoretical [7] studies: an approximate exponential
form for the change in the chemical potential with the wetting layer thickness [8], a capture-zone growth
behaviour [9] and the competition between Ge and Si diffusion dynamics in determining the final Si content
of each island. Our results give experimental evidence that the island nucleation by surface thermal diffusion
evolves at microscopic level following a diffusion-limited growth mechanism, resulting in islands in their
thermodynamic equilibrium state. The role of Si incorporation and the plastic relaxation of single islands at
growth temperatures higher than 600 °C are experimentally investigated and critically discussed.
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