Key role of the wetting layer in revealing the hidden path of Ge/Si(001) Stranski-Krastanow growth onset
- Institute of Semiconductor and Solid State Physics, Johannes Kepler University, A-4040 Linz (Austria)
- L-NESS and Materials Science Department, University of Milano-Bicocca, I-20125 Milano (Italy)
- Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States)
The commonly accepted Stranski-Krastanow model, according to which island formation occurs on top of a wetting layer (WL) of a certain thickness, predicts for the morphological evolution an increasing island aspect ratio with volume. We report on an apparent violation of this thermodynamic understanding of island growth with deposition. In order to investigate the actual onset of three-dimensional islanding and the critical WL thickness in the Ge/Si(001) system, a key issue is controlling the Ge deposition with extremely high resolution [0.025 monolayer (ML)]. Atomic force microscopy and photoluminescence measurements on samples covering the deposition range 1.75-6.1 ML, taken along a Ge deposition gradient on 4 in. Si substrates and at different growth temperatures (T{sub g}), surprisingly reveal that for T{sub g}>675 deg. C steeper multifaceted domes apparently nucleate prior to shallow (105)-faceted pyramids, in a narrow commonly overlooked deposition range. The puzzling experimental findings are explained by a quantitative modeling of the total energy with deposition. We accurately matched ab initio calculations of layer and surface energies to finite-element method simulations of the elastic energy in islands, in order to compare the thermodynamic stability of different island shapes with respect to an increasing WL thickness. Close agreement between modeling and experiments is found, pointing out that the sizeable progressive lowering of the surface energy in the first few MLs of the WL reverts the common understanding of the SK growth onset. Strong similarities between islanding in SiGe and III/V systems are highlighted.
- OSTI ID:
- 21294481
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 80, Issue 20; Other Information: DOI: 10.1103/PhysRevB.80.205321; (c) 2009 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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