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Advances in Condensed Matter Physics
Volume 2012, Article ID 176053, 7 pages
http://dx.doi.org/10.1155/2012/176053
Research Article

Ge/Si Quantum Dots Superlattices Grown at Different Temperatures and Characterized by Raman Spectroscopy and Capacitance Measurements

1Department of Physics, Federal University of São Carlos, CP 676, 13565-905 São Carlos, SP, Brazil
2Institute of Semiconductor Physics, Novosibirsk 630090, Russia
3Institut für Physik, Technische Universität Chemnitz, 09107 Chemnitz, Germany

Received 28 March 2012; Accepted 31 July 2012

Academic Editor: Michael C. Tringides

Copyright © 2012 A. D. Rodrigues et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Ge/Si heterostructures with Ge self-assembled quantum dots (SAQDs) grown at various temperatures by molecular beam epitaxy were investigated using resonant Raman spectroscopy and capacitance measurements. The occurrence of quantum confinement effects was confirmed by both techniques. For the structures grown at low temperatures ( 3 0 0 βˆ’ 4 0 0 °C), the SAQDs optical phonon wavenumbers decrease as the Raman excitation energy is increased; this is an evidence of the scattering sensitivity to the size of the SAQDs and to the inhomogeneity in their sizes. However, the opposite behavior is observed for the SAQDs grown at higher temperatures, as a consequence of the competition between the phonon localization and internal mechanical stress effects. The 𝐸 1 electronic transition of the Ge in the SAQDs was found to be shifted towards higher energies as compared to bulk Ge, due to biaxial compressive stress and to the electronic confinement effect present in the structures. The intermixing of Si atoms in the quantum dots was found to be much more significant for the sample grown at higher temperatures. The capacitance measurements, besides confirming the existence of the dots in these structures, showed that the deepest Ge layers lose their 0D signature as the growth temperature increases.