1. School of Electrical and Computer Engineering, University of Campinas, 13083-852 Campinas-SP, Brazil
2. Center for Semiconductor Components and Nanotechnologies, University of Campinas, 13083-870 Campinas-SP, Brazil
3. Institute of Physics Gleb Wataghin, University of Campinas, 13083-859 Campinas-SP, Brazil
4. Formerly with Soitec, Parc Technologique des Fontaines, 38190 Bernin, France
5. Institut für Mathematik und Naturwissenschaften, Fachhochschule Nordwestschweiz, CH-5210 Windisch, Switzerland