[1] Univ Montpellier 2, Etud Semicond Grp, CNRS, UMR 5650,CC 074, F-34095 Montpellier 5, France
[2] Univ Aveiro, CICECO, Dept Phys, P-3810193 Aveiro, Portugal
[3] Notre Dame Univ, Dept Elect Comp & Commun Engn, Deir El Kamar 5725, Lebanon
[4] Tech Univ Ilmenau, FG Nanotechnol, Ctr Micro & Nanotechnol, D-98684 Ilmenau, Germany