1. Consiglio Nazionale delle Ricerche (CNR) − Istituto per la Microelettronica e Microsistemi (IMM), Strada VIII, n. 5 - Zona Industriale, I-95121 Catania, Italy
2. STMicroelectronics Stradale Primosole, 50 - Zona Industriale, I-95121 Catania, Italy
3. Department of Physics and Astronomy, University of Catania, Via Santa Sofia 64, I-95123 Catania, Italy
4. Department of Physics and Chemistry Emilio Segrè, University of Palermo, via Archirafi 36, I-90123 Palermo, Italy
5. ATEN Center, University of Palermo, Viale delle Scienze Ed. 18, I-90128 Palermo, Italy