1. National Microelectronics Research Centre, University College Cork, Lee Maltings, Prospect Row, Cork, Ireland
2. Laboratory of Solid State Physics (LPST), UMR 5477, Paul Sabatier University, 118 route de Narbonne, 31062 Toulouse Cedex 04, France
3. VTT Centre for Microelectronics, Tietotie 3, 02150 Espoo, Finland