1. Institute for Semiconductor Engineering, University of Stuttgart, 70569 Stuttgart, Germany
2. Centre of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal
3. CACTI, Univ. de Vigo, Campus Universitario Lagoas Marcosende 15, Vigo, Spain
4. IHP GmbH, Innovations for High Performance Microelectronics, Leibniz-Institut für innovative Mikroelektronik, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany
5. Dpto. Fisica Aplicada, Univ. de Vigo, Rua Maxwell s/n, Campus Universitario Lagoas Marcosende, Vigo, Spain