1. Semiconductor Materials Division Department of Physics, Chemistry and Biology-IFM Linköping University S-58183 Linköping Sweden
2. Nanoscale Engineering Division Department of Physics, Chemistry and Biology-IFM Linköping University S-58183 Linköping Sweden
3. Institute of Electronics Bulgarian Academy of Sciences 72 Tzarigradsko Chaussee Blvd 1784 Sofia Bulgaria