1. Department of Semiconductor Materials Engineering Wrocław University of Science and Technology Wybrzeże Wyspiańskiego 27 Wrocław 50-370 Poland
2. Electrical and Computer Engineering Cornell University Ithaca NY 14853 USA
3. Applied and Engineering Physics Cornell University Ithaca NY 14853 USA
4. Material Science and Engineering Cornell University Ithaca NY 14853 USA
5. Kavli Institute of Nanoscale Science Cornell University Ithaca NY 14853 USA