1. Department of Physics, NC State University, Raleigh, North Carolina 27695, USA
2. Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215, USA
3. Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA
4. Photonics Center, Boston University, Boston, Massachusetts 02215, USA
5. Organic and Carbon Electronics Lab (ORaCEL), NC State University, Raleigh, North Carolina 27695, USA