1. Department of Electrical and Computer Engineering, Boston University, 8 Saint Mary’s St., Boston, Massachusetts 02215, USA
2. Division of Materials Science and Engineering, Boston University, 15 Saint Mary’s St., Brookline, Massachusetts 02446, USA
3. Technology Innovation, OSRAM Opto Semiconductors, Beverly, Massachusetts 01915, USA
4. Department of Physics, Boston University, 590 Commonwealth Ave., Boston, Massachusetts 02215, USA