1. Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
2. School of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853, USA
3. Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan
4. Department of Material Science and Engineering, Cornell University, Ithaca, New York 14853, USA
5. Terahertz Materials Analysis Center and Center for III-N technology, C3NiT – Janzèn, Department of Physics, Chemistry and Biology (IFM), Linköping University, 58183 Linköping, Sweden
6. Leibniz Institut für Polymerforschung e.V., 01069 Dresden, Germany