1. Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
2. U.S. Naval Research Laboratory, Washington, DC 20375, USA
3. Terahertz Materials Analysis Center and Competence Center for III-Nitride Technology C3NiT—Janzén, Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping SE 58183, Sweden
4. J. A. Woollam Co., Lincoln, Nebraska 68508, USA
5. Leibniz Institute for Polymer Research, Dresden D 01069, Germany