1. Solid State Electronics Laboratory, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109-2122, USA
2. Center for High Technology Materials, Department of Electrical Engineering and Computer Engineering, University of New Mexico, Albuquerque, NM 87106, USA
3. Sensors and Electron Devices Directorate, US Army Research Laboratory, Adelphi, Maryland 20783, USA