1. Department of Microelectronics and Information Technology, Royal Institute of Technology, Electrum 229, 100 44 Kista, Sweden
2. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
3. Center for Solid State Electronics Research & Department of Electrical Engineering, Arizona State University, Tempe, Arizona, 85287‐6206, USA