1. School of Physics, Engineering and Technology, University of York, York YO10 5DD, U.K.
2. São Carlos School of Engineering, Department of Electrical and Computer Engineering, University of São Paulo, São, Carlos-SP 13566-590, Brazil
3. School of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853, United States
4. AIXTRON SE, Dornkaulstraße. 2, Herzogenrath 52134, Germany