1. Chair of Electronic Devices, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, Germany
2. Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, 3688 Nanhai Avenue, 518060 Shenzhen, P. R. China
3. Chair of Novel Manufacturing Techniques and Materials, University of Wuppertal, Bahnhofstr. 15, 42651 Solingen, Germany