1. Department of Physics Capital Normal University; Beijing Key Lab for Terahertz Spectroscopy and Imaging and Key Laboratory of Terahertz Optoelectronics Ministry of Education; Beijing; 100048; PR China
2. State Key Laboratory for Integrated Optoelectronics; Institute of Semiconductors Chinese Academy of Sciences; Beijing; 100083; PR China
3. Institute of Experimental Physics I; Justus-Liebig University; Heinrich-Buff-Ring 16; 35392; Giessen; Germany