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Abstract
The original version of this Article omitted an acknowledgement to the source of Fig. 1a. The following has been added to the end of the caption to Fig. 1: ‘Figure 1a adapted from ref. 13 (copyright 2016 Macmillan Publishers)’. This has been corrected in the PDF and HTML versions of the Article.
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1 Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China; College of Applied Sciences, Beijing University of Technology, Beijing, China
2 Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China; College of Materials Science and Opto-electronic Technology, University of Chinese Academy of Sciences, Beijing, China
3 College of Applied Sciences, Beijing University of Technology, Beijing, China
4 Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China