1. School of Optical and Electronic Information Huazhong University of Science and Technology Wuhan 430074 P. R. China
2. Department of Electrical Engineering and Computer Sciences University of California Berkeley CA 94720 USA
3. School of Materials Science and Energy Engineering Foshan University Foshan Guangdong 528000 P. R. China
4. The Molecular Foundry Lawrence Berkeley National Lab Berkeley CA 94720 USA
5. Department of Electrical and Computer Engineering University of Miami Coral Gables FL 33146 USA