1. Indian Institute of Technology Kanpur, Kanpur 208016, India
2. Department of Physics, National University of Singapore, 3 Science Drive 3, Singapore 117542, Singapore
3. Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India
4. SZU-NUS Collaborative Innovation Centre for Optoelectronic Science & Technology and Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen, Guangdong 518060, China