1. Department of Photonics and Nanoelectronics, BK 21 FOUR ERICA-ACE Center, Hanyang University, Ansan 15588, Korea
2. School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea
3. Center for Opto-Electronic Materials and Devices, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea
4. Department of Applied Physics, Center for Bionano Intelligence Education and Research, Hanyang University, Ansan 15588, Korea