The Chinese University of Hong Kong
Advanced Graphene-based Optoelectronic Devices in the Near-Infrared and THz Spectral Ranges
J. B. Xu1, 2
1 Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, China
2 Materials Science and Technology Research Center, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, China
In this presentation, I will report on our recent progress in design, preparation and characterization of high-quality graphene-based optoelectronic devices.
At first, we present a high responsivity photodetector based on graphene-silicon heterostructure. In contrast to the previous graphene-silicon photodetector, we exploit the photoconductive mode in graphene, but in the Schottky contact against the silicon substrate, with the responsivity measured up to 1000A/W.
Secondly, we present two mechanisms to overcome the low optical absorption of graphene and the ultrashort life time of photo-induced carriers in graphene. One is from the vertical built-in field between the graphene and silicon, the other results from the plasmonic effect. Thanks to the above two mechanisms, a graphene-based short-wave infrared (SWIR) photodetector with high responsivity and fast photoresponse is designed. The responsivity of the proposed SWIR photodetector is measured up to a record of 83 A/W at the wavelength of 1.55 μm
Thirdly, we develop a high tunable THz phase modulator with the ultra-broadband based on phase transition effect under reflection, which is constructed by graphene and total internal reflection prism. Electrical gate voltage of -1.2 to 1.2 V operation on graphene enables the phase shift yielding up to 110 degree in the frequency range from 0.1 THz to 0.9 THz.
Fourthly, we propose a high performance solid-state modulator based on the Brewster reflection on graphene. Theoretically, reflection phase of electromagnetic wave (p-polarization) reflected from a media is zero or π, depending on the incident angle smaller or larger than the Brewster angle. We show that the Brewster angle of a media can be controlled by manipulating the conductivity of graphene placed on the media, as the incident angle of a THz wave can be arranged from a larger to a smaller one than the Brewster angle. By bearing this principle in mind, we design a solid-state, graphene-based phase modulator. Experimental results show that the phase of the reflected wave can be tuned from 0 to 90 degree in a frequency range from 0.1THz to 0.8THz.
This work is conducted in collaboration with Mr. Z. F. Chen,Drs. X. M. Wang, Z. Z. Cheng, L. Ye; Profs. H. K. Tsang, Emma MacPherson, E. Parrot; Mr. X. D. Liu, Mr. H. Li, et al. The work is in part supported by Research Grants Council of Hong Kong, particularly, via Grant Nos.AoE/P-02/12, 14207515, 14204616, and CUHK Group Research Scheme, as well as Innovation and Technology Commission ITS/096/14. J. B. Xu would like to thank the National Science Foundation of China for the support, particularly, via Grant No 61229401.
Dr. Xu received his B.Sc. and M.Sc. from Nanjing University in 1983 and 1986, respectively, in Physics and Electronic Science and Engineering, under the supervision of Prof. Shu-yi Zhang (Member of Chinese Academy of Sciences). Since 1988, he was highly privileged to study in the University of Konstanz (an elite university), particularly under the supervision of Prof. Klaus Dransfeld (Member of German Academy of Sciences), former Director of Max-Plank Institute for Solid State Research, and Max-Plank Institute for High-Magnetic Fields). His doctoral dissertation was focused on the near-field sensing and nanoscopic energy transfer and heat transport associated with electronic processes. He earned his doctorate (Dr.rer.nat.) in 1993. Afterwards, he joined the Department of Electronic Engineering, The Chinese University of Hong Kong. He has been Professor in the department since the midst of 2002.
Dr. Xu has published extensively on advanced electronic and photonic materials and devices as well as on nanotechnology in peer-reviewed professional journals (c.a. 240) and conferences (c.a. 50) as well as more than 200 presentations, including conference invited talks, colloquia, seminars, etc. The published papers have been extensively accessed and cited, as well as many topic reviews and monographs, and patents. Meanwhile, he has secured numerous competitive research grants. Also he actively participates in a myriad of professional activities and has served as symposium chair in several international conferences. Particularly, he has served as Member of International Advisory Committee, International Conference on Nanoscience and Technology, China 2009 (ChinaNano 2009), and as Director of Advanced Study Institute on Printed Electronics 2013 (Dedicated to Professor Sir Charles Kao on the Occasion of his 80th Birthday). He is Fellow of Hong Kong Institution of Engineers, Senior Member of IEEE, the Secretary and Council Member of Hong Kong Materials Research Society, and Member of American Physical Society, Materials Research Society, Hong Kong Institution of Science, and Physical Society of Hong Kong. Since 2007, he has been Director of Materials Science and Technology Research Center in CUHK. From 2011, he has been Convener of Strategic Initiatives for Nano, Energy, and Materials in CUHK.
Dr. Xu is a recipient of Joint Research Fund for Overseas Chinese, Hong Kong and Macau Scholars, funded by NSFC, a nationally prestigious award (formerly National Science Fund for Distinguished Young Scholars (Overseas Chinese)).