SUTD Scientists Solve a Long-standing Theoretical Problem in 2D Material Electronics

Significance 

A Schottky diode is an electronic component that primarily consists of a semiconductor-metal junction. This diode, unlike a normal semiconductor diode, can be turned on and off very quickly. When a 2D material is brought into contact with a bulk material or another 2D material, a 2D-material-based Schottky heterostructure is formed. Formation of such heterostructures is an inevitable process in many optoelectronics and nano-electronics applications. Over the years, 2D-material-based Schottky heterostructures have garnered considerable research attention owing to their wide applicability in various fields. Unfortunately, several discrepancies and misperceptions regarding their carrier transport physics still persist in literature. Although recent works have shed light on the growth, structural, thermal, electrostatic, electronic, and electrical properties of 2D-material-based lateral Schottky heterostructure, a consistent model remains lacking.

In line with this, Dr. Yee Sin Ang , Professor Hui Ying Yang and Professor Lay Kee Ang from the SUTD-MIT International Design Center & Science and Math Cluster at Singapore University of Technology and Design (SUTD) developed generalized analytical reversed saturation current (RSC) models for lateral Schottky heterostructure (LSH) and vertical Schottky heterostructure (VSH) over a wide range of 2D electronic systems, including nonrelativistic electron gas, Rashba spintronic systems, single- and few-layer graphene, and thin films of topological solids. Their model anticipated that the 2D-material-based LSH and VSH are governed by completely different charge transport equations, which can be characterized by a simple universal scaling exponent. Their work is currently published in the research journal, Physical Review Letters.

The research method employed considered a 2D nanosheet in contact with a bulk or 2D semiconductor via its edge to form LSH or via its planar surface to form VSH. Next, a generalized analytical RSC model for LSH and VSH was developed. Finally, the researchers demonstrated that the generalized model is directly applicable for a large variety of 2D electronic systems.

The authors observed that the classic diode scaling of β=2 for a nonrelativistic electrons in bulk material was no longer valid for 2D materials. As a consequence, they developed universal scaling laws which provided a simple useful tool for the analysis of carrier transport and for the extraction of Schottky barrier height in 2D material Schottky heterostructures. Lastly, based on the experimental results of the graphene-based vertical Schottky heterostructure, they noted that the β=1 scaling provided a better fitting with the experimental data as compared to that of the classic β=2 scaling.

In a nutshell, the SUTD study demonstrated the emergence of a universal scaling exponent β=3/2 in LSH, and β=1 in VSH with scattering-induced momentum non-conservation effect. They noted that their model had resolved some of the conflicting results from prior works and was in agreement with recent experiments. Altogether, the findings reported by SUTD scientists have the potential to provide a simple theoretical tool for the description of 2D-material-based heterostructures, thus paving the way for both a fundamental understanding of nanoscale interface physics and applied device engineering.

The new theory has far reaching impact in solid state physics,” said principal investigator of this research, Prof. Lay Kee Ang, “It signals the breakdown of classic diode equation widely used for traditional materials over the past 60 years, and shall improve our understanding on how to design better 2D material electronics.”

SUTD Scientists Solve a Long-standing Theoretical Problem in 2D Material Electronics - Advances Engineering

 

About the author

Yee Sin Ang is a research fellow at the Singapore University of Technology and Design (SUTD). He obtained a Bachelor of Medical and Radiation Physics (2010) and a Ph.D. in theoretical condensed matter physics (2014) from the University of Wollongong, Australia.

His research mainly focuses on the theory of electron transport and emission in 2D materials and interfaces, quantum transport in superconducting and topological systems, 2D material valleytronics, and the device physics of electronics, photonics and optoelectronics. He is also interested in the modeling of complex systems such as disordered semiconductor, city and fractal objects. His research has received awards including Faculty Best Thesis Prize (Australia, 2015), IPS Meeting Outstanding Poster Award (Singapore, 2016), and FIRST Industry Workshop First Prize Winner (Singapore, 2017).

About the author

Associate Prof. Hui Ying Yang is currently an Associate Professor at the Singapore University of Technology and Design (SUTD). She received her Ph.D. from Nanyang Technological University, Singapore. Afterward, she was appointed to the position of Assistant Professor in 2010 in SUTD and promoted to Associate Professor in 2016. She was also a Singapore Millennium Foundation Fellow (Nanyang Technological University , 2006 – 2008), Lee Kuan Yew Fellow (Nanyang Technological University, 2008 – 2010), and a Visiting Professor to the Massachusetts Institute of Technology (MIT) in 2011.

Her current research mainly focuses on the design and fabrication of low-dimensional nanomaterials, carbon nanomaterials based water treatment process, and novel materials and devices for electrochemical energy storage. She has received awards such as IPS Nanotechnology Medal (Singapore, 2018), SUTD Research Excellence Award (Singapore, 2015), Nanonica Prize (EU, 2014), Outstanding Young Manufacturing Engineer Award (USA, 2014), MCCC-AAET Green Award, Singapore Winner and Grand Winner (Malaysia, 2013), IES Prestigious Engineering Achievement Awards (Singapore, 2013), Tan Kah Yee Inventors Award (Singapore, 2013), First Prize in MRS Science-as-Art Competition (USA, 2013), and L’Oreal Singapore for Women in Science National Fellowships (Singapore, 2010).

About the author

Prof. Ricky Lay Kee Ang received the B.S. degree from National Tsing Hua University, Taiwan (1994) and the M.S. and Ph.D. degrees from the Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, USA, in 1996 and 1999, respectively. He received a fellowship to work as a Los Alamos National Laboratory Director Postdoctoral Fellow in the Plasma Physics Applications Group, Applied Physics Division, from 1999 to 2001. He was an Assistant Professor and a tenured Associate Professor in the Division of Microelectronics, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, from 2001 to 2011. He joined the Singapore University of Technology and Design (SUTD) in 2011, and is currently the Head of Science and Math Cluster and the Interim Head of the Engineering Product Development Pillar. He is appointed as Ng Teng Fong Chair Professor for the SUTD-ZJU Innovation, Design, and Entrepreneurship Alliance, since 2016.

His research interests include electron emission and transport in novel materials, electrical contact and its charge transport, Dirac material based devices, and the computational methods of complex systems using fractal model. He was the founding Chairman of the IEEE NPSS chapter in Singapore in 2012. He received several Window of Science Awards from AFOSR-AOARD (2007, 2012, 2015, 2017), USA ONR Global Visiting Scientist Award (2009, 2017), The Public Administration (Bronze) Medal by Singapore Government (2017) and SUTD Excellent Faculty Award (2015).

Reference

Yee Sin Ang, Hui Ying Yang, L. K. Ang. Universal Scaling Laws in Schottky Heterostructures Based on Two-Dimensional Materials. Physical Review Letters, volume 121, 056802 (2018)

Go To Physical Review Letters

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