PhD Defense: "Two-Dimensional Electronic Materials and Devices – Opportunities and Challenges"

Jiahao Kang

August 24th (Thursday), 10:00am
Elings Hall (CNSI), Rm 3001

The unprecedented growth of Internet of Things (IoT) and the 4th Industrial Revolution (Industry 4.0) not only demands dimensional scaling of device technologies but also new types of applications beyond today’s electronics. Two-dimensional (2D) materials, a group of layered crystals (such as graphene and MoS2) with unique properties, have emerged as promising candidates for IoT/Industry 4.0 electronics since they can not only extend the scaling with unprecedented performance and energy efficiency but also exhibit high potential for novel devices. However, such nanomaterials suffer from significant challenges for device applications, especially in the formation of interfaces with conventional bulk materials. My doctoral dissertation has been focused on solving those fundamental issues (such as contacts, interfaces and doping) and identifying applications uniquely enabled by 2D materials.

First, I will present my work on metal contacts to 2D semiconductors, which has been a huge hurdle for 2D transistor technologies. In my pioneering study, new interface physics originating from the unique dimensionality and surface properties have been revealed [IEDM 2012]. I will describe solutions to minimize contact resistance though techniques of hybridization [Phys. Rev. X 2014] and seamless contacts [APL 2013; Nature Materials 2015]. These techniques transform 2D semiconductors from solely scientifically-interesting materials into high-performance field-effect transistor (FET) technologies, such as MoS2 FETs with record-low contact resistances [IEDM 2013; APL 2014] and the first demonstration of monolayer n-type WSe2 FETs with record-high drive current and mobility [Nano Lett. 2013].

Beyond metal interfaces, a comprehensive computational study for dielectric interface has been conducted, which is crucial for preserving the 2D carrier mobility [SISC 2014]. Moreover, the vertical van der Waals interfaces between 2D and 3D semiconductors, have been studied and exploited into a novel beyond-silicon transistor technology – the first 2D channel tunnel FET [Nature 2015] demonstrated by our group, which beat the fundamental limitation in the switching behavior of transistors. I will describe recent results from the engineering of such 2D-3D semiconductor interfaces by surface reduction /passivation, exhibiting a significant boost in tunneling currents.

While conventional diffusion/ion implantation methods are infeasible for 2D materials, I will present two specific doping techniques for 2D materials – surface doping [Nano Lett. 2015; Nature Nano. 2016] and intercalation doping [EDL 2016], the latter of which has been employed to demonstrate the first graphene interconnects with excellent performance, reliability and energy-efficiency by our group [Nano Lett. 2016; IRPS 2016].

Finally, by uniquely exploiting the high kinetic inductance and conductivity of intercalation doped graphene, a fundamentally different on-chip inductor technology has been demonstrated [IEDM 2014; Nature Electronics (under review)], with both small form-factors and high inductance density, that were once thought unachievable in tandem. This 2D technique provides an attractive solution to the longstanding scaling problem of analog/RF electronics and opens up an unconventional pathway for the development of future ultra-compact wireless communication systems. I will conclude by providing my vision for how a ‘smart life’ can be realized in future by harnessing the capabilities of various 2D technologies in the era of IoT and Industry 4.0.

About Jiahao Kang:

Jiahao Kang Jiahao Kang is a Ph.D. Candidate and Graduate Student Researcher in the Nanoelectronics Research Laboratory (NRL), Department of Electrical and Computer Engineering at University of California, Santa Barbara, CA, advised by Prof. Kaustav Banerjee. His doctoral research has played a pioneering role in the understanding of interfaces to 2D materials, leading to a number of breakthrough device innovations in NRL, uniquely enabled by 2D materials. He has authored or coauthored nearly 50 peer-reviewed publications in high-impact journals and highly-selective conferences (such as Nature, Nature Materials, Nature Nano., Nano Lett., IEEE EDL, Phys. Rev. X, APL and IEDM), which have received over 1,500 citations (as of Aug. 2017) with an h-index of 17. For his significant research contributions and academic excellence, he was awarded the 2016 Peter J. Frenkel Foundation Fellowship from UCSB’s Institute for Energy Efficiency, as well as the prestigious IEEE Electron Devices Society PhD Fellowship in 2016 as the only recipient from the entire Americas.

Hosted by: Professor Kaustav Banerjee