Van der Waals Heterojunctions for Energy-efficient Electronics

Tania Roy, Ph.D.
NanoScience Technology Center, University of Central Florida
PSB 160/161, 4:00-5:00pm

Abstract: Two-dimensional materials show immense potential as successor to silicon for next generation electronics. The family of 2D materials allows a wide range of bandgaps to select from. The ability to stack these 2D materials without any lattice mismatch allows easy construction of vertical van der Waals (vdW) heterostructures. A naturally passivated surface without dangling bonds helps in integration with photonic structures such as waveguides and cavities. Despite being atomically thin, many 2D materials interact strongly with light. Amazingly enough, defects in these monolayers can be chemically passivated to enhance luminescence efficiency close to 100%. From gapless graphene to direct band-gap monolayer semiconducting transition metal dichalcogenides (TMDCs), these 2D materials allow for the realization of various nanophotonic devices and the exploration of fundamental optical sciences, covering a wide spectral range from the microwave to the ultraviolet.

In this talk, a vdW heterojunction-based all-two-dimensional transistor will be discussed. The all-2D transistor shows no surface roughness scattering, a property hitherto unforeseen in its three dimensional counterparts. A dual-gated MoS2/WSe2 vdW heterojunction diode can be tuned to operate in various diode operation regimes. The same device operates as a forward rectifying diode as well as a tunnel diode, merely by application of gate voltage. The first observation of gate controlled band to band tunneling in semiconducting 2D heterostructures was made here, enhancing the prospects of using vdW heterojunctions for low power electronic applications. The tunability of band alignment opens up prospects of using this system for a gate-tunable light emitting diode. A 2D/2D tunnel field effect transistor with WSe2 and SnSe2 will be discussed. VdW heterojunctions with graphene/h-BN/graphene show negative differential resistance, which can be used in analog applications, such as in oscillators and amplifiers. Also, a graphene/insulator/graphene heterostructure demonstrates resistive switching and can be used to make ultra-low power resistive memories. Thus, vdW heterojunctions display a new paradigm of materials innovation to sustain the aggressive improvement of electronics and optoelectronics for the continued betterment of human lives.


Biography: Tania Roy is an Assistant Professor at the NanoScience Technology Center at UCF since July 2016. She received B.E. (Hons.) in Electrical and Electronics Engineering from B.I.T.S. Pilani, India in 2006. She obtained her Ph.D degree in Electrical Engineering from Vanderbilt University, TN in December 2011, where she worked on the reliability of GaN/AlGaN high electron mobility transistors for high power and high frequency electronics. Following that, she worked as a postdoctoral fellow at Georgia Institute of Technology on graphene-based devices for low power applications till 2013. She joined University of California, Berkeley as a postdoc in 2014 where she worked on two-dimensional materials for future generation electronics. She made the world’s first all-two-dimensional transistor, and reported the first gate controlled Esaki diode with van der Waals heterojunctions. Her research interests include using novel functional materials for energy-efficient electronics and optoelectronics.