Van der Waals Heterojunctions for Energy-Efficient Electronics

Abstract:

Two-dimensional materials show immense potential as successor to silicon for next generation electronics. Graphene, being semi-metallic, can be used as electrodes and interconnects and in transistors for analog applications. Hexagonal boron nitride is an insulator with a low dielectric constant. The versatile platform of transition metal dichalcogenides (TMDCs) offers semiconductors - with a range of bandgaps, also tunable with their number of layers, Mott insulators, semimetals, and superconductors. These materials, with surfaces free of native oxide and dangling bonds and precisely controllable thicknesses down to one atomic layer, exhibit excellent transport characteristics at regimes where conventional semiconductors would fail. These 2D materials can be stacked on one another seamlessly, without any lattice mismatch. The van der Waals (vdW) bonding leads to sharp interfaces without any interdiffusion of atoms. Thus, vdW heterojunctions can be used for a wide variety of applications, ranging from steep transistors, gate-tunable diodes, to non-volatile memory devices and tunable light emitting diodes. 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. 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 for the continued betterment of human lives.

Biography:

Tania Roy 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 has been working 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.