Theme 1: Nanoelectronics

Faculty

Eli Yablonovitch (theme leader), Berkeley
Jesus del Alamo, MIT
Felix Fischer, Berkeley
Ali Javey, Berkeley
Jing Kong, MIT
Steven Louie, Berkeley
Vladimir Stojanović, Berkeley

The Nanoelectronics research team aims to develop a highly energy efficient solid-state electronic switch as a replacement of the conventional transistor switch. The goal for this new switch is to operate in the milli-Volt range, at least two orders of magnitude lower than required in current transistors. Since the power goes as the voltage-squared, such a new switch would consume 10,000-times less power—the difference of charging your cell phone every day, or once every 30 years, for example.

In the last decade, considerable research efforts on alternate switching mechanisms have converged around the tunnel transistor, a device relying on the quantum-mechanical phenomenon of tunneling through energy barriers. The main reasoning behind tunnel transistors is that Moore’s Law will lead to devices so small as to require the consideration of tunneling in any case. So far, however, state-of-the-art device results of tunnel transistors have continued to be disappointing.

Two main tunnel modulation mechanisms are in play: tunnel-distance-modulation versus density-of-states modulation, which is also called energy filtering. The latter mechanism is considered to have the most potential to meet all device specifications. Emphasizing the Center’s goal to elucidate the underlying device physics, as opposed to simple device optimization, Theme I researchers found that the preferred density-of-states mechanism demands higher interface perfection than ever previously required in solid-state electronics.

Challenges

Tunneling is an interfacial process, limited by the two-dimensional density of quantum states, which is ~1012/(cm2 eV). This desirable tunneling needs to compete with bandgap defect state density, which is a famous figure-of-merit in electronics science. In the most favorable materials systems currently used the interfacial defect density is ~1010 /(cm2 eV). Therefore, even after decades of electronic material investigations, the best interface state-density materials are far from being good enough. The Center for E3S has thus embarked on a search for new material systems with interface property, beyond what decades of research have previously accomplished.

Current Projects

Two-dimensional Chalcogenide Semiconductor Materials

Two-dimensional chalcogenide semiconductor materials, in particular transition metal dichalcogenides (TMDCs), possess a layered structure, minimum surface roughness, and lack of dangling bonds and surface defects at extremely thin body (~1 nm for single layer). Furthermore, Center researchers have shown that the defect density of two-dimensional TMDC materials (for example, MoS2) can be further improved by orders of magnitude through chemical treatments that passivate or repair trap states, making them excellent candidates for low interfacial defect density materials.

Selected Recent Publications

Bottom-up Fabrication of Novel Semiconductors

Towards the goal of defect-free semiconductors, nanoelectronics researchers at E3S have recently embarked on bottom-up approaches in synthesizing semiconductors, versus the top-down approach in traditional semiconductor fabrication. Led by synthetic organic chemists within the Center, a synthesis strategy for the fabrication of defect-free semiconductors, hybrid graphene nanoribbons (GNRs) heterostructures, has been devised. The longer term goal is the development of synthetic tools, molecular building blocks, stabilization approaches, and purification techniques that will enable highly reproducible fabrication of stable GNR heterojunction devices for advanced circuit architectures.

Selected Recent Publications

III-V Nanowire Tunnel Field Effect Transistor

Nanowires of conventional III V semiconductors are excellent systems to explore the fundamental physics of tunneling devices. A major goal of the Center’s III-V nanowire TFET research is to identify the band-edge spectroscopic sharpness in a single-channel quantum wire configuration, where inhomogeneous broadening from doping, thickness fluctuation, would be absent owing to the presence of only a single quantum channel.

Selected Recent Publications