Gate-Controlled WSe2 Transistors Using a Buried Triple-Gate Structure.

In the present paper, we show tungsten diselenide (WSe2) devices that can be tuned to operate as n-type and p-type field-effect transistors (FETs) as well as band-to-band tunnel transistors on the same flake. Source, channel, and drain areas of the WSe2 flake are adjusted, using buried triple-gate substrates with three independently controllable gates. The device characteristics found in the tunnel transistor configuration are determined by the particular geometry of the buried triple-gate structure, consistent with a simple estimation of the expected off-state behavior.

Band-to-band tunneling in carbon nanotube field-effect transistors.

A detailed study on the mechanism of band-to-band tunneling in carbon nanotube field-effect transistors (CNFETs) is presented. Through a dual-gated CNFET structure tunneling currents from the valence into the conduction band and vice versa can be enabled or disabled by changing the gate potential. Different from a conventional device where the Fermi distribution ultimately limits the gate voltage range for switching the device on or off, current flow is controlled here by the valence and conduction band edges in a bandpass-filter-like arrangement. We discuss how the structure of the nanotube is the key enabler of this particular one-dimensional tunneling effect.

Multimode transport in Schottky-barrier carbon-nanotube field-effect transistors.

We present a detailed study on the impact of multimode transport in carbon nanotube field-effect transistors. Under certain field conditions electrical characteristics of tube devices are a result of the contributions of more than one one-dimensional subband. Through potassium doping of the nanotube the impact of the different bands is made visible. We discuss the importance of scattering for a stepwise change of current as a function of gate voltage and explain the implications of our observations for the performance of nanotube transistors.

Tunneling versus thermionic emission in one-dimensional semiconductors.

This Letter focuses on the role of contacts and the influence of Schottky barriers on the switching in nanotransistors. Specifically, we discuss (i) the mechanism for injection from a three-dimensional metal into a low-dimensional semiconductor, i.e., the competition between thermionic emission and thermally assisted tunneling, (ii) the factors that affect tunneling probability with emphasis on the importance of the effective mass for transistor applications, and (iii) a novel approach that enables determination of barrier presence and its actual height.

Field-modulated carrier transport in carbon nanotube transistors.

We have investigated the electrical transport properties of carbon nanotube field-effect transistors as a function of channel length, gate dielectric film thickness, and dielectric material. Our experiments show that the bulk properties of the semiconducting carbon nanotubes do not limit the current flow through the metal/nanotube/metal system. Instead, our results can be understood in the framework of gate and source-drain field induced modulation of the nanotube band structure at the source contact. The existence of one-dimensional Schottky barriers at the metal/nanotube interface determines the device performance and results in an unexpected scaling behavior.