Self-Aligned Top-Gate Structure in High-Performance 2D p-FETs via van der Waals Integration and Contact Spacer Doping.

The potential of 2D materials in future CMOS technology is hindered by the lack of high-performance p-type field effect transistors (p-FETs). While utilization of the top-gate (TG) structure with a p-doped spacer area offers a solution to this challenge, the design and device processing to form gate stacks pose serious challenges in realization of ideal p-FETs and PMOS inverters. This study presents a novel approach to address these challenges by fabricating lateral p-p-p junction WSe FETs with self-aligned TG stacks in which desired junction is formed by van der Waals (vdW) integration and selective oxygen plasma-doping into spacer regions.

Gate-Modulated Ultrasensitive Visible and Near-Infrared Photodetection of Oxygen Plasma-Treated WSe Lateral pn-Homojunctions.

We investigate the development of gate-modulated tungsten diselenide (WSe)-based lateral pn-homojunctions for visible and near-infrared photodetector applications via an effective oxygen (O) plasma treatment. O plasma acts to induce the p-type WSe for the otherwise n-type WSe by forming a tungsten oxide (WO) layer upon O plasma treatment. The WSe lateral pn-homojunctions displayed an enhanced photoresponse and resulted in open-circuit voltage () and short-circuit current () originating from the pn-junction formed after O plasma treatment.

Metallic contact induced van der Waals gap in a MoS FET.

Electrical metal contacts formed with 2D materials strongly affect device performance. Here, we used scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS) to characterize the interfacial structure formed and physical damage induced between MoS2 and the most commonly used metals, Ti, Cr, Au, and Pd. We further correlated the electrical performance with physical defects observed at the 2D interfacial structure.

The device level modulation of carrier transport in a 2D WSe field effect transistor via a plasma treatment.

Tungsten diselenide (WSe) has received significant attention because it shows the pristine ambipolar property arising from the Fermi level located near the midgap and can be converted to uni-polar form. In this study, we observe the formation of tungsten oxide (WO) on the WSe surface after oxygen plasma treatment and show that the p-type WO dopes WSe. In our devices that underwent plasma treatment, it was interesting to find a strong correlation between the changes in the work function of WSe and a gold electrode, and the channel and contact resistances.

Colossal grain growth yields single-crystal metal foils by contact-free annealing.

Single-crystal metals have distinctive properties owing to the absence of grain boundaries and strong anisotropy. Commercial single-crystal metals are usually synthesized by bulk crystal growth or by deposition of thin films onto substrates, and they are expensive and small. We prepared extremely large single-crystal metal foils by "contact-free annealing" from commercial polycrystalline foils.

Modulation of Quantum Tunneling via a Vertical Two-Dimensional Black Phosphorus and Molybdenum Disulfide p-n Junction.

Diverse diode characteristics were observed in two-dimensional (2D) black phosphorus (BP) and molybdenum disulfide (MoS) heterojunctions. The characteristics of a backward rectifying diode, a Zener diode, and a forward rectifying diode were obtained from the heterojunction through thickness modulation of the BP flake or back gate modulation. Moreover, a tunnel diode with a precursor to negative differential resistance can be realized by applying dual gating with a solid polymer electrolyte layer as a top gate dielectric material.

Fermi Level Pinning at Electrical Metal Contacts of Monolayer Molybdenum Dichalcogenides.

Electrical metal contacts to two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs) are found to be the key bottleneck to the realization of high device performance due to strong Fermi level pinning and high contact resistances (R). Until now, Fermi level pinning of monolayer TMDCs has been reported only theoretically, although that of bulk TMDCs has been reported experimentally. Here, we report the experimental study on Fermi level pinning of monolayer MoS and MoTe by interpreting the thermionic emission results.