Monolayer WSe Field-Effect Transistor Performance Enhancement by Atomic Defect Engineering and Passivation.

Monolayer two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged as leading candidates for next-generation electronic devices beyond silicon, owing to their atomically thin structure and superior electrostatic control. However, their integration into industrial applications remains limited due to high densities of lattice defects and challenges in achieving stable and effective doping. In this work, we present a passivation and doping technique that significantly recovers and enhances the electrical properties of monolayer tungsten diselenide (WSe).

Fundamental Understanding of Interface Chemistry and Electrical Contact Properties of Bi and MoS.

The interface properties and thermal stability of bismuth (Bi) contacts on molybdenum disulfide (MoS) shed light on their behavior under various deposition conditions and temperatures. The examination involves extensive techniques including X-ray photoelectron spectroscopy, scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS). Bi contacts formed a van der Waals interface on MoS regardless of deposition conditions, such as ultrahigh vacuum (UHV, 3 × 10 mbar) and high vacuum (HV, 4 × 10 mbar), while the oxidation on MoS has been observed.

On-Chip Synthesis of Quasi-2D Semimetals from Multi-Layer Chalcogenides.

Reducing the dimensions of materials from three to two, or quasi-two, provides a fertile platform for exploring emergent quantum phenomena and developing next-generation electronic devices. However, growing high-quality, ultrathin, quasi2D materials in a templated fashion on an arbitrary substrate is challenging. Here, the study demonstrates a simple and reproducible on-chip approach for synthesizing non-layered, nanometer-thick, quasi-2D semimetals.

Experimental demonstration of an on-chip p-bit core based on stochastic magnetic tunnel junctions and 2D MoS transistors.

Probabilistic computing is a computing scheme that offers a more efficient approach than conventional complementary metal-oxide-semiconductor (CMOS)-based logic in a variety of applications ranging from optimization to Bayesian inference, and invertible Boolean logic. The probabilistic bit (or p-bit, the base unit of probabilistic computing) is a naturally fluctuating entity that requires tunable stochasticity; by coupling low-barrier stochastic magnetic tunnel junctions (MTJs) with a transistor circuit, a compact implementation is achieved. In this work, by combining stochastic MTJs with 2D-MoS field-effect transistors (FETs), we demonstrate an on-chip realization of a p-bit building block displaying voltage-controllable stochasticity.

Tailoring amorphous boron nitride for high-performance two-dimensional electronics.

Two-dimensional (2D) materials have garnered significant attention in recent years due to their atomically thin structure and unique electronic and optoelectronic properties. To harness their full potential for applications in next-generation electronics and photonics, precise control over the dielectric environment surrounding the 2D material is critical. The lack of nucleation sites on 2D surfaces to form thin, uniform dielectric layers often leads to interfacial defects that degrade the device performance, posing a major roadblock in the realization of 2D-based devices.

High-Performance Complementary Circuits from Two-Dimensional MoTe.

Two-dimensional (2D) materials hold great promise for future complementary metal-oxide semiconductor (CMOS) technology. However, the lack of effective methods to tune the Schottky barrier poses a challenge in constructing high-performance complementary circuits from the same material. Here, we reveal that the polarity of pristine MoTe field-effect transistors (FETs) with minimized air exposure is n-type, irrespective of the metal contact type.

Statistical Assessment of High-Performance Scaled Double-Gate Transistors from Monolayer WS.

Scaling of monolayer transition metal dichalcogenide (TMD) field-effect transistors (FETs) is an important step toward evaluating the application space of TMD materials. Although some work on ultrashort channel monolayer (ML) TMD FETs has been published, there exist no comprehensive studies that assess their performance in a statistically relevant manner, providing critical insights into the impact of the device geometry. Part of the reason for the absence of such a study is the substantial variability of TMD devices when processes are not carefully controlled.

Mobility Extraction in 2D Transition Metal Dichalcogenide Devices-Avoiding Contact Resistance Implicated Overestimation.

Schottky barrier (SB) transistors operate distinctly different from conventional metal-oxide semiconductor field-effect transistors, in a unique way that the gate impacts the carrier injection from the metal source/drain contacts into the channel region. While it has been long recognized that this can have severe implications for device characteristics in the subthreshold region, impacts of contact gating of SB in the on-state of the devices, which affects evaluation of intrinsic channel properties, have been yet comprehensively studied. Due to the fact that contact resistance (R ) is always gate-dependent in a typical back-gated device structure, the traditional approach of deriving field-effect mobility from the maximum transconductance (g ) is in principle not correct and can even overestimate the mobility.

Artificial Sub-60 Millivolts/Decade Switching in a Metal-Insulator-Metal-Insulator-Semiconductor Transistor without a Ferroelectric Component.

Negative capacitance field-effect transistors (NC-FETs) have attracted wide interest as promising candidates for steep-slope devices, and sub-60 millivolts/decade (mV/decade) switching has been demonstrated in NC-FETs with various device structures and material systems. However, the detailed mechanisms of the observed steep-slope switching in some of these experiments are under intense debate. Here we show that sub-60 mV/decade switching can be observed in a WS transistor with a metal-insulator-metal-insulator-semiconductor (MIMIS) structure without any ferroelectric component.

Hardware implementation of Bayesian network building blocks with stochastic spintronic devices.

Bayesian networks are powerful statistical models to understand causal relationships in real-world probabilistic problems such as diagnosis, forecasting, computer vision, etc. For systems that involve complex causal dependencies among many variables, the complexity of the associated Bayesian networks become computationally intractable. As a result, direct hardware implementation of these networks is one promising approach to reducing power consumption and execution time.

Demonstration of a pseudo-magnetization based simultaneous write and read operation in a CoFeB/Pb(MgNb)TiO heterostructure.

Taking advantage of the magnetoelectric and its inverse effect, this article demonstrates strain-mediated magnetoelectric write and read operations simultaneously in CoFeB/Pb(MgNb)TiO heterostructures based on a pseudo-magnetization µ ≡ m- m. By applying an external DC-voltage across a (011)-cut PMN-PT substrate, the ferroelectric polarization is re-oriented, which results in an anisotropic in-plane strain that transfers to the CoFeB thin film and changes its magnetic anisotropy H. The change in H in-turn results in a 90° rotation of the magnetic easy axis for sufficiently high voltages.

Efficient Spin-Orbit Torque Switching of the Semiconducting Van Der Waals Ferromagnet Cr Ge Te.

Being able to electrically manipulate the magnetic properties in recently discovered van der Waals ferromagnets is essential for their integration in future spintronics devices. Here, the magnetization of a semiconducting 2D ferromagnet, i.e.

MoS for Enhanced Electrical Performance of Ultrathin Copper Films.

Copper nanowires are widely used as on-chip interconnects due to their superior conductivity. However, with aggressive Cu interconnect scaling, surface scattering of electrons drastically increases the electrical resistivity. In this work, we have studied the electrical performance of Cu thin films deposited on different materials.

Complementary Black Phosphorus Tunneling Field-Effect Transistors.

Band-to-band tunneling field-effect transistors (TFETs) have emerged as promising candidates for low-power integration circuits beyond conventional metal-oxide-semiconductor field-effect transistors (MOSFETs) and have been demonstrated to overcome the thermionic limit, which results intrinsically in sub-threshold swings of at least 60 mV/dec at room temperature. Here, we demonstrate complementary TFETs based on few-layer black phosphorus, in which multiple top gates create electrostatic doping in the source and drain regions. By electrically tuning the doping types and levels in the source and drain regions, the device can be reconfigured to allow for TFET or MOSFET operation and can be tuned to be n-type or p-type.

Electric-field induced structural transition in vertical MoTe- and MoWTe-based resistive memories.

Transition metal dichalcogenides have attracted attention as potential building blocks for various electronic applications due to their atomically thin nature and polymorphism. Here, we report an electric-field-induced structural transition from a 2H semiconducting to a distorted transient structure (2H) and orthorhombic T conducting phase in vertical 2H-MoTe- and MoWTe-based resistive random access memory (RRAM) devices. RRAM programming voltages are tunable by the transition metal dichalcogenide thickness and show a distinctive trend of requiring lower electric fields for MoWTe alloys versus MoTe compounds.

Spin-torque devices with hard axis initialization as Stochastic Binary Neurons.

Employing the probabilistic nature of unstable nano-magnet switching has recently emerged as a path towards unconventional computational systems such as neuromorphic or Bayesian networks. In this letter, we demonstrate proof-of-concept stochastic binary operation using hard axis initialization of nano-magnets and control of their output state probability (activation function) by means of input currents. Our method provides a natural path towards addition of weighted inputs from various sources, mimicking the integration function of neurons.

Characterization of Single Defects in Ultrascaled MoS Field-Effect Transistors.

MoS has received a lot of attention lately as a semiconducting channel material for electronic devices, in part due to its large band gap as compared to that of other 2D materials. Yet, the performance and reliability of these devices are still severely limited by defects which act as traps for charge carriers, causing severely reduced mobilities, hysteresis, and long-term drift. Despite their importance, these defects are only poorly understood.

Vertical charge transport through transition metal dichalcogenides - a quantitative analysis.

Based on the careful design of two-terminal devices from multi-layer transition metal dichalcogenides (TMDs) such as MoS and WSe, truly vertical transport has been experimentally evaluated and theoretically analyzed. By exploring, the electric field and temperature dependence of in total 28 TMD devices of various thicknesses, a model that describes vertical transport as Fowler Nordheim mediated at high electric fields and thermal injection dominated at low fields has been developed. Our approach is similar to the description chosen to capture gate leakage current levels through amorphous materials such as SiO.

Understanding contact gating in Schottky barrier transistors from 2D channels.

In this article, a novel two-path model is proposed to quantitatively explain sub-threshold characteristics of back-gated Schottky barrier FETs (SB-FETs) from 2D channel materials. The model integrates the "conventional" model for SB-FETs with the phenomenon of contact gating - an effect that significantly affects the carrier injection from the source electrode in back-gated field effect transistors. The two-path model is validated by a careful comparison with experimental characteristics obtained from a large number of back-gated WSe devices with various channel thicknesses.

Vertical versus Lateral Two-Dimensional Heterostructures: On the Topic of Atomically Abrupt p/n-Junctions.

The key appeal of two-dimensional (2D) materials such as graphene, transition metal dichalcogenides (TMDs), or phosphorene for electronic applications certainly lies in their atomically thin nature that offers opportunities for devices beyond conventional transistors. It is also this property that makes them naturally suited for a type of integration that is not possible with any three-dimensional (3D) material, that is, forming heterostructures by stacking dissimilar 2D materials together. Recently, a number of research groups have reported on the formation of atomically sharp p/n-junctions in various 2D heterostructures that show strong diode-type rectification.

Bandgap Extraction and Device Analysis of Ionic Liquid Gated WSe Schottky Barrier Transistors.

Through the careful study of ionic liquid gated WSe Schottky barrier field-effect transistors as a function of flake thickness-referred to in the following as body thickness, t-critical insights into the electrical properties of WSe are gained. One finding is that the inverse subthreshold slope shows a clear dependence on body thickness, i.e.

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

In the present paper, we show tungsten diselenide (WSe) 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 WSe 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.

Covalent Nitrogen Doping and Compressive Strain in MoS2 by Remote N2 Plasma Exposure.

Controllable doping of two-dimensional materials is highly desired for ideal device performance in both hetero- and p-n homojunctions. Herein, we propose an effective strategy for doping of MoS2 with nitrogen through a remote N2 plasma surface treatment. By monitoring the surface chemistry of MoS2 upon N2 plasma exposure using in situ X-ray photoelectron spectroscopy, we identified the presence of covalently bonded nitrogen in MoS2, where substitution of the chalcogen sulfur by nitrogen is determined as the doping mechanism.