The Schottky barrier transistor in emerging electronic devices

Contact Resistance Optimization in MoS2 Field-Effect Transistors through Reverse Sputtering-Induced Structural Modifications

Two-dimensional material (2DM)-based field-effect transistors (FETs), such as molybdenum disulfide (MoS2)-FETs, have gained significant attention for their potential for ultrashort channels, thereby extending Moore's law. However, MoS2-FETs are prone to the formation of Schottky barriers at the metal-MoS2 interface, resulting in high contact resistance (Rc) and, consequently, reduced transistor currents in the ON-state. Our study explores the modification of MoS2 to induce the formation of conductive 1T-MoS2 at the metal-MoS2 interface via reverse sputtering. MoS2-FETs exposed to optimized reverse sputtering conditions in the contact area show Rc values reduced to less than 50% of their untreated counterparts. This reduction translates into improvements in other electrical characteristics, such as higher ON-state currents. Since reverse sputtering is a standard semiconductor process that enhances the electrical performance of MoS2-FETs, it has great potential for broader application scenarios in 2DM-based microelectronic devices and circuits.

Thermionic injection analysis in germanium nanowire Schottky junction FETs by means of 1D and 3D extraction methods

Schottky barrier field-effect transistors (SBFETs) are a promising family of devices suitable for realizing "Beyond CMOS" paradigms. As the SBFET device operation is strongly dependent on the metal-semiconductor junction properties, it is important to extract and understand the activation energy to inject charge carriers into the semiconductor channel. In this regard, the three-dimensional (3D) thermionic emission (TE) and the one-dimensional (1D) Landauer-Büttiker (LB) theory are among the most sophisticated methods. Here, both methods are used to analyze the charge carrier injection capabilities of Al-Ge-Al nanowire (NW) heterostructure SBFETs. While the 3D TE model underestimates the activation energy E a in strong accumulation, at the intrinsic off-point, where merely TE contributes to charge carrier transport, both models provide reasonable values close to the theoretically expected Schottky barrier height. Analyzing the underlying mathematical models of 3D TE and 1D LB reveals a quadratic and linear increase in TE depending on temperature, respectively. Moreover, until now effects on the E a originating from the 1D nature of the proposed device were rarely investigated in NW transistors. This comparison contributes to a better understanding and the advancement of SBFET devices and circuit technologies.

Mechanical-Stimuli-Driven Pseudo-Conductive Channels Along Dielectric Heterojunction Interfaces for Mechanoelectric Energy Conversion and Transmission

Mechanoelectric energy conversion holds promise for energy conversion and transmission devices, yet conventional configurations rely on large-area conductive materials in active regions, limiting architectural design for cutting-edge devices. Here, a rational strategy is reported to create mechanical stimuli-driven pseudo-conductive (MSPC) channels entirely from dielectric materials, eliminating the need for electrodes in active regions. An in-depth investigation of MSPC channel formation mechanism at dielectric interfaces is conducted, employing energy band analyses. Following the mechanical stimuli-driven charging process, MSPC device effectively transmits electrical signals over 42 mm, achieving remarkable 512% enhancement compared to its pristine state. Control devices with non-continuous dielectric configurations highlight the impact of heterojunction interfaces on MSPC channels. A resistor-capacitor charging test reveals up to 49% reduction in voltage change rate, indicating a substantial decrease in electrical impedance along the MSPC channel. Furthermore, MSPC devices demonstrate information transmission capabilities, such as sequences of bits or letters, utilizing solely dielectric configurations. This study paves the way to reduce conductive materials of wearable electronics, biomedical implants, and IoT technologies, overcoming significant challenges such as potential electrical shortages, design inflexibility, limited manufacturing scalability, and maintenance issues.

Understanding the Effect of Electron Irradiation on WS2 Nanotube Devices to Improve Prototyping Routines

To satisfy the needs of the current technological world that demands high performance and efficiency, a deep understanding of the whole fabrication process of electronic devices based on low-dimensional materials is necessary for rapid prototyping of devices. The fabrication processes of such nanoscale devices often include exposure to an electron beam. A field effect transistor (FET) is a core device in current computation technology, and FET configuration is also commonly used for extraction of electronic properties of low-dimensional materials. In this experimental study, we analyze the effect of electron beam exposure on electrical properties of individual WS2 nanotubes in the FET configuration by in-operando transport measurements inside a scanning electron microscope. Upon exposure to the electron beam, we observed a significant change in the resistance of individual substrate-supported nanotubes (by a factor of 2 to 14) that was generally irreversible. The resistance of each nanotube did not return to its original state even after keeping it under ambient conditions for hours to days. Furthermore, we employed Kelvin probe force microscopy to monitor surface potential and identified that substrate charging is the primary cause of changes in nanotubes' resistance. Hence, extra care should be taken when analyzing nanostructures in contact with insulating oxides that are subject to electron exposure during or after fabrication.

Device simulation study of multilayer MoS2Schottky barrier field-effect transistors

Molybdenum disulfide (MoS2) is a representative two-dimensional layered transition-metal dichalcogenide semiconductor. Layer-number-dependent electronic properties are attractive in the development of nanomaterial-based electronics for a wide range of applications including sensors, switches, and amplifiers. MoS2field-effect transistors (FETs) have been studied as promising future nanoelectronic devices with desirable features of atomic-level thickness and high electrical properties. When a naturallyn-doped MoS2is contacted with metals, a strong Fermi-level pinning effect adjusts a Schottky barrier and influences its electronic characteristics significantly. In this study, we investigate multilayer MoS2Schottky barrier FETs (SBFETs), emphasizing the metal-contact impact on device performance via computational device modeling. We find thatp-type MoS2SBFETs may be built with appropriate metals and gate voltage control. Furthermore, we propose ambipolar multilayer MoS2SBFETs with asymmetric metal electrodes, which exhibit gate-voltage dependent ambipolar transport behavior through optimizing metal contacts in MoS2device. Introducing a dual-split gate geometry, the MoS2SBFETs can further operate in four distinct configurations:p - p,n - n,p - n, andn - p. Electrical characteristics are calculated, and improved performance of a high rectification ratio can be feasible as an attractive feature for efficient electrical and photonic devices.

Understanding the Electronic Transport of Al-Si and Al-Ge Nanojunctions by Exploiting Temperature-Dependent Bias Spectroscopy

Understanding the electronic transport of metal-semiconductor heterojunctions is of utmost importance for a wide range of emerging nanoelectronic devices like adaptive transistors, biosensors, and quantum devices. Here, we provide a comparison and in-depth discussion of the investigated Schottky heterojunction devices based on Si and Ge nanowires contacted with pure single-crystal Al. Key for the fabrication of these devices is the selective solid-state metal-semiconductor exchange of Si and Ge nanowires into Al, delivering void-free, single-crystal Al contacts with flat Schottky junctions, distinct from the bulk counterparts. Thereof, a systematic comparison of the temperature-dependent charge carrier injection and transport in Si and Ge by means of current-bias spectroscopy is visualized by 2D colormaps. Thus, it reveals important insights into the operation mechanisms and regimes that cannot be exploited by conventional single-sweep output and transfer characteristics. Importantly, it was found that the Al-Si system shows symmetric effective Schottky barrier (SB) heights for holes and electrons, whereas the Al-Ge system reveals a highly transparent contact for holes due to Fermi level pinning close to the valence band with charge carrier injection saturation due to a thinned effective SB. Moreover, thermionic field emission limits the overall electron conduction, indicating a distinct SB for electrons.