High On-off Ratio Research Articles

Self-driven Te0.65Se0.35/GaAs SWIR photodiode with spectral response to 1.55 μm for broadband imaging and optical communication

Te-based photodetectors with the merits of low cost and CMOS-compatible fabrication process have been considered promising for broadband imaging applications. Nevertheless, the spectral response of reported devices under self-powered mode is generally limited to near-infrared wavelength below 1100 nm (corresponding to the bandgap of Si). This could be ascribed to the high room-temperature carrier density in Te and the ease of forming Type-I heterojunctions between Te and other semiconductors, which impede the effective generation and separation of photocarriers. This study reports the bandgap engineering of Te through Te-Se alloying and the fabrication of Te0.65Se0.35/Al2O3/GaAs photodiode with an extended response spectrum through ultraviolet to the short-wave infrared (SWIR) band of 1550 nm at zero bias. The effects of interface passivation on the photosensing properties were also investigated. The optimized heterojunction exhibits a pronounced photovoltaic response to 1342 nm (1550 nm) infrared light with an open-circuit voltage of ∼0.12 V (0.07 V). Particularly, the dark current density reaches a record low level of 0.1 nA/cm2 at 0 V bias, leading to a high on-off current ratio of 4.5×104 and detectivity of 1.1×107 Jones at room temperature for 1342 nm light. Self-powered UV-Vis-SWIR broadband imaging and optical communication are realized by leveraging the favorable device performance. Our work provides a frame of reference for exploring more Te1-xSex-based photodetectors. Meanwhile, it may be combined with well-developed semiconductor processing technologies for optoelectronics integration.

Sliding Ferroelectricity Induced Ultrafast Switchable Photovoltaic Response in ε-InSe Layers.

2D sliding ferroelectric semiconductors have greatly expanded the ferroelectrics family with the flexibility of bandgap and material properties, which hold great promise for ultrathin device applications that combine ferroelectrics with optoelectronics. Besides the induced different resistance states for non-volatile memories, the switchable ferroelectric polarizations can also modulate the photogenerated carriers for potentially ultrafast optoelectronic devices. Here, it is demonstrated that the room temperature sliding ferroelectricity can be used for ultrafast switchable photovoltaic response in ε-InSe layers. By first-principles calculations and experimental characterizations, it is revealed that the ferroelectricity with out-of-plane (OOP) polarization only exists in even layer ε-InSe. The ferroelectricity is also demonstrated in ε-InSe-based vertical devices, which exhibit high on-off ratios (≈104) and non-volatile storage capabilities. Moreover, the OOP ferroelectricity enables an ultrafast (≈3ps) bulk photovoltaic response in the near-infrared band, rendering it a promising material for self-powered reconfigurable and ultrafast photodetector. This work reveals the essential role of ferroelectric polarization on the photogenerated carrier dynamics and paves the way for hybrid multifunctional ferroelectric and optoelectronic devices.

Large-scale sub-5-nm vertical transistors by van der Waals integration

Vertical field effect transistor (VFET), in which the semiconductor is sandwiched between source/drain electrodes and the channel length is simply determined by the semiconductor thickness, has demonstrated promising potential for short channel devices. However, despite extensive efforts over the past decade, scalable methods to fabricate ultra-short channel VFETs remain challenging. Here, we demonstrate a layer-by-layer transfer process of large-scale indium gallium zinc oxide (IGZO) semiconductor arrays and metal electrodes, and realize large-scale VFETs with ultra-short channel length and high device performance. Within this process, the oxide semiconductor could be pre-deposited on a sacrificial wafer, and then physically released and sandwiched between metals, maintaining the intrinsic properties of ultra-scaled vertical channel. Based on this lamination process, we realize 2 inch-scale VFETs with channel length down to 4 nm, on-current over 800 A/cm2, and highest on-off ratio up to 2 × 105, which is over two orders of magnitude higher compared to control samples without laminating process. Our study not only represents the optimization of VFETs performance and scalability at the same time, but also offers a method of transfer large-scale oxide arrays, providing interesting implication for ultra-thin vertical devices.

Ballistic Frenkel-exciton gate with a high on-off ratio

Ballistic Frenkel-exciton gate with a high on-off ratio

Unlocking High-Performance, Ultra-Low Power van der Waals Photo-Transistors: Toward Back-End-of-Line in-Sensor Machine Vision Applications.

Recent reports on machine learning and machine vision (MV) devices have demonstrated the potential of two-dimensional (2D) materials and devices. Yet, scalable 2D devices are being challenged by contact resistance and Fermi level pinning (FLP), power consumption, and low-cost CMOS compatible lithography processes. To enable CMOS + 2D, it is essential to find a proper lithography strategy that can fulfill these requirements. Here, we explored a modified van der Waals (vdW) deposition lithography and demonstrated a relatively new class of van der Waals field effect transistors (vdW-FETs) based on 2D materials. This lithography strategy enabled us to unlock high-performance devices evident by high current on-off ratio (Ion/Ioff), high turn-on current density (Ion), and weak FLP. We utilized this approach to demonstrate a gate-tunable near-ideal diode using a MoS2/WSe2 heterojunction with an ideality factor of ∼1.65 and current rectification of 102. We finally demonstrated a highly sensitive, scalable, and ultralow power phototransistor using a MoS2/WSe2 vdW-FET for back-end-of-line integration. Our phototransistor exhibited the highest gate-tunable photoresponsivity achieved to date for white light detection with ultralow power dissipation, enabling ultrasensitive optoelectronic applications such as in-sensor MV. Our approach showed the great potential of modified vdW deposition lithography for back-end-of-line CMOS + 2D applications.

High growth rate metal organic chemical vapor deposition grown Ga2O3 (010) Schottky diodes

We report on the growth of Si-doped homoepitaxial β-Ga2O3 thin films on (010) Ga2O3 substrates via metal-organic chemical vapor deposition (MOCVD) utilizing triethylgallium (TEGa) and trimethylgallium (TMGa) precursors. The epitaxial growth achieved an impressive 9.5 μm thickness at 3 μm/h using TMGa, a significant advance in material growth for electronic device fabrication. This paper systematically studies the Schottky barrier diodes fabricated on the three MOCVD-grown films, each exhibiting variations in the epilayer thickness, doping levels, and growth rates. The diode from the 2 μm thick Ga2O3 epilayer with TEGa precursor demonstrates promising forward current densities, the lowest specific on-resistance, and the lowest ideality factor, endorsing TEGa’s potential for MOCVD growth. Conversely, the diode from the 9.5 μm thick Ga2O3 layer with TMGa precursor exhibits excellent characteristics in terms of lowest leakage current, highest on-off ratio, and highest reverse breakdown voltage of −510 V without any electric field management, emphasizing TMGa’s suitability for achieving high growth rates in Ga2O3 epilayers for vertical power electronic devices.

Analysis of Negative Capacitance Source Pocket Double-Gate TFET with Steep Subthreshold and High ON–OFF Ratio

Analysis of Negative Capacitance Source Pocket Double-Gate TFET with Steep Subthreshold and High ON–OFF Ratio

Ferroelectric capacitors and field-effect transistors as in-memory computing elements for machine learning workloads

This study discusses the feasibility of Ferroelectric Capacitors (FeCaps) and Ferroelectric Field-Effect Transistors (FeFETs) as In-Memory Computing (IMC) elements to accelerate machine learning (ML) workloads. We conducted an exploration of device fabrication and proposed system-algorithm co-design to boost performance. A novel FeCap device, incorporating an interfacial layer (IL) and Hf0.5Zr0.5O2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {Hf}_{0.5}\ ext {Zr}_{0.5}\ ext {O}_2$$\\end{document} (HZO), ensures a reduction in operating voltage and enhances HZO scaling while being compatible with CMOS circuits. The IL also enriches ferroelectricity and retention properties. When integrated into crossbar arrays, FeCaps and FeFETs demonstrate their effectiveness as IMC components, eliminating sneak paths and enabling selector-less operation, leading to notable improvements in energy efficiency and area utilization. However, it is worth noting that limited capacitance ratios in FeCaps introduced errors in multiply-and-accumulate (MAC) computations. The proposed co-design approach helps in mitigating these errors and achieves high accuracy in classifying the CIFAR-10 dataset, elevating it from a baseline of 10% to 81.7%. FeFETs in crossbars, with a higher on-off ratio, outperform FeCaps, and our proposed charge-based sensing scheme achieved at least an order of magnitude reduction in power consumption, compared to prevalent current-based methods.

High-Density, Nonvolatile, Flexible Multilevel Organic Memristor Using Multilayered Polymer Semiconductors.

Nonvolatile organic memristors have emerged as promising candidates for next-generation electronics, emphasizing the need for vertical device fabrication to attain a high density. Herein, we present a comprehensive investigation of high-performance organic memristors, fabricated in crossbar architecture with PTB7/Al-AlOx-nanocluster/PTB7 embedded between Al electrodes. PTB7 films were fabricated using the Unidirectional Floating Film Transfer Method, enabling independent uniform film fabrication in the Layer-by-Layer (LbL) configuration without disturbing underlying films. We examined the charge transport mechanism of our memristors using the Hubbard model highlighting the role of Al-AlOx-nanoclusters in switching-on the devices, due to the accumulation of bipolarons in the semiconducting layer. By varying the number of LbL films in the device architecture, the resistance of resistive states was systematically altered, enabling the fabrication of novel multilevel memristors. These multilevel devices exhibited excellent performance metrics, including enhanced memory density, high on-off ratio (>108), remarkable memory retention (>105 s), high endurance (87 on-off cycles), and rapid switching (∼100 ns). Furthermore, flexible memristors were fabricated, demonstrating consistent performance even under bending conditions, with a radius of 2.78 mm for >104 bending cycles. This study not only demonstrates the fundamental understanding of charge transport in organic memristors but also introduces novel device architectures with significant implications for high-density flexible applications.

A Green High-k Dielectric from Modified Carboxymethyl Cellulose-Based with Dextrin.

Many crucial components inside electronic devices are made from non-renewable, non-biodegradable, and potentially toxic materials, leading to environmental damage. Finding alternative green dielectric materials is mandatory to align with global sustainable goals. Carboxymethyl cellulose (CMC) is a bio-polymer derived from cellulose and has outstanding properties. Herein, citric acid, dextrin, and CMC based hydrogels are prepared, which are biocompatible and biodegradable and exhibit rubber-like mechanical properties, with Young modulus values of 0.89 MPa. Hence, thin film CMC-based hydrogel is explored as a suitable green high-k dielectric candidate for operation at low voltages, demonstrating a high dielectric constant of up to 78. These fabricated transistors reveal stable high capacitance (2090 nF cm-2) for ≈±3V operation. Using a polyelectrolyte-type approach and poly-(2-vinyl anthracene) (PVAn) surface modification, this study demonstrates a thin dielectric layer (d ≈30 nm) with a small voltage threshold (Vth ≈-0.8 V), moderate transconductance (gm ≈65 nS), and high ON-OFF ratio (≈105). Furthermore, the dielectric layer exhibits stable performance under bias stress of ± 3.5 V and 100 cycles of switching tests. The modified CMC-based hydrogel demonstrates desirable performance as a green dielectric for low-voltage operation, further highlighting its biocompatibility.

Controllable single-photon transport mediated by a time-modulated Jaynes–Cummings model

Controllable single-photon scattering in a one-dimensional waveguide coupled to a Jaynes–Cummings structure containing a time-modulated two-level atom interacting with a single-mode cavity is investigated. The photon transmission and reflection amplitudes are calculated by using an effective Floquet Hamiltonian in real space. The results show that the coupling between the atom and the cavity mode can dynamically be tuned via periodically modulating the atomic transition frequency. As a consequence, the scattering behaviors of the waveguide photons can be actively manipulated, and a controllable single-photon switch with high on-off ratio could be realized. More interestingly, the switch works well within a wide frequency region, i.e., the transmission of both resonant and off-resonant waveguide photons can be effectively switched on or off with appropriate system parameters. Furthermore, the proposed dynamically tunable switching scheme is robust against atomic dissipation associated with the help of atom-cavity coupling mismatch. Such single-photon device can be used as an elementary unit for various quantum information processing.

Dynamics of interfacial charge transfer between CsPbBr3 perovskite nanocrystals and molecular acceptors for photodetection application

Perovskite nanocrystals (NCs) recently emerged as a suitable candidate for optoelectronic applications because of its simplistic synthesis approach and superior optical properties. For better device performance, the effective absorption of incident photons and the understanding of charge transfer (CT) process are the basic requirements. Herein, we investigate the interfacial charge transfer dynamics of CsPbBr3 NCs in the presence of different molecular acceptors; 7,7,8,8-Tetracyanoquinodimethane (TCNQ) and 11,11,12,12 tetracyanonaphtho-2,6-quinodimethane (TCNAQ). The vivid change in CT dynamics at the interfaces of NCs and two different molecular acceptors (TCNQ and TCNAQ) has been observed. The results demonstrate that the ground state complex formation in the presence of TCNQ acts as additional driving force to accelerate the charge transfer between the NCs and molecular acceptor. Moreover, this donor (NCs)-acceptor (TCNQ, TCNAQ) system results in the higher absorption of incident photons. Finally, the photo detector based on CsPbBr3-TCNQ system was fabricated for the first time. The device exhibited a high on–off ratio (104). Furthermore, the CsPbBr3-TCNQ photodetector shows a fast photoresponse times of 180 ms/110 ms (rise/decay time) with a specific detectivity (D*) of 5.2 × 1011 Jones. The simple synthesis and outstanding photodetection abilities of this perovskite NCs-molecular acceptor system make them potential candidates for optoelectronic applications.

Monitoring of UV-A radiation by TiO2/CdS nanohybrid along with the high on-off ratio

Exposure to UV-A light can have detrimental effects on human health, leading to skin damage and an increased risk of skin cancer. In this study, we employed a hydrothermal-assisted method to cultivate TiO2-decorated CdS nanorods for use in UV photodetectors. Our research culminated in the fabrication of an exceptionally responsive and rapid photodetector based on the TiO2/CdS nanohybrid. X-ray diffraction analysis revealed the hexagonal phase of CdS nanorods, predominantly oriented along the (002) plane, and the presence of the anatase phase of TiO2. Scanning electron microscopy (SEM) measurements confirmed the nanorod structure of TiO2/CdS. Optical properties of the TiO2/CdS nanohybrid were investigated through UV–visible absorbance analysis. Additionally, X-ray photoelectron spectroscopy (XPS) provided insights into the surface composition of the prepared nanohybrid, with peaks corresponding to Cd 3d3/2 and Cd 3d5/2 at binding energies of 411.47 eV and 404.73 eV, respectively, and confirming the presence of titanium through peaks of Ti 2p3/2 and 2p1/2 at binding energies of 458.31 eV and 463.8 eV, respectively. Raman analysis indicated the presence of the anatase phase of TiO2 in the composite. Our device exhibited an impressive detectivity of 9.9 × 1012 Jones, an EQE (external quantum efficiency) of 971.36%, and a high photoresponsivity of 2.86 A/W. These results suggest that TiO2/CdS nanohybrids, prepared using a cost-effective and straightforward method, hold promise for UV photodetection applications.

2D MXene electrochemical transistors.

The solid-state field-effect transistor, FET, and its theories were paramount in the discovery and studies of graphene. In the past two decades another transistor based on conducting polymers, called organic electrochemical transistor (ECT), has been developed and largely studied. The main difference between organic ECTs and FETs is the mode and extent of channel doping; while in FETs the channel only has surface doping through dipoles, the mixed ionic-electronic conductivity of the channel material in organic ECTs enables bulk electrochemical doping. As a result, organic ECTs maximize conductance modulation at the expense of speed. To date ECTs have been based on conducting polymers, but here we show that MXenes, a class of 2D materials beyond graphene, enable the realization of electrochemical transistors (ECTs). We show that the formulas for organic ECTs can be applied to these 2D ECTs and used to extract parameters like mobility. These MXene ECTs have high transconductance values but low on-off ratios. We further show that conductance switching data measured using ECT, in combination with other in situ-ex situ electrochemical measurements, is a powerful tool for correlating the change in conductance to that of the redox state, to our knowledge, this is the first report of this important correlation for MXene films. 2D ECTs can draw great inspiration and theoretical tools from the field of organic ECTs and have the potential to considerably extend the capabilities of transistors beyond those of conducting polymer ECTs, with added properties such as extreme heat resistance, tolerance for solvents, and higher conductivity for both electrons and ions than conducting polymers.

Low voltage-driven, high-performance TiO2 thin film transistors with MHz switching speed.

High-speed circuits based on thin film transistors (TFTs) show promising potential applications in biomedical imaging and human-machine interactions. One of the critical requirements for high-speed electronic devices lies in high-frequency switching or amplification at low voltages, typically driven by batteries (∼3.0 V). To date, however, most electrical performances of metal oxide TFTs are measured under direct current (DC) conditions, and their dynamic switching behaviour is scarcely explored and studied systematically. Here in this work, we present low voltage-driven, high-performance TiO2 thin film transistors, which can be operated at a switching speed of MHz. Our proposed TiO2 TFTs demonstrated a high on-off ratio of 107, together with a subthreshold swing (SS) of ∼150 mV Dec-1 averaged over four orders of magnitude, which can be further reduced below 100 mV Dec-1 when the temperature cools to 77 K. Additionally, the TiO2 TFTs exhibit excellent gate-pulse switching at various frequencies ranging from 1.0 Hz to 1.0 MHz. We also explored the potential application of the TiO2 TFTs as logic gates by constructing a resistive-loaded inverter, which shows stable operation at 10 kHz frequency and various temperatures. Thus, our results show the great potential of TiO2 TFTs as a new platform for high-speed electronic applications.

Inkjet printing high mobility indium-zinc-tin oxide thin film transistor

Metal oxide thin film transistor has been widely used in flat panel display industry because of its low leakage current, high mobility and large area uniformity. Besides, with the development of printed display technology, inkjet printing process can fabricate the customizable patterns on diverse substrates with no need of vacuum or lithography to be used, thus significantly reducing cost and receiving more and more attention. In this paper, we use inkjet printing technology to prepare a bottom gate bottom contact thin film transistor (TFT) by using indium-zinc-tin-oxide (IZTO) semiconductor. The surface morphology of the printed IZTO film is modified by adjusting the solvent composition and solute concentration of the printing precursor ink. The experimental result show that the use of binary solvents can effectively overcome the coffee ring shape caused by the accumulation of solute edge in the volatilization process of a single solvent, ultimately presenting a uniform and flat contour surface. Further increase in solute concentration is in favor of formation of convex surface topology. The reason for the formation of the flat surface of the oxide film is the balance between the inward Marangoni reflux of the solute and the outward capillary flow during volatilization. In addition, IZTO thin film transistor printed with binary solvents exhibits excellent electrical properties. The ratio of width/length = 50/30 exhibits a high on-off ratio of 1.21×10<sup>9</sup>, a high saturation field-effect mobility is 16.6 cm<sup>2</sup>/(V·s), a low threshold voltage is 0.84 V, and subthreshold swing is 0.24 V/dec. The uniform and flat active layer thin film pattern can form good contact with the source leakage electrode, and the contact resistances of TFT devices with different width-to-length ratios are less than 1000 Ω, which can reach the basic conditions of high mobility thin film transistors prepared by inkjet printing. Therefore, using solvent mixture provides a universal and simple way to print oxide films with required surface topology, and present a visible path for inkjet printing of high-mobility thin film transistors.

(Invited) Vertically Stacked Graphene Junction Diodes

Graphene is expected to be nanomaterial of the post-silicon era because of its numerous advantageous properties. The single crystal graphene thermally grown on SiC substrate is considered the most promising platform for future electric devices. Large area epitaxial graphene on SiC substrate has been successfully fabricated using high-temperature rapid thermal annealing [1]. In this study, we present vertically stacked graphene junction diodes fabricated using direct bonding technique [2–4]. Figure 1(a) shows the schematic of a stacked graphene junction diode. Two graphene layers on SiC are directly bonded to each other. Gold–coated contact pins are attached to the graphene surface to establish ohmic contact. The graphene samples and contact probes are fixed by acrylic molds. Strong nonlinear current–voltage (I-V) characteristics are observed for this simple device configuration, as shown in Fig. 1(b). In the low bias voltage (Vb) region, the resistance of the graphene diode is approximately 20 GΩ. The current abruptly increases when the bias voltage is increased to approximately 30 V. The two-terminal resistance at a high bias voltage (100 V) is approximately 21 kΩ. The vertically stacked graphene junction exhibits bidirectional thyristor-type characteristics with a high on-off ratio of approximately 106. The Fowler–Nordheim (F-N) tunneling phenomenon is observed in the sub-threshold region. The gap distance estimated from the F-N plot is approximately 6 nm, which can be attributed to the large off resistance. The Coulomb force generated by applying the bias voltage causes the two graphene layers to attract each other, resulting in an electrically conductive state. The junction voltage (Vj) of the device was measured using a four-terminal configuration. As shown in Fig. 1(c), negative resistance is observed in the low-resistance region. The effective internal resistance of the junction diode is reduced to approximately 450 Ω. The off resistance of the diodes is considerably modified by the initial distance between the graphene layers. However, the I-Vj characteristics in the negative resistance region are identical for each device. This result suggests that the cause of the negative resistance phenomena is closely related to the band structure of graphene. A vertically stacked graphene junction diode with a high on-off ratio was demonstrated. The main component of the diode comprised a pair of single-crystal graphene layers fabricated through direct bonding. The negative resistance of the graphene diode presents new possibilities for the application of functional devices, such as terahertz emitters.[1] T. Aritsuki, et al., Jpn. J. Appl. Phys. 55 (2016) 06GF03.[2] J. Du, eta al., Jpn. J. Appl. Phys. 58 (2019) SDDE01.[3] N. Murakami, et al., Jpn. J. Appl. Phys. 60 (2021) SCCD01.[4] M. Ohi, et al., Jpn. J. Appl. Phys. 62 (2023) to be published. Figure 1

Highly Reliable Van Der Waals Memory Boosted by a Single 2D Charge Trap Medium.

Charge trap materials that can store carriers efficiently and controllably are desired for memory applications. 2D materials are promising for highly compacted and reliable memory mainly due to their ease of constructing atomically uniform interfaces, however, remain unexplored as being charge trap media. Here it is discovered that 2D semiconducting PbI2 is an excellent charge trap material for nonvolatile memory and artificial synapses. It is simple to construct PbI2 -based charge trap devices since no complicated synthesis or additional defect manufacturing are required. As a demonstration, MoS2 /PbI2 device exhibits a large memory window of 120V, fast write speed of 5 µs, high on-off ratio around 106 , multilevel memory of over 8 distinct states, high reliability with endurance up to 104 cycles and retention over 1.2 × 104 s. It is envisioned that PbI2 with ionic activity caused by the natively formed iodine vacancies is unique to combine with unlimited 2D materials for versatile van der Waals devices with high-integration and multifunctionality.

High performance junctionless FDSOI SiGe channel p-FinFET with high ION/IOFF ratio and excellent SS

This paper presents a novel FDSOI FinFETs with SiGe channel/Si cap layer (35 nm/5 nm) formed on SOI wafers with 20 nm Si body. Electrical characterization result shows that JL FDSOI FinFETs with SiGe channel exhibited low subthreshold slope (SS) of 86 mV/decade and record high ON-OFF current ratio (ION/IOFF = 2 × 106) at VD = -0.5V, respectively. Device performance improvement was mainly attributed to high-epitaxial quality compressive strained SiGe channel and novel device structure. The strain in the channel of the transistors was estimated locally in TEM using Nano beam diffraction (NBD) technique. The FDSOI FinFET with SiGe channel, lays the foundation for the further development of high speed, high density, low cost, and 3D monolithic integration circuits.

The fabrication of self-powered P-I-N perovskite photodetectors with high on-off ratio using cuprous thiocyanate as hole transport layer

The fabrication of self-powered P-I-N perovskite photodetectors with high on-off ratio using cuprous thiocyanate as hole transport layer