Hybrid Field-effect Transistor Research Articles

Hybrid MoSe2/P3HT Transistor for Real-Time Ammonia Sensing in Biofluids.

Organic and inorganic hybrid field-effect transistors (FETs), utilizing layered molybdenum diselenide (MoSe2) and an organic semiconductor poly(3-hexylthiophene) (P3HT), are presented for biosensing applications. A new hybrid device structure that combines organic (P3HT) and inorganic (MoSe2) components is showcased for accurate and selective bioanalyte detection in human bodily fluids to overcome 2D-transition metal dichalcogenides (TMDs) nonspecific interactions. This hybrid structure utilizes organic and inorganic semiconductors' high surface-to-volume ratio, carrier transport, and conductivity for biosensing. Ammonia concentrations in saliva and plasma are closely linked to physiological and pathological conditions of the human body. A highly sensitive hybrid FET biosensor detects total ammonia (NH4+ and NH3) from 0.5 μM to 1 mM concentrations, with a detection limit of 0.65 μM in human bodily fluids. The sensor's ammonia specificity in artificial saliva against interfering species is showcased. Furthermore, the fabricated hybrid FET device exhibits a stable and repeatable response to ammonia in both saliva and plasma, achieving a remarkable response level of 2300 at a 1 mM concentration of ammonia, surpassing existing literature by 10-fold. This hybrid FET biosensing platform holds significant promise for developing a precise tool for the real-time monitoring of ammonia concentrations in human biological fluids, offering potential applications in point-of-care diagnostics.

Increased Mobility and Reduced Hysteresis of MoS2 Field-Effect Transistors via Direct Surface Precipitation of CsPbBr3-Nanoclusters for Charge Transfer Doping.

Transition-metal dichalcogenides (TMDs) and metal halide perovskites (MHPs) have been investigated for various applications, owing to their unique physical properties and excellent optoelectronic functionalities. TMD monolayers synthesized via chemical vapor deposition (CVD), which are advantageous for large-area synthesis, exhibit low mobility and prominent hysteresis in the electrical signals of field-effect transistors (FETs) because of their native defects. In this study, we demonstrate an increase in electrical mobility by ∼170 times and reduced hysteresis in the current-bias curves of MoS2 FETs hybridized with CsPbBr3 for charge transfer doping, which is implemented via solution-based CsPbBr3-nanocluster precipitation on CVD-grown MoS2 monolayer FETs. Electrons injected from CsPbBr3 into MoS2 induce heavy n-doping and heal point defects in the MoS2 channel layer, thus significantly increasing mobility and reducing hysteresis in the hybrid FETs. Our results provide a foundation for improving the reliability and performance of TMD-based FETs by hybridizing them with solution-based perovskites.

Strain Release in GaN Epitaxy on 4° Off-Axis 4H-SiC.

A hybrid field-effect transistor (HyFET), superior for power electronic applications, can be created by harnessing the merits of two representative wide-bandgap semiconductors, gallium nitride (GaN) and silicon carbide (SiC). Yet, the incompactness in the epitaxy techniques hinders the development of the HyFET-GaN is usually grown on on-axis foreign substrates including SiC, whereas SiC homoepitaxy prefers off-axis substrates. This work presents a GaN-based heterostructure epitaxially grown on a conventional 4° off-axis 4H-SiC substrate, which manifests its high quality and suitability for constructing GaN-based high-electron-mobility transistors, thereby suggesting a practical approach to realizing HyFETs. In the meanwhile, a distinct two-step biaxial strain-relaxation process is proposed and studied with comprehensive characterizations.

Memristive effects due to charge transfer in graphene gated through ferroelectric CuInP2S6

Ferroelectricity at the nanometre scale can drive the miniaturisation and wide application of ferroelectric devices for memory and sensing applications. The two-dimensional van der Waals (2D-vdWs) ferroelectrics CuInP2S6 (CIPS) has attracted much attention due to its robust ferroelectricity found in thin layers at room temperature. Also, unlike many 2D ferroelectrics, CIPS is a wide band gap semiconductor, well suited for use as a gate in field-effect transistors (FETs). Here, we report on a hybrid FET in which the graphene conducting channel is gated through a CIPS layer. We reveal hysteresis effects in the transfer characteristics of the FET, which are sensitive to the gate voltage, temperature and light illumination. We demonstrate charge transfer at the CIPS/graphene interface in the dark and under light illumination. In particular, light induces a photodoping effect in graphene that varies from n- to p-type with increasing temperature. These hybrid FETs open up opportunities for electrically and optically controlled memristive devices.

Field‐Assisted Sensitivity Amplification in a Noble Metal Nanoparticle Decorated WO3/GO Hybrid FET‐Based Multisensory Array for Selective Detection of Breath Acetone

AbstractSelective detection of acetone levels in exhaled human breath is important to diagnose complications of diabetes mellitus by the non‐invasive route. In the current study, we are reporting a hybrid graphene oxide (GO) field‐effect transistor (FET) based multisensory array for the selective detection of breath acetone by using a feature extraction and pattern recognition route. Backgated GO‐FET was functionalized with WO3 flower‐shaped nanostructures and noble metal (Au, Pd, Pt) nanoparticles to form hybrid FET sensors. By applying optimized gate voltages, the sensor response was enhanced several orders at room temperature. Therefore, an array of six sensors was tested in synthetic breath consisting of a complex mixture of multiple volatile organic compounds, various gases, 70% relative humidity and different levels of acetone. The sensors′ outcomes were then processed with phase space entire feature extraction method, and the different levels of acetone were differentiated in the synthetic breath by using Fisher discriminant analysis.

Impact of the channel length on molybdenum disulfide field effect transistors with hafnia-based high-k dielectric gate

Field effect transistors (FETs) using two-dimensional molybdenum disulfide (MoS2) as the channel material has been considered one of the most potential candidates for future complementary metal-oxide-semiconductor technology with low power consumption. However, the understanding of the correlation between the device performance and material properties, particularly for devices with scaling-down channel lengths, is still insufficient. We report in this paper back-gate FETs with chemical-vapor-deposition grown and transferred MoS2 and Zr doped HfO2 ((Hf,Zr)O2, HZO) high-k dielectric gates with channel lengths ranging from 10 to 30 µm with a step of 5 µm. It has been demonstrated that channels with the length to width ratio of 0.2 lead to the most superior performance of the FETs. The MoS2/HZO hybrid FETs show a stable threshold voltage of ∼1.5 V, current on/off ratio of >104, and field effect mobility in excess of 0.38 cm2 V−1 s−1. The impact of the channel lengths on FET performance is analyzed and discussed in depth. A hysteresis loop has been observed in the Ids − Vgs characteristics of the hybrid FETs, which has been further studied and attributed to the charge effect at the interfaces. The HZO films show a relatively weak ferroelectric orthorhombic phase and thus serve mainly as the high-k dielectric gate. Charge trapping in the HZO layer that might induce hysteresis has been discussed. Our results show that MoS2/HZO hybrid FETs possess great potential in future low power and high-speed integrated circuits, and future work will focus on further improvement of the transistor performances using ferroelectric HZO films and the study of devices with even shorter MoS2 channels.

Organic Field Effect Transistors: Noncovalent Functionalization and Passivation of Black Phosphorus with Optimized Perylene Diimides for Hybrid Field Effect Transistors (Adv. Mater. Interfaces 23/2020)

The noncovalent functionalization of two-dimensional black phosphorus (BP) with tailor made perylene diimides (PDI) leads to the efficient passivation of BP field effect transistors (FET). This straightforward wet chemical approach allows to preserve the electronic properties under environmental conditions. More details can be found in article number 2001290 by Gonzalo Abellán, Andreas Hirsch, and co-workers.

Sensitive detection of water/oxygen molecule adsorption and reaction on a titanium oxide nanosheet with a graphene field effect transistor

We have investigated molecule adsorption phenomena on a chemically active surface of titanium oxide nanosheet by coupling with an electrically sensitive graphene field effect transistor (FET). Super-hydrophilic surface of the titanium oxide nanosheet forms a water-layer in ambient air which exhibits a large hysteresis of drain current in the hybrid FET for sweeping gate-voltage. The large hysteresis disappears in vacuum, which indicates physically adsorbed water molecules on the surface of the titanium oxide nanosheet dominantly contribute to the hysteresis. UV light irradiation in vacuum significantly changes the drain current due to desorption of the adsorbed molecules. Sufficient UV irradiation results in symmetric gate-voltage dependence similar to those of conventional graphene FETs. Exposure to an oxygen gas atmosphere leads to a heavy hole doping in the FET, where the binding of the oxygen molecules is stronger than that of water molecules. In a humidified nitrogen atmosphere, a large shift of charge neutrality point is observed in transfer characteristics crossing between electron doping and hole doping. By contrast, a clear square-shaped hysteresis loop is observed in a humidified oxygen atmosphere, where the hole density in the graphene drastically changed with O2/H2O redox couple reaction on the titanium oxide nanosheet.

Noncovalent Functionalization and Passivation of Black Phosphorus with Optimized Perylene Diimides for Hybrid Field Effect Transistors

AbstractAmongst the different existing methods to passivate black phosphorus (BP) from environmental degradation, the noncovalent functionalization with perylene diimides (PDI) has been postulated as one of the most promising routes because it allows preserving its electronic properties. This work describes the noncovalent functionalization and outstanding environmental protection of BP with tailor made PDI having peri‐amide aromatic side chains, which include phenyl and naphthyl groups, exhibiting a significantly increased molecule‐BP interaction. These results are rationalized by density functional theory (DFT) calculations showing that the adsorption energies are mainly governed by van der Waals (vdW) interactions and increase concomitantly with the aromatic character of the side chains. The resulting hybrids are thoroughly characterized showing enhanced ambient and thermal stabilities. Last but not least, hybrid organic–inorganic BP‐PDI field effect transistors (FETs) are studied for the first time showing the usefulness of PDI derivatives as efficient passivation layers while obtaining improved values of electron mobilities. These results pave the way for the use of optimized PDIs by molecular engineering to preserve the electronic properties of BP FETs, using straightforward wet chemical approaches.

Giant tunability in electrical contacts and doping via inconsiderable normal electric field strength or gating for a high-performance in ultrathin field effect transistors based on 2D BX/graphene (X = P, As) van der Waals heterobilayer

Electrical contacts arising at the van der Waals interface between boron pnictide (h-BP, h-BAs) and graphene monolayers have been systematically investigated using density functional theory. The electronic band structure of the individual monolayers is well preserved in the heterostructures constituted from them, indicating a weak van der Waals (vdW) interaction between them. BP monolayer is found to form n-type Schottky contact with a Schottky barrier height (SBH) of 0.4 eV in BP/graphene van der Waals heterostructure (vdWH), whereas a small p-type SBH of 0.16 eV occurs at BAs/graphene vdWH. The SBHs obtained for BX/graphene are lower than that of other transition metal dichalcogenide based graphene vdWH and electrical properties are found to be significantly tunable/transformable via small applied electric field of ±0.15 V/Å. These insightful results will motivate experimentalists and technologists to design high performance graphene-based hybrid field-effect transistors (FET). Also, the vdWHs are found to show significant robustness, structural integrity and flexibility. The bending modulus of BP (As)/graphene is found to be lower than that in graphene/MoS2. The graphene/h-BN vdWH has been experimentally studied, while the thin films of h-BP have been recently synthesized; thereby substantiating the experimental feasibility in building up the heterostructures proposed in this work.

Ultrathin MoOx/Graphene Hybrid Field Effect Transistor Sensors Prepared Simply by a Shadow Mask Approach for Selective ppb‐Level NH3 Sensing with Simultaneous Superior Response and Fast Recovery

AbstractBoth simultaneous achievement of high response, low limit of detection, and full recovery at room temperature (RT) for weak reducing gases like NH3 and facile and batchable fabrication approach are quite challenging for sensors. Herein, ultrathin MoOx layers are hybridized with mono layer graphene with different coverage percentages, into MoOx/GFET (graphene field effect transistor) devices for selective NH3 sensing fabricated by a facile, cost effective, and contamination‐free shadow mask approach instead of conventional lithography processes. A response of −18.10% for 12 ppm NH3 with full recovery of 356 s, superior repeatability, low detection limit of 310 ppb, and strong selectivity is simultaneously achieved for MoOx/GFET sensors at RT. The superior sensing and recovery performance of MoOx/GFET sensors is predominantly attributed to the effective tuning of Schottky barrier height and the Coulomb interaction between charged polar donor molecules and positively polarized surface enhanced by the positive bias voltage. The energy band diagrams well explain the sensing mechanism for reducing/oxidizing gases. The idea proposed in this study offers a feasible solution for highly selective sensing of different gases by oxides/graphene hybrid FET based gas sensors with superior RT performances fabricated by a facile, contamination‐free, batchable, and generalized approach.

High-performance monolayer MoS2 field-effect transistor with large-scale nitrogen-doped graphene electrodes for Ohmic contact

A finite Schottky barrier and large contact resistance between monolayer MoS2 and electrodes are the major bottlenecks in developing high-performance field-effect transistors (FETs) that hinder the study of intrinsic quantum behaviors such as valley-spin transport at low temperature. A gate-tunable graphene electrode platform has been developed to improve the performance of MoS2 FETs. However, intrinsic misalignment between the work function of pristine graphene and the conduction band of MoS2 results in a large threshold voltage for the FETs, because of which Ohmic contact behaviors are observed only at very high gate voltages and carrier concentrations (∼1013 cm−2). Here, we present high-performance monolayer MoS2 FETs with Ohmic contact at a modest gate voltage by using a chemical-vapor-deposited (CVD) nitrogen-doped graphene with a high intrinsic electron carrier density. The CVD nitrogen-doped graphene and monolayer MoS2 hybrid FETs platform exhibited a large negative shifted threshold voltage of −54.2 V and barrier-free Ohmic contact under zero gate voltage. Transparent contact by nitrogen-doped graphene led to a 214% enhancement in the on-current and a fourfold improvement in the field-effect carrier mobility of monolayer MoS2 FETs compared with those of a pristine graphene electrode platform. The transport measurements, as well as Raman and X-ray photoelectron spectroscopy analyses before and after thermal annealing, reveal that the atomic C-N bonding in the CVD nitrogen-doped graphene is responsible for the dominant effects of electron doping. Large-scale nitrogen-doped graphene electrodes provide a promising device platform for the development of high-performance devices and the study of unique quantum behaviors.

Toward a highly selective artificial saliva sensor using printed hybrid field effect transistors

Ion selective field effect transistors (ISFETs) have been widely used in the biological and environmental sensing applications. However, the rigid feature of common ISFETs blocked the real-time monitoring applications. Here, we report a feasible 3D printing method to fabricate flexible ISFETs by hybridization of printed organic ion selective electrodes and inorganic transistors. The fabricated ISFETs demonstrated high sensitivity, ranged about 100 mV/decade, towards ions such as ammonium (NH4+), potassium (K+), and calcium (Ca2+). Furthermore, the fabricated hybrid ISFETs showed their distinct selectivity from the mixture of varied interference ions as an artificial saliva. This capability provides an integrated platform for a comprehensive ion analysis by closely monitoring interrelated saliva parameters as wearable healthcare solutions manufactured by 3D printing methods.

Room-temperature electrically driven phase transition of two-dimensional 1T-TaS2 layers.

Due to the strong electron-electron and electron-phonon interactions, the transition metal dichalcogenide 1T-TaS2 exhibits temperature dependent as well as electric field driven charge density wave (CDW) phase transitions (PTs). In this work, we investigate the thickness dependence of the electric field driven PT in 1T-TaS2 two-dimensional (2D) flakes. Electrically driven PT between high- and low-resistance states occurs at temperatures in the range of 60-300 K. For a thin 1T-TaS2 (≤8.8 nm) sample, only one PT is triggered, whereas thick films experience double PTs (13-17 nm) and multiple PTs (≥17.5 nm) until reaching the final low-resistance state. The multiple PTs may imply the existence of hidden nearly-commensurate charge density wave (NCCDW) states. In addition, a threshold electric field is observed, in which the low-resistance state is unable to resume the high-resistance state. Finally, we fabricate a 1T-TaS2/graphene hybrid field effect transistor to achieve a gate-tunable PT at room temperature. Such a hybrid device might provide a new avenue for the construction of CDW-based memories based on 2D materials.

Flexible Organic/Inorganic Hybrid Field-Effect Transistors with High Performance and Operational Stability.

The production of high-quality semiconducting nanostructures with optimized electrical, optical, and electromechanical properties is important for the advancement of next-generation technologies. In this context, we herein report on highly obliquely aligned single-crystalline zinc oxide nanosheets (ZnO NSs) grown via the vapor-liquid-solid approach using r-plane (01-12) sapphire as the template surface. The high structural and optical quality of as-grown ZnO NSs has been confirmed using high-resolution transmission electron microscopy and temperature-dependent photoluminescence, respectively. To assess the potential of our NSs as effective building materials in high-performance flexible electronics, we fabricate organic (parylene C)/inorganic (ZnO NS) hybrid field-effect transistor (FET) devices on flexible substrates using room-temperature assembly processes. Extraction of key FET performance parameters suggests that as-grown ZnO NSs can successfully function as excellent n-type semiconducting modules. Such devices are found to consistently show very high on-state currents (Ion) > 40 μA, high field-effect mobility (μeff) > 200 cm2/(V s), exceptionally high on/off current modulation ratio (Ion/off) of around 109, steep subthreshold swing (s-s) < 200 mV/decade, very low hysteresis, and negligible threshold voltage shifts with prolonged electrical stressing (up to 340 min). The present study delivers a concept of integrating high-quality ZnO NS as active semiconducting elements in flexible electronic circuits.

Rational design of multifunctional devices based on molybdenum disulfide and graphene hybrid nanostructures

We rationally designed a new type of hybrid materials, molybdenum disulfide (MoS2) synthesized by Mo pre-deposition followed by subsequent sulfurization process directly on thermal chemical vapor deposition (TCVD)-grown graphene, for applications in a multifunctional device. The synthesis of stoichiometric and uniform multilayer MoS2 and high-crystalline monolayer graphene was evaluated by X-ray photoelectron spectroscopy and Raman spectroscopy. To examine the electrical transport and photoelectrical properties of MoS2-graphene hybrid films, field effect transistors (FETs) and visible-light photodetectors based on MoS2-graphene were both fabricated. As a result, the extracted mobility for MoS2-graphene hybrid FETs was two times higher than that of MoS2 FETs. In addition, the MoS2-graphene photodetectors revealed a significant photocurrent with abrupt switching behavior under periodic illumination.

Proposal of a GaN/SiC Hybrid Field-Effect Transistor for Power Switching Applications

A GaN/SiC hybrid field-effect transistor (HyFET) is proposed as a high-voltage power device that provides a high-mobility lateral AlGaN/GaN channel to reduce the channel resistance and a vertical SiC drift region to sustain the high OFF-state voltage. The performance of the HyFET is evaluated by numerical device simulations. Compared with the conventional SiC MOSFET, the HyFET exhibits a greatly reduced $R_{\mathrm{\scriptscriptstyle ON}}$ together with a low $C_{\mathrm{ GD}}$ and low gate charges. The figures of merit $Q_{\mathrm{ G}}\times R_{\mathrm{\scriptscriptstyle ON}}$ and $Q_{\mathrm{ GD}}\times R_{\mathrm{\scriptscriptstyle ON}}$ of the HyFET are dramatically improved.

Photosensitive cadmium telluride thin-film field-effect transistors.

We report on the graphene-seeded growth and fabrication of photosensitive Cadmium telluride (CdTe)/graphene hybrid field-effect transistors (FETs) subjected to a post-growth activation process. CdTe thin films were selectively grown on pre-defined graphene, and their morphological, electrical and optoelectronic properties were systemically analyzed before and after the CdCl2 activation process. CdCl2-activated CdTe FETs showed p-type behavior with improved electrical features, including higher electrical conductivity (reduced sheet resistance from 1.09 × 10(9) to 5.55 × 10(7) Ω/sq.), higher mobility (from 0.025 to 0.20 cm2/(V·s)), and faster rise time (from 1.23 to 0.43 s). A post-growth activation process is essential to fabricate high-performance photosensitive CdTe/graphene hybrid devices.

Ultrasensitive Mercury Ion Detection Using DNA-Functionalized Molybdenum Disulfide Nanosheet/Gold Nanoparticle Hybrid Field-Effect Transistor Device

Mercury, one of the most harmful pollutants in water, has a significant negative impact on human health. The molybdenum disulfide (MoS2) nanosheet, due to its unique electronic properties, is a promising candidate for high-performance sensing materials. Here, we report a DNA-functionalized MoS2 nanosheet/gold nanoparticle hybrid field-effect transistor (FET) sensor for the ultrasensitive detection of Hg2+ in an aqueous environment. Specific DNA was used in the hybrid structure as the capture probe for the label-free detection. By monitoring the electrical characteristics of the FET device, the performance of the sensor was investigated. Our sensor shows a rapid response (1–2 s) to Hg2+ and an ultralow detection limit of 0.1 nM, which is much lower than the maximum contaminant level (MCL) for Hg2+ in drinking water (9.9 nM) recommended by the U.S. Environmental Protection Agency (EPA). In addition, the sensor shows a high selectivity to Hg2+ compared with other interfering metal ions, e.g., As5+, Cd2+, Pb2...

High-Performance Flexible Ultraviolet (UV) Phototransistor Using Hybrid Channel of Vertical ZnO Nanorods and Graphene

A flexible ultraviolet (UV) photodetector based on ZnO nanorods (NRs) as nanostructure sensing materials integrated into a graphene (Gr) field-effect transistor (FET) platform is investigated with high performance. Based on the negative shift of the Dirac point (VDirac) in the transfer characteristics of a phototransistor, high-photovoltage responsivity (RV) is calculated with a maximum value of 3 × 10(8) V W(-1). The peak response at a wavelength of ∼365 nm indicated excellent selectivity to UV light. The phototransistor also allowed investigation of the photocurrent responsivity (RI) and photoconductive gain (G) at various gate voltages, with maximum values of 2.5 × 10(6) A W(-1) and 8.3 × 10(6), respectively, at a gate bias of 5 V. The UV response under bending conditions was virtually unaffected and was unchanged after 10,000 bending cycles at a bending radius of 12 mm, subject to a strain of 0.5%. The attributes of high stability, selectivity, and sensitivity of this flexible UV photodetector based on a ZnO NRs/Gr hybrid FET indicate promising potential for future flexible optoelectronic devices.