Channel Of Field Effect Transistor Research Articles

Engineering MoSe2/MoS2 heterojunction traps in 2D transistors for multilevel memory, multiscale display, and synaptic functions

We study a low voltage short pulse operating multilevel memory based on van der Waals heterostack (HS) n-MoSe2/n-MoS2 channel field-effect transistors (FETs). Our HS memory FET exploited the gate voltage (VGS)-induced trapping/de-trapping phenomena for Program/Erase functioning, which was maintained for long retention times owing to the existence of heterojunction energy barrier between MoS2 and MoSe2. More interestingly, trapped electron density was incrementally modulated by the magnitude or cycles of a pulsed VGS, enabling the HS device to achieve multilevel long-term memory. For a practical demonstration, five different levels of drain current were visualized with multiscale light emissions after our memory FET was integrated into an organic light-emitting diode pixel circuit. In addition, our device was applied to a synapse-imitating neuromorphic memory in an artificial neural network. We regard our unique HS channel FET to be an interesting and promising electron device undertaking multifunctional operations related to the upcoming fourth industrial revolution era.

The effect of nonideal boundary condition on instability of THz plasma waves in quantum field-effect transistors

The instability of THz plasma waves propagating along a channel of field-effect transistors opens up a new mechanism of emission of THz waves. In this work, we investigate the instability of THz plasma waves in field-effect transistors in the presence of quantum effects and nonideal boundary condition at the source and the drain by using the quantum hydrodynamic model. The results show that the THz plasma waves will be unstable when the gate–source capacitances are larger than gate–drain capacitances and the instability increment can be increased by increasing gate–source capacitances or decreasing gate–drain capacitances. The results of this work give nano-field-effect transistors an advantage in achieving real THz oscillations.

Vertical organic phototransistors realized by femtosecond laser ablation patterned metal/insulator bilayer source electrodes: Performance and numerical modeling

Compared with their conventional lateral counter parts, vertical organic phototransistors (VOPTs) have the advantage of fast response speed due to short channel lengths, and may find wide applications in the field of high speed photo detection. By operation of VOPTs, the source electrode plays the vital role. We report on fabrication, characterization and analysis of VOPTs with pulsed laser ablation patterned Al/LiF bilayer source electrode. A maximal photoresponsivity of 760 mA/W, external quantum efficiency ( EQE ) of 145%, specific detectivity of 1.6 × 10 11 Jones were obtained for un-optimized devices. For describing the output characteristics of the devices, a rough numerical model was developed by combining the theory of thermionic emission at metal/organic interface and space charge limited current conduction. • We innovatively achieved the manufacture of vertical channel field-effect transistors by using a porous metal/insulator bilayer source electrode. • We patterned the porous electrode by femtosecond laser ablation. • We proposed a phenomenological device model to getting quantitative insight into the working mechanism of VOPTs. • The un-optimized device in this work showed a maximal photoresponsivity of 760 mA/W, EQE of 145%, specific detectivity of 1.6 × 10 11 Jones.

Wrapped Channel FET (WCFET)

In this article, we examined the electrical characteristic of proposed new device structure, Wrapped Channel Field Effect Transistor (WCFET). Results of WCFET have been analyzed using Atlas 3-D simulator. WCFET shows better transfer characteristics with ON-current ION of ~10-6A and leakage current IOFF of ~10-16 A. Optimization of device characteristics has done with doping concentration (ND), gate work function (ΦG) and spacer dielectric. Impact of gate length and semiconductor film thickness variation on drain current, subthreshold slope (SS) and DIBL are also investigated. Further, effects of various gate dielectric materials such as SiO2, Si3N3, HfO2 and TiO2 are examined w.r.t. switching characteristics of WCFET. To validate of device compatibility with power supply scaling, we inspected full range variation of VDS ≈ (0.05V-to-0.7V) on transfer characteristics.

Effect of fluorine–fluorine repulsive coupling on charge transport in cyclopentadithiophene-based donor–acceptor-type conjugated copolymer films

This study elucidates the effect of fluorine–fluorine interactions on the charge transport properties of semiconductor channels in polymer-based field effect transistors (PFETs) in which both a donor–acceptor (D–A)-type conjugated polymer and a polymer dielectric material contain fluorinated units. The fluorinated units on the benzothiadiazole (BTZ) block of cyclopentadithiophene- alt -benzothiadiazole (CDT-BTZ) allow conformation locking via F⋯S nonbonding interactions, which increases the planarity of cyclopentadithiophene- alt -fluoro-2,1,3-benzothiadiazole (CDT-FBTZ). Thus, the CDT-FBTZ copolymer films are highly crystalline and adopt the edge-on orientation, resulting in an eight-fold increase in the field-effect mobility for CDT-FBTZ-based PFETs coated with a poly(methyl methacrylate) (PMMA) dielectric layer compared with PMMA-coated CDT-BTZ-based PFETs. Meanwhile, the field-effect mobility of CDT-BTZ-based PFETs containing a fluorinated dielectric polymer (CYTOP) is double that of PMMA-coated CDT-BTZ-based PFETs. These enhanced electrical properties are attributed to surface polarization doping at the interface between the conjugated polymer and the fluorinated polymer dielectric. However, despite the effect of surface polarization doping, the electrical properties of CDT-FBTZ-based PFETs deteriorate when combined with the fluorinated CYTOP dielectric. Charge transport analyses based on the Gaussian disorder model reveal that, for CDT-based D–A-type conjugated copolymer PFETs, very few localized states in the semiconducting channel of PFET devices in which fluorine–fluorine interaction effects occur at the interface switch to delocalized states as the gate-bias increases. In contrast, the localized charge states in PFET channels without fluorine–fluorine interactions depend strongly on the applied gate-bias and become delocalized upon applying a gate-bias. Thus, it is inferred that the fluorine–fluorine repulsive coupling in D–A-type conjugated copolymers containing fluorinated functional moieties that interface with fluorinated polymer dielectric layers hinders the delocalization of charges induced by the gate-bias, thereby degrading the device performance. • Effect of fluorine–fluorine interactions on charge transport in polymer transistors investigated. • High-performance polymer field effect transistor obtained using fluorinated polymer. • Temperature-variable current-voltage analyses of the devices conducted. • Electrical degradation of polymer transistor caused by the fluorine–fluorine interactions.

Modeling and characterization of optimal nano-scale channel dimensions for fin field effect transistor based on constituent semiconductor materials

This study aims to design an optimal nano-dimensional channel of fin field effect transistor (FinFET) on the basis of electrical characteristics and constituent semiconductor materials (Si, GaAs, Ge, and InAs) to overcome issues regarding the shrinking of dimensions and ensure the best performance of FinFETs. This objective has been achieved by proposing a new scaling factor, K, to simultaneously shrink the physical scaling limits of channel dimensions for various FinFETs without degrading their performance. A simulation-based comprehensive comparative study depending on four variable parameters (length, width, oxide thickness of the channel, and scaling factor) was carried out. The influence of changing channel dimensions on the performance of each type of FinFET was evaluated according to four electrical characteristics: i) ON-state/OFF-state current (ION/IOFF) ratio, ii) subthreshold swing (SS), iii) threshold voltage, and iv) drain-induced barrier lowering. The well-known multi-gate field-effect transistor (MuGFET) simulation tool for nanoscale MuGFET structure was utilized to conduct experimental simulations under the considered conditions. The obtained simulation results showed that the optimal channel dimensions for the best performance of all considered FinFET types were achieved at a minimal scaling factor K=0.125 with 5 nm length, 2.5 nm width, and 0.625 nm oxide thickness of the channel.

Improvement in carrier mobility through band-gap engineering in atomic-layer-deposited In-Ga-Zn-O stacks

This paper reports the performance improvement of heterojunction channel field-effect transistor using an atomic-layer-deposited InGaZnO (IGZO) channel on basis of a band alignment. The heterojunction stack consisted of a 5 nm-thick In0.61Ga0.16Zn0.23O confinement layer (CL) and a 2 nm-thick In0.52Ga0.32Zn0.15O barrier layer (BL). Band-gap engineering through cation composition and thickness modulation of each layers allowed free electron diffusion from the In0.52Ga0.32Zn0.15O BL to the In0.61Ga0.16Zn0.23O CL and carriers confinement in CL, leading to the improvement in field-effect mobility. The control transistor with 5 nm-thick IGZO CL layer had a mobility of 33.4 cm2/Vs, whereas the heterojunction transistor with 2 nm-thick IGZO BL exhibited a higher mobility of 50.7 cm2/Vs as well as low gate swing of 89 mV/decade as a result of carrier transporting boosting. Moreover, the corresponding heterojunction channel transistors exhibited better gate bias stability due to the mitigation of gap states creation and passivating behavior by introducing the 2 nm-thick IGZO BL.

Damage-Free Charge Transfer Doping of 2D Transition Metal Dichalcogenide Channels by van der Waals Stamping of MoO3 and LiF.

To dope 2D semiconductor channels, charge-transfer doping has generally been done by thermal deposition of inorganic or organic thin-film layers on top of the 2D channel in bottom-gate field-effect transistors (FETs). The doping effects are reproducible in most cases. However, such thermal deposition will damage the surface of 2D channels due to the kinetic energy of depositing atoms, causing hysteresis or certain degradation. Here, a more desirable charge-transfer doping process is suggested. A damage-free charge-transfer doping is conducted for 2D MoTe2 (or MoS2 ) channels using a polydimethylsiloxane stamp. MoO3 or LiF is initially deposited on the stamp as a doping medium. Hysteresis-minimized transfer characteristics are achieved from stamp-doped FETs, while other devices with direct thermal deposition-doped channels show large hysteresis. The stamping method seems to induce a van der Waals-like damage-free interface between the channel and doping media. The stamp-induced doping is also well applied for a MoTe2 -based complementary inverter because MoO3 - and LiF-doping by separate stamps effectively modifies two ambipolar MoTe2 channels to p- and n-type, respectively.

Mixed-Dimensional 1D/2D van der Waals Heterojunction Diodes and Transistors in the Atomic Limit.

Inverting a semiconducting channel is the basis of all field-effect transistors. In silicon-based metal-oxide-semiconductor field-effect transistors (MOSFETs), a gate dielectric mediates this inversion. Access to inversion layers may be granted by interfacing ultrathin low-dimensional semiconductors in heterojunctions to advance device downscaling. Here we demonstrate that monolayer molybdenum disulfide (MoS2) can directly invert a single-walled semiconducting carbon nanotube (SWCNT) transistor channel without the need for a gate dielectric. We fabricate and study this atomically thin one-dimensional/two-dimensional (1D/2D) van der Waals heterojunction and employ it as the gate of a 1D heterojunction field-effect transistor (1D-HFET) channel. Gate control is based on modulating the conductance through the channel by forming a lateral p-n junction within the CNT itself. In addition, we observe a region of operation exhibiting a negative static resistance after significant gate tunneling current passes through the junction. Technology computer-aided design (TCAD) simulations confirm the role of minority carrier drift-diffusion in enabling this behavior. The resulting van der Waals transistor architecture thus has the dual characteristics of both field-effect and tunneling transistors, and it advances the downscaling of heterostructures beyond the limits of dangling bonds and epitaxial constraints faced by III-V semiconductors.

Optimization of channel structure and bias condition for signal-to-noise ratio improvement in Si-based FET-type gas sensor with horizontal floating-gate

Sensing performances of the Si-based field-effect transistor (FET)-type gas sensor are not only affected by sensing material characteristics but also by electrical properties of a transducer. Therefore, the optimization of transducer properties, including subthreshold swing, transconductance, and low-frequency noise (LFN) characteristics, is necessary for improving the sensing performances. In this paper, NO2 gas sensing properties, LFN characteristics, and signal-to-noise ratio (SNR) of the FET-type gas sensor having different channel structures (surface and buried channel FETs) are investigated. An n-type indium-gallium-zinc oxide (IGZO) thin-film is used as a sensing layer. The LFN characteristics of both sensors are explained using a carrier number fluctuation model with correlated mobility fluctuation. The flat-band voltage fluctuation (SVfb) value of the buried channel (4.54×10−10 V2/Hz) is smaller than that of the surface channel (2.73×10−9 V2/Hz). Thus, the SNR of the sensor with a buried channel shows ~10 times larger SNR than that with a surface channel. Also, the optimal bias conditions for both sensors are suggested. The sensor with buried channel FET has a limit of detection (LOD) of 44.2 ppt to NO2 gas.

SELECTIVE HIGH-SENSITIVITY RADIOMETER SWITCHING FREQUENCY AMPLIFIER WITH FREQUENCY RESPONSE TEMPERATURE COMPENSATION

Problems. It is noted that the measurement of low-intensity microwave signals of various physical bodies and biological objects is associated with the need to provide high sensitivity, which can reach 10-14 -10-15 watts. The authors of the article studied the selective (selective) filter-amplifier of the switching frequency of the high-sensitivity modulation radiometer as one of the elements that have a significant impact on the sensitivity and accuracy of measurement, and developed recommendations for improving the stability of its parameters.
 The purpose of the research. The peculiarities of the modulation radiometer conversion channel operation are considered and the role of the selective switching frequency amplifier in providing such sensitivity is determined.
 The input and output signals of the selective amplifier, their relationship and the effect on the sensitivity of the radiometer were obtained and analyzed. The necessity of application of compensation of influence of temperature on characteristics of the filter taking into account temperature coefficients of elements of the scheme is proved.
 Conclusions. Modeling of a selective amplifier with a third-order filter was performed, the amplitude-frequency characteristic and the zone of its possible displacement at the maximum operating temperature were obtained.
 The structural and schematic diagram of the selective amplifier with automatic consideration of temperature influences, due to the introduction of feedback and correction of the frequency response of the filter has been developed.
 The main parameters of the bandpass filter built on the feedback circuit are determined. The use of a field-effect transistor channel connected in series with the resistors of the frequency-forming circuits of the third-order filter is proposed as an element of frequency response correction.
 The technical requirements for modeling and development of a selective amplifier are determined, which provide opportunities for implementation in practice. The research can be used to build a highly sensitive radiometric system for measuring low-intensity signals in areas such as biology and medicine.

Effect of Al2O3 Passive Layer on Stability and Doping of MoS2 Field-Effect Transistor (FET) Biosensors.

Molybdenum disulfide (MoS2) features a band gap of 1.3 eV (indirect) to 1.9 eV (direct). This tunable band gap renders MoS2 a suitable conducting channel for field-effect transistors (FETs). In addition, the highly sensitive surface potential in MoS2 layers allows the feasibility of FET applications in biosensors, where direct immobilization and detection of biological molecules are conducted in wet conditions. In this work, we report, for the first time, the degradation of chemical vapor deposition (CVD) grown MoS2 FET-based sensors in the presence of phosphate buffer and water, which caused false positive response in detection. We conclude the degradation was originated by physical delamination of MoS2 thin films from the SiO2 substrate. The problem was alleviated by coating the sensors with a 30 nm thick aluminum oxide (Al2O3) layer using atomic layer deposition technique (ALD). This passive oxide thin film not only acted as a protecting layer against the device degradation but also induced a strong n-doping onto MoS2, which permitted a facile method of detection in MoS2 FET-based sensors using a low-power mode chemiresistive I-V measurement at zero gate voltage (Vgate = 0 V). Additionally, the oxide layer provided available sites for facile functionalization with bioreceptors. As immunoreaction plays a key role in clinical diagnosis and environmental analysis, our work presented a promising application using such enhanced Al2O3-coated MoS2 chemiresistive biosensors for detection of HIgG with high sensitivity and selectivity. The biosensor was successfully applied to detect HIgG in artificial urine, a complex matrix containing organics and salts.

The emission of THz plasma waves in graphene field-effect transistors with quantum effects

The instability of electron fluid in the channel of graphene field-effect transistors has provided a powerful theoretical basis for the radiation and detection of THz waves. In this paper, the quantum hydrodynamic model governing the characteristics of two electron gas in channel of graphene field-effect transistors is presented. The instability of THz plasma waves is analyzed in the presence of boundary condition with quantum effects. The results show that the strength of quantum effects will lead to an increase in oscillation frequency and instability increment of THz plasma oscillation in graphene field-effect transistors. These properties could make the nanometer graphene field-effect transistors advantageous for realization of practical terahertz oscillations.

Plasmonic Field-Effect Transistors (TeraFETs) for 6G Communications.

Ever increasing demands of data traffic makes the transition to 6G communications in the 300 GHz band inevitable. Short-channel field-effect transistors (FETs) have demonstrated excellent potential for detection and generation of terahertz (THz) and sub-THz radiation. Such transistors (often referred to as TeraFETs) include short-channel silicon complementary metal oxide (CMOS). The ballistic and quasi-ballistic electron transport in the TeraFET channels determine the TeraFET response at the sub-THz and THz frequencies. TeraFET arrays could form plasmonic crystals with nanoscale unit cells smaller or comparable to the electron mean free path but with the overall dimensions comparable with the radiation wavelength. Such plasmonic crystals have a potential of supporting the transition to 6G communications. The oscillations of the electron density (plasma waves) in the FET channels determine the phase relations between the unit cells of a FET plasmonic crystal. Excited by the impinging radiation and rectified by the device nonlinearities, the plasma waves could detect both the radiation intensity and the phase enabling the line-of-sight terahertz (THz) detection, spectrometry, amplification, and generation for 6G communication.

Optimization of Self-Heating Driven Leakage Current Properties of Gate-All-Around Field-Effect Transistors Using Neural Network Modeling and Genetic Algorithm

As the technology nodes of semiconductor devices have become finer and more complex, progressive scaling down has been implemented to achieve higher densities for electronic devices. Thus, three-dimensional (3D) channel field-effect transistors (FETs), such as fin-shaped FETs (FinFETs) and gate-all-around FETs (GAAFETs), have become popular as they have increased effective surface areas for the channels (Weff), owing to the scaling down strategy. These 3D channel FETs, which have completely covered channel structures with gate oxide and metal, are prone to the self-heating effect (SHE). The SHE is generally known to degrade the on-state drain current; however, when AC pulsed inputs are applied to these devices, the SHE also degrades the off-state leakage current during the off-phase of the pulse. In this study, an optimization methodology to minimize leakage current generation by the SHE is examined.

Implementation of 20 nm Graphene Channel Field Effect Transistors Using Silvaco TCAD Tool to Improve Short Channel Effects over Conventional MOSFETs

In recent years, demands for high speed and low power circuits have been raised. As conventional metal oxide semiconductor field effect transistors (MOSFETs) are unable to satisfy the demands due to short channel effects, the purpose of the study is to design an alternative of MOSFETs. Graphene FETs are one of the alternatives of MOSFETs due to the excellent properties of graphene material. In this work, a user-defined graphene material is defined, and a graphene channel FET is implemented using the Silvaco technology computer-aided design (TCAD) tool at 100 nm and scaled to 20 nm channel length. A silicon channel MOSFET is also implemented to compare the performance. The results show the improvement in subthreshold slope (SS) = 114 mV/dec, ION/IOFF ratio = 14379, and drain induced barrier lowering (DIBL) = 123 mV/V. It is concluded that graphene FETs are suitable candidates for low power applications.

Paving the Way for Tunable Graphene Plasmonic THz Amplifiers

This study reviews recent advances in room-temperature coherent amplification of terahertz (THz) radiation in graphene, electrically driven by a dry cell battery. Our study explores THz light–plasmon coupling, light absorption, and amplification using a current-driven graphene-based system because of its excellent room temperature electrical and optical properties. An efficient method to exploit graphene Dirac plasmons (GDPs) for light generation and amplification is introduced. This approach is based on current-driven excitation of the GDPs in a dual-grating-gate high-mobility graphene channel field-effect transistor (DGG-GFET) structure. The temporal response of the DGG-GFETs to the polarization-managed incident THz pulsation is experimentally observed by using THz time-domain spectroscopy. Their Fourier spectra of the transmitted temporal waveform through the GDPs reveals the device functions 1) resonant absorption at low drain bias voltages below the first threshold level, 2) perfect transparency between the first and the second threshold drain bias levels, and 3) resonant amplification beyond the second threshold drain bias voltage. The maximal gain of 9% is obtained by a monolayer graphene at room temperatures, which is four times higher than the quantum limit that is given when THz photons directly interact with electrons. The results pave the way toward tunable graphene plasmonic THz amplifiers.

Ionic Liquid Channel Field Effect Transistor Fabricated Using Silicon Dioxide Trench

This work explores the fabrication and characterization of an ionic liquid channel field effect transistor (FET) incorporated within the trench structure on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The trench structure allows any liquid to be accommodated, thereby eliminating the mold creation on the device or the requirement for an intricate architecture to store liquid. For the fabrication of the trench, we followed a standard photolithography process with the help of selective etching of aluminum and SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The fabricated trench surface is characterized using atomic force microscopy (AFM) and contact angle analysis. The electrical characterization of the proposed FET structure is also performed with 0.01-mM potassium chloride (KCl) solution as an ionic channel. We tested both the n-FET and p-FET type characteristics which can be controlled by the back gate biasing condition. The dc characterization shows a high I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ratio of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> for both the n-FET and p-FET. The device further shows an improvement in K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> mobility and Cl <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> mobility of 2.24 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs and 4.96 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs, respectively. We also carried out the FET structure modeling to estimate the effective C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ox</sub> for the trench SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> structure. It is observed that the total capacitance after the inclusion of Debye length is 1.29 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> F/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Furthermore, the number of ions is also calculated from the electrical characteristics, and it is almost comparable with the number of ions in the molar solution. Overall, the proposed fabricated structure, although simple, enables to accommodate any liquid as a channel and provides an easy way to develop electrolyte-based sensors.

Transient performance analysis of graphene FET gated via ionic solid by numerical simulations based on tight-binding method and Nernst–Planck–Poisson equations

We investigate the electrical transport characteristics of graphene channel field-effect transistors (FETs) gated via ionic solid (IS), where the conventional gate insulator, such as SiO2, has been replaced by solid electrolytes, such as LiP3O4. In this study, we focus on (i) the gate controllability of the current in comparison to conventional graphene FETs with SiO2 as an insulating material and (ii) the transient characteristics of the drain current and time required to switch on the current. We employ the tight-binding formalism and Boltzmann equation to calculate the electronic band structure and the electronic transport in graphene, while the Nernst–Planck–Poisson equations have been employed to calculate the time-dependent charge distribution in solid electrolytes and the resulting electric double layer formation at the graphene/IS and IS/gate interfaces. Our simulations have shown that graphene FET gated via IS shows superior gate controllability more than SiO2-gated graphene FET with the insulator thickness of 1 nm, and the saturated drain current is insensitive to the IS thickness. Moreover, the time required to switch on the drain current is proportional to the thickness of IS, and the limited number of Li+ ion vacancies in IS is preferable in obtaining faster switching than the case of unlimited vacancy cases while keeping the superior gate controllability.

Ambipolar Channel p-TMD/n-Ga2 O3 Junction Field Effect Transistors and High Speed Photo-sensing in TMD Channel.

Highly crystalline 2D/3D-mixed p-transition metal dichalcogenide (TMD)/n-Ga2 O3 heterojunction devices are fabricated by mechanical exfoliation of each p- and n-type material. N-type β-Ga2 O3 and p-type TMD separately play as a channel for junction field effect transistors (JFETs) with each type of carriers as well as materials for a heterojunction PN diode. The work thus mainly focuses on such ambipolar channel transistors with two different types of channel in a single device architecture. For more extended applications, the transparency of high energy band gap β-Ga2 O3 (Eg ≈ 4.8eV) is taken advantage of, firstly to measure the electrical energy gap of p-TMDs receiving visible or near infrared (NIR) photons through the β-Ga2 O3 . Next, the p-TMD/n-Ga2 O3 JFETs are put to high speed photo-sensing which is achieved from the p-TMD channel under reverse bias voltages on n-Ga2 O3 . The photo-switching cutoff frequency appears to be ≈16 and 29kHz for visible red and NIR illuminations, respectively, on the basis of -3dB photoelectric power loss. Such a high switching speed of the JFET is attributed to the fast transport of photo-carriers in TMD channels. The 2D/3D-mixed ambipolar channel JFETs and their photo-sensing applications are regarded novel, promising, and practically easy to achieve.