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Ferroelectric field effect transistors (Fe-FETs) offer promising candidates for neuromorphic computing. However, it is still challenging to achieve a light-tunable field effect, which limits the function of photo-synapse. In this work, a ferroelectric semiconductor floating-gate transistor (FSF-FET) is proposed based on MoS2/h-BN/α-In2Se3 van der Waals heterojunctions (vdWHs), in which the two-dimensional ferroelectric semiconducting α-In2Se3 and dielectric h-BN serve as the trapped layer of charges and prevent layer, respectively. The excellent memory performances are exhibited, including a high programming/erasing ratio of over 107, a large memory window ratio of 74.69%, and good non-volatility. Moreover, the FSF-FETs also possess the light-tunable synapse behaviors, including the high paired-pulse facilitation of 236% and an obvious transition from short-term plasticity to long-term plasticity. The high recognition rate of 93.9% is achieved with dual-mode modulation of light and electrical pulses. The ferroelectric semiconductor floating-gate design opens up a strategy to realize the light-tunable field effect of Fe-FETs for photo-synapse. [ABSTRACT FROM AUTHOR]

We report on transport characteristics of field effect two-dimensional electron gases (2DEGs) in 24 nm wide indium arsenide surface quantum wells. High quality single-subband magnetotransport with clear quantized integer quantum Hall plateaus is observed to filling factor ν = 2 in magnetic fields of up to B = 18 T, at electron densities up to 8 × 10 11 /cm2. Peak mobility is 11 000 cm2/Vs at 2 × 10 12 /cm2. Large Rashba spin–orbit coefficients up to 124 meV Å are obtained through weak anti-localization measurements. Proximitized superconductivity is demonstrated in Nb-based superconductor-normal-superconductor (SNS) junctions, yielding 78%–99% interface transparencies from superconducting contacts fabricated ex situ (post-growth), using two commonly used experimental techniques for measuring transparencies. These transparencies are on a par with those reported for epitaxially grown superconductors. These SNS junctions show characteristic voltages I c R n up to 870 μV and critical current densities up to 9.6 μA/μm, among the largest values reported for Nb-InAs SNS devices. [ABSTRACT FROM AUTHOR]

Two-dimensional van der Waals ferroelectrics with in-plane polarization are less vulnerable to the depolarization field effect, making them practically more favorable in device applications. Herein, symmetric planar memristor based on two-dimensional van der Waals WO2Cl2 was fabricated and electrically characterized, showing significant memory effect with a current ON/OFF ratio up to 104 and stable switching cycles. Both short-term plasticity and long-term potentiation were observed in synaptic simulations by applying consecutive positive and negative pulses, respectively, which demonstrates the potential capability of this WO2Cl2 memristor in neuro-morphic computing as an artificial synapse. [ABSTRACT FROM AUTHOR]

Two-dimensional van der Waals ferroelectrics with in-plane polarization are less vulnerable to the depolarization field effect, making them practically more favorable in device applications. Herein, symmetric planar memristor based on two-dimensional van der Waals WO2Cl2 was fabricated and electrically characterized, showing significant memory effect with a current ON/OFF ratio up to 104 and stable switching cycles. Both short-term plasticity and long-term potentiation were observed in synaptic simulations by applying consecutive positive and negative pulses, respectively, which demonstrates the potential capability of this WO2Cl2 memristor in neuro-morphic computing as an artificial synapse. [ABSTRACT FROM AUTHOR]

Visible-light field effect phototransistors (FEPTs) with high detectivity and high speed are fabricated using a polarization induced photogate in a simple In0.15Ga0.85N/GaN heterostructure, where the pure polarization electric field acts as a virtual photogate of the FEPT and the total In0.15Ga0.85N layer plays the roles of absorber and channel. Experimental results show that the polarization electric field from high quality pseudo-crystalline InGaN/GaN structure can fully deplete the channel layer and leads to an ultra-low dark current. Furthermore, the channel conductivity can be significantly promoted with visible-light illumination. Therefore, the FEPT achieves a high visible-light gain of 6.0 × 104 and a superhigh shot noise limited specific detectivity of 1.5 × 1016 Jones, as well as a high speed with 15 ns/160 ns rise/fall time. The results not only present huge potential in visible-light photodetection, but also provide an insight into the application of polarization effects in wide bandgap semiconductors. [ABSTRACT FROM AUTHOR]

Herein, we examine the influence of controllable polarization reversal and built-in electric fields on pyroelectric and electrocaloric effects in a BaTiO3 thin film using a modified indirect method. We find that the magnitude of the sample's change in polarization with temperature is sensitive to the degree of polarization reversal. The pyroelectric response is small at low fractions of switched polarization and grows larger by several factors as larger fractions of polarization are reversed. This polarization reversal-sensitive pyroelectric behavior is the result of an internal built-in field, which has the effect of destabilizing low fractions of switched polarization and producing diminished pyroelectric effect. Greater fractions of switched polarization are more stable against backswitching and permit a larger pyroelectric response. Our findings highlight a characterization method for polarization-dependent pyroelectric effects in ferroelectric thin films, where built-in field effects are also present. [ABSTRACT FROM AUTHOR]

We report on transport characteristics of field effect two-dimensional electron gases (2DEGs) in surface indium antimonide quantum wells. The topmost 5 nm of the 30 nm wide quantum well is doped and shown to promote the formation of reliable, low resistance Ohmic contacts to surface InSb 2DEGs. High quality single-subband magnetotransport with clear quantized integer quantum Hall plateaus is observed to filling factor ν = 1 in magnetic fields of up to B = 18 T. We show that the electron density is gate-tunable, reproducible, and stable from pinch-off to 4 × 10 11 cm−2, and peak mobilities exceed 24 000 cm2/V s. Large Rashba spin–orbit coefficients up to 110 meV · Å are obtained through weak anti-localization measurements. An effective mass of 0.019me is determined from temperature-dependent magnetoresistance measurements, and a g-factor of 41 at a density of 3.6 × 10 11 cm−2 is obtained from coincidence measurements in tilted magnetic fields. By comparing two heterostructures with and without a delta-doped layer beneath the quantum well, we find that the carrier density is stable with time when doping in the ternary Al0.1In0.9Sb barrier is not present. Finally, the effect of modulation doping on structural asymmetry between the two heterostructures is characterized. [ABSTRACT FROM AUTHOR]

The anomalous droop in the external quantum efficiency (EQE) induced by the localization of excitons in GaN/InGaN green micro-light-emitting diodes (micro-LEDs) has been demonstrated at temperatures ranging from 25 to 100 K. At cryogenic temperatures, the random distribution of excitons among local potential energy minima limits the radiative recombination and reduces the EQE of green micro-LEDs. As the temperature increases from 25 to 100 K, the hopping of excitons from shallow potential energy minima to the potential energy valley contributes to the enhancement of radiative recombination. The distribution of excitons among local potential energy minima at cryogenic temperatures is also affected by the current density due to the influence of Coulomb screening of the polarization field and the band-filling effect. [ABSTRACT FROM AUTHOR]

In this Letter, we report the electrical performance improvement of indium oxide (In2O3) thin film transistors (TFTs) via a low-temperature CF4/N2O plasma treatment. It is found that the fluorination via CF4/N2O plasma can reduce the excessive electrons in the In2O3 channel more effectively compared to the oxidative annealing, providing the same low off-currents at a lower temperature of 200 °C, while the hydrogenation could not give rise to the off-current reduction. The fluorinated In2O3 TFTs with a channel thickness of 3.5 nm, a HfO2 dielectric thickness of 3.5 nm, and a channel length ranging from 80 nm to 1 μm demonstrate markedly improved electrical performances, including a high field effect mobility of 72.8 cm2/V s, a more positive threshold voltage, a higher on/off current ratio of ∼106, a smaller subthreshold swing below 200 mV/dec, and a higher stability to both negative and positive gate biases. X-ray photoelectron spectroscopy (XPS) confirms the fluorine incorporation in In2O3/HfO2 heterojunction upon CF4/N2O plasma, speculatively passivating the oxygen vacancies and explaining TFT performance enhancement. This study suggests that the anion doping such as fluorine incorporation could be an effective method to improve the performance of oxide semiconductor TFTs with ultrathin channel and dielectric. [ABSTRACT FROM AUTHOR]

High-pressure hydrogen annealing (HPHA) treatment is an effective hydrogen doping method to improve electrical characteristics and stability of InGaZnO (IGZO) thin film transistors (TFTs). The HPHA effects on IGZO TFTs under various pressure conditions were investigated using analytical techniques. Drive current, field effect mobility, subthreshold swing, and bias stress stability of IGZO TFTs were significantly improved as the HPHA pressure was increased up to 20 atm. To analyze the performance enhancement, secondary ion mass spectroscopy, capacitance–voltage analysis, and x-ray photoelectron spectroscopy analysis techniques were performed. As a result, it was confirmed that doped hydrogen is combined with interface trap sites and oxygen vacancy related bulk defect sites, leading to improved subthreshold swing and bias stress stability. Furthermore, bulk trap passivation also contributes to high carrier density, thereby increasing driving current and field effect mobility. With increasing HPHA pressure condition, these effects of trap passivation and increase in the carrier density are more effective due to the heavily injected hydrogen. [ABSTRACT FROM AUTHOR]

Ferroelectric devices have wide applications in nonvolatile random-access memories, sensors, actuators, and transducers. The built-in potential at the interfaces could result in poor polarization retention. Here, we found an effective way to independently adjust two coercive fields of LiNbO3 mesa-like domain wall devices in contact to two side electrodes at the surface. Taking advantage of the electrode shielding effect on the depolarization field across an interfacial layer, the near-zero coercive field increases almost linearly with respect to the extending length of one side electrode covering the tail of the reversed domain, enabling nonvolatile ferroelectric domain wall devices in good polarization retention and fast operation speeds. [ABSTRACT FROM AUTHOR]

Electrically detected magnetic resonance (EDMR) measurements have been extended to sub-mT magnetic fields through utilization of frequency sweeping of the oscillating magnetic field, where conventional electron paramagnetic resonance-based measurements traditionally utilize magnetic field magnitude ramping. In spin-dependent transport measurements in devices, an oftentimes pervasive near-zero field magnetoresistance effect overwhelms the sub-mT regime. This magnetoresistance effect is independent of the RF drive. Thus, by utilizing a constant DC magnetic field and a frequency sweep of the RF magnetic field, the magnetoresistance effect is not detected, leaving only the EDMR response. Interesting EDMR-based phenomena emerge at sub-mT fields when the oscillating field magnitude approaches the static field, such as multiple-photon transitions caused by the emergence of Floquet spin states and Bloch–Siegert shifts. A spectral-narrowing effect also emerges as the static field is reduced. In this work, we show that the narrowing of the frequency-swept EDMR response with static field can be modeled by changes in intermediate spin-pair relaxation through modulation of hyperfine fields caused by stochastic perturbations from the environment. We utilize recently developed theory to model the relaxation of spin pairs and show that stochastic interactions of the electron spin with the environment yield both Floquet spin states and changes in intermediate spin-pair relaxation. [ABSTRACT FROM AUTHOR]

In this work, a transparent and free-standing ionic gel as the dielectric layer for polarization switching in leaky ferroelectric thin films is reported. By applying an electric field over an ionic liquid dielectric layer used as an electrostatic field gated capacitor, one can avoid electronic conduction. The association of the electrical double layer with depolarization at the solid–liquid interface contributes to the reversible switching in PbZrxTi1−xO3 (x = 0.6) (PZT). Using such ionic gels, the anisotropic ferroelastic switching from mono-c-domain toward a-domain is studied in PZT grown on CaF2 substrates. Our results demonstrate that an electrostatic field, induced by the free-standing ionic gel, is an effective and promising way to investigate leaky ferroelectrics. [ABSTRACT FROM AUTHOR]

Electric-field controlled magnetism is a potential way to realize strong magneto-electric (ME) coupling for nonvolatile memory applications. The electric field induced nonvolatile modulated magnetization was obtained in NiFe2O4/SrRuO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) thin film heterostructures. The collective effect of charge and strain significantly modified the magnetization of the NiFe2O4 layer in NiFe2O4/SrRuO3/PMN-PT heterostructures. The analysis of XMCD data establishes that the cation (Fe3+/Ni2+) redistribution occurs on tetrahedral and octahedral sites in the electric field poled NiFe2O4 films, confirming the coupling between magnetism and ferroelectric properties. The films demonstrate repeatable switching of sign of ME output voltage α (α = dP/dH) in response to the applied positive and negative electric pulse, which can be used to store binary information in the nonvolatile manner. The electric-field-controlled switching of α in thin films offers an energy-efficient approach for low-power-consumption nonvolatile memory devices. [ABSTRACT FROM AUTHOR]

We present an analysis of the optical coupling between two gold nanodisks by near-field fluorescence microscopy. This is achieved by simultaneously scanning and measuring the light emitted by a single Er3+/Yb3+ doped nanocrystal glued at the end of an atomic force microscope tip. The excitation of the nanocrystal was performed at λ = 975 nm via upconversion, and fluorescence was detected in the visible part of the spectrum at λ = 550 nm. For an isolated nanodisk, the near-field presents a two-lobe pattern oriented along the direction of the incident polarization. For two nanodisks with a sizable separation distance (385 nm) illuminated with the polarization along the interparticle axis, we observe a negative effect of the coupling with a slight decrease in fluorescence in the gap. For smaller gap values (195, 95, and 55 nm), a strong increase in fluorescence is observed as well as a reduced spatial localization of the field as the distance decreases. Finally, when the disks touch each other (0 nm), the dipolar–dipolar interaction between them disappears and no fluorescence enhancement occurs. A new plasmon mode is created at another wavelength. Our experimental results are in good agreement with numerical simulations of the near-field intensity distribution at the excitation wavelength on the surface of the structures. Combining fluorescence mapping and far-field scattering spectroscopy should be of strong interest to develop bio-chemical sensors based on field enhancement effects. [ABSTRACT FROM AUTHOR]

We study how the collective effects of nanoparticles arranged in rectangular arrays influence their temporal plasmon response and field enhancement property. By systematically changing the lattice constant for arrays containing identical metal nanorods, we experimentally demonstrate how grating-induced effects affect the position and, more importantly, the broadening of extinction spectra. We correlate these effects with the achievable field enhancement and the temporal duration of plasmon transients and formulate criteria for the generation of enhanced few-cycle localized plasmon oscillations. [ABSTRACT FROM AUTHOR]

We have developed an approach to control the carrier density in various materials under high pressure by the combination of an electric double layer transistor (EDLT) and a diamond anvil cell (DAC). In this study, this "EDLT-DAC" was applied to a Bi thin film, and here, we report the field effect under high pressure in the material. Our EDLT-DAC is a promising device for exploring unknown physical phenomena such as high transition-temperature superconductivity. [ABSTRACT FROM AUTHOR]

One of the main advantages of Ion-Sensitive Field-Effect Transistor (ISFET) technology is the capability to exploit technological advancements initially developed for conventional FETs for logic applications, such as the employ of high-k dielectrics for the gate and the definition of fully depleted and gate all around structures. Negative Capacitance (NC) is an emerging concept exploiting ferroelectric materials integrated in field effect transistor gate stacks in order to decrease their subthreshold swing and improve the drain current (ID) overdrive in order to reach more energy efficient devices, operated at lower voltage. In this work, we investigate and experimentally demonstrate the application of this concept to enable subthermionic ISFETs with enhanced current sensitivity and low power operation. A physical model for the introduced NC ISFET is presented and optimized by fitting of the experimental results, providing further insights into the sensor parameters and a predictive tool for the design of future NC-based sensors. [ABSTRACT FROM AUTHOR]

Interfaces between two topological insulators are of fundamental interest in condensed matter physics. Inspired by experimental efforts, we study interfacial processes between two slabs of BiSbTeSe 2 (BSTS) via first principles calculations. Topological surface states are absent for the BSTS interface in its equilibrium separation, but our calculations show that they appear if the inter-slab distance is greater than 6 Å. More importantly, we find that topological interface states can be preserved by inserting two or more layers of hexagonal boron nitride between the two BSTS slabs. In experiments, the electric current tunneling through the interface is insensitive to back gate voltage when the bias voltage is small. Using a first-principles based method that allows us to simulate the gate field, we show that at low bias, the extra charge induced by a gate voltage resides on the surface that is closest to the gate electrode, leaving the interface almost undoped. This provides clues to understand the origin of the observed insensitivity of transport properties to back voltage at low bias. Our study resolves a few questions raised in experiment, which does not yet offer a clear correlation between microscopic physics and transport data. We provide a road map for the design of vertical tunneling junctions involving the interface between two topological insulators. [ABSTRACT FROM AUTHOR]

We report experimental results on the low-frequency noise in GaN/AlGaN transistors fabricated under different conditions and evaluate different methods to extract the effective trap density using the McWhorter model. The effective trap density is found to be below 1019 cm−3 for some of the wafers. This trap density is of the same order of magnitude as that reported in Si MOSFETs with a high-k dielectric. One of the structures manifested about two orders of magnitude higher noise level. These measurements correlate with the results of secondary ion mass spectroscopy and terahertz electroluminescence measurements which indicated a ∼30% higher concentration of uncompensated oxygen in this structure. Effective trap density extracted from noise measurements is proven to be a very sensitive figure of merit parameter for the GaN/AlGaN field effect transistors and material quality assessment. [ABSTRACT FROM AUTHOR]

A high activation ratio of acceptors to Mg ions implanted into a homoepitaxial GaN layer was achieved through an ultra-high-pressure annealing (UHPA) process. Capless annealing under a nitrogen pressure of 1 GPa in a temperature range of 1573–1753 K activated acceptors without thermally decomposing the GaN layer. Conventional rapid thermal annealing leads to a serious decomposition at 1573 K, even with an AlN protective cap. The sample annealed at 1673 K under UHPA exhibited very intense cathodoluminescence in near-band edge and donor-acceptor-pair band emissions. The intensities were over one order of magnitude higher than those of the sample treated by conventional annealing. A Hall-effect measurement was obtained in the temperature range of 275–500 K for the UHPA sample. The obtained hole concentration and mobility at 300 K were 3.6 × 1016 cm−3 and 24.1 cm2 V−1 s−1, respectively. The mobility value was close to that of an epitaxial p-type GaN with the same doping concentration. An Arrhenius plot of hole concentrations showed that the acceptor concentration and ionization energy were separately estimated to be (2.6 ± 0.8) × 1018 cm−3 and 212 ± 5 meV, respectively. By comparing the Mg concentrations obtained from secondary ion mass spectrometry, the acceptor activation ratio (acceptor concentration/Mg concentration) of the UHPA samples exceeded 70%. These results suggest that the UHPA process as a postimplantation annealing technique is promising for the fabrication of GaN-based power devices with selective area doping. [ABSTRACT FROM AUTHOR]

Skyrmions have become one of the most visited topics during the last decade in condensed matter physics. In this work, and by means of analytical calculations and micromagnetic simulations, we explore the effect of the magnetostatic field generated by a magnetic tip on the stability of skyrmions. Our results show that the interaction energy between the tip and the skyrmion plays a fundamental role in the stabilization of Néel skyrmions confined in nanodisks, allowing its nucleation and annihilation and also providing precise control of its size and polarity. Based on our results, we propose a very simple and cyclic method to nucleate and annihilate skyrmions, as well as to control their polarity and chirality. This proposal could open possibilities for logic devices taking advantage of all the degrees of freedom that skyrmionic textures have. [ABSTRACT FROM AUTHOR]

FeSn is a room-temperature antiferromagnet expected to host Dirac fermions in its electronic structure. The interplay of the magnetic degree of freedom and the Dirac fermions makes FeSn an attractive platform for spintronics and electronic devices. While stabilization of thin film FeSn is needed for the development of such devices, there exist no previous reports of epitaxial growth of single crystalline FeSn. Here, we report the realization of epitaxial thin films of FeSn (001) grown by molecular beam epitaxy on single crystal SrTiO3 (111) substrates. By combining X-ray diffraction, electrical transport, and torque magnetometry measurements, we demonstrate the high quality of these films with the residual resistivity ratio ρ xx (300 K) / ρ xx (2 K) = 24 and antiferromagnetic ordering at T N = 353 K. These developments open a pathway to manipulate the Dirac fermions in FeSn by both magnetic interactions and the electronic field effect for use in antiferromagnetic spintronics devices. [ABSTRACT FROM AUTHOR]

We propose a hybrid scheme that smoothly interpolates the Ziegler-Biersack-Littmark (ZBL) screened nuclear repulsion potential with a deep learning potential energy model. The resulting deep potential-ZBL model can not only provide overall good performance on the predictions of near-equilibrium material properties but also capture the right physics when atoms are extremely close to each other, an event that frequently happens in computational simulations of irradiation damage events. We applied this scheme to the simulation of the irradiation damage processes in the face-centered-cubic aluminum system and found better descriptions in terms of the defect formation energy, evolution of collision cascades, displacement threshold energy, and residual point defects than the widely adopted ZBL modified embedded atom method potentials and their variants. Our work provides a reliable and feasible scheme to accurately simulate the irradiation damage processes and opens up extra opportunities to solve the predicament of lacking accurate potentials for enormous recently discovered materials in the irradiation effect field. [ABSTRACT FROM AUTHOR]

The detection of biomolecules by a Field Effect Transistor-based biosensor (BioFET) is dictated by the sensor's intrinsic Signal-to-Noise Ratio (SNR). The detection limit of a traditional BioFET is fundamentally limited by biomolecule diffusion, charge screening, linear charge to surface-potential transduction, and Flicker noise. In this letter, we show that the recently introduced class of transistors called negative capacitor field effect transistors offers nonlinear charge transduction and suppression of Flicker noise to dramatically improve the SNR over classical Boltzmann sensors. We quantify the SNR improvement (approximately two orders of magnitude higher than a classical Si-nanowire biosensor) by interpreting the experimental results associated with the signal and noise characteristics of 2D MoS2-based transistors. The proposed Negative Capacitor BioFET (NC-BioFET) will motivate experimentalists to combine two well-established technologies to achieve high SNR (and to improve the detection limit), fundamentally unachievable by any other sensor technology. [ABSTRACT FROM AUTHOR]

Oxide heterostructures are an attractive platform for incorporation in field-effect transistors (FETs) due to their diverse physical properties which can be tuned by electrostatic gating. We report a top-gated FET based on a SrTiO3 delta-doped structure, which operates down to cryogenic temperatures. The device shows excellent DC characteristics with an on/off ratio greater than 104 and field effect mobility estimated to be 2125 cm2/V s at 2 K. The high field effect mobility was consistent with the Hall mobility and is attributed to the formation of a two-dimensional electron system in the delta-doped layer: two-dimensional gate-tunable Shubnikov-de Haas oscillations confirm this. The achievement of an electron density of 3 × 1012 cm−2 in a gate-tunable geometry allows for the exploration of the interplay between magnetic, ferroelectric, and superconducting properties of SrTiO3 in the quantum limit. [ABSTRACT FROM AUTHOR]

We have manufactured oxide field-effect transistors using the electron system at the LaAlO3-SrTiO3 interface as a drain-source channel and measured the devices under a hydrostatic pressure of up to 1.8 GPa. These studies of oxide transistors in the high-pressure regime demonstrate remarkable stability of the devices against gate leakage and resilience to mechanical strain. They show that oxide transistors can be operated in a wide range of pressures and temperatures and open the road for future studies of oxide materials and their possible applications in electronics. [ABSTRACT FROM AUTHOR]

Ultrathin amorphous ZnSnO (a-ZTO) films and ultrathin amorphous ZnGeSnO (a-ZGTO) films with various Ge contents were deposited by pulsed laser deposition for ultra-thin-film transistors (UTFTs). The thicknesses of the channel layers are approximately 3.2 nm. The properties of these ultrathin films and behaviors of these UTFTs were comparatively studied in detail. The a-ZTO ultrathin film exhibited a low concentration of the oxygen vacancy (VO) compared to a-ZGTO ultrathin films. Among all the UTFTs, the a-ZTO UTFT demonstrated the undoubtedly best performance with an on/off current ratio of more than 107, the largest field-effect mobility of 23.2 cm2 V−1 s−1, a positive threshold voltage of 2.0 V, a very small subthreshold swing of 0.31 V/decade, and the best long-term stability under bias stress, suggesting that the introduction of VO suppressors is dispensable with such a small thickness. Above all, the concentration of the oxygen vacancy is easily controlled in the ultrathin a-ZTO nanofilms, leading to the UTFTs operating in the enhancement mode with a high field-effect mobility of 23.2 cm2 V−1 s−1 and excellent long-term stability. The a-ZTO ultrathin film and ultra-thin-film transistor are very potential for future electrical applications with their excellent properties. [ABSTRACT FROM AUTHOR]

Reverse bias leakage in bulk GaN-on-GaN pn diodes has been studied as a function of time. A peak was observed in the current transient and attributed to impurity band conduction along dislocations which is modulated by the field effect of charged decorating clusters. This model is consistent with reports of vacancy clustering around dislocations during growth. [ABSTRACT FROM AUTHOR]

The effects of oxygen incorporation on the electronic transport properties of two-dimensional (2D) MoS2 have been studied via temperature dependent and gate voltage dependent transport measurements of physical vapor deposited 2D MoS2. Gated micro-van der Pauw cross devices were fabricated from the MoS2 film for transport measurements. Field-effect measurements indicate that incorporated oxygen acts as a p-type dopant for MoS2. The combination of X-ray photoemission spectroscopy surface analysis and Raman measurements of the film indicates that acceptor states resulting from MoSxO3-x inclusions in the MoS2 film are the origin of the p-type doping. Temperature dependent van der Pauw conductivity measurements indicate an acceptor energy of 214 meV above the valence band edge for the acceptor state. [ABSTRACT FROM AUTHOR]

We report an interband tunneling field effect transistor (TFET) integrated with a Black Phosphorus (BP)-MoS2 junction and ion gel as a top gate dielectric. The operation of the BP-MOS2 TFET is based on the modulation of the energy band alignment of the BP-MoS2 junction with electrostatic gating control on the MoS2 channel from the top gate through the ion gel dielectric and the supply of tunneling carriers from the BP source, which is degenerately doped with ion gel. The obtained subthreshold swing of the BP-MoS2 TFET reached 65 mV/dec at room temperature and 51 mV/dec at 160K, maintaining low SS values in more than 2 orders of drain current range. The demonstrated interband TFET based on the BP-MoS2 junction shows significant promise for further application to a new class of two-dimensional functional devices. [ABSTRACT FROM AUTHOR]

We use first-principles calculations to investigate the interplay between strain and the charge state of point defect impurities in complex oxides. Our work is motivated by recent interest in using defects as active elements to provide novel functionality in coherent epitaxial films. Using oxygen vacancies as model point defects, and CaMnO3 and MnO as model materials, we calculate the changes in internal strain caused by changing the charge state of the vacancies, and conversely the effect of strain on charge-state stability. Our results show that the charge state is a degree of freedom that can be used to control the interaction of defects with strain and hence the concentration and location of defects in epitaxial films. We propose the use of field-effect gating to reversibly change the charge state of defects and hence the internal strain and corresponding strain-induced functionalities. [ABSTRACT FROM AUTHOR]

Ferroelectric field-effect transistors (FeFET) based on MoS2 have recently been shown to exhibit considerable potential for use in nano sized non-volatile memory devices. Here, we demonstrated fabrication and characterization of FeFET based on MoS2 channel with vinylidene fluoride (VDF)-trifluoroethylene (TrFE) copolymer as back-gate insulator. In this device, counterclockwise hysteresis behavior was observed in the drain current-gate voltage curve, which is indicative of interaction between MoS2 carrier modulation and ferroelectric polarization switching. Furthermore, our VDFTrFE/MoS2 FeFET exhibited only n-type behavior, a maximum linear mobility of 625 cm2/V s, a large memory window width of 16 V, and a high on/off current ratio of 8 × 105. [ABSTRACT FROM AUTHOR]

A stretchable and pressure sensitive polymer capable of detecting strains was developed through the incorporation of 1-ethyl-3-methylimidazolium tetrafluoroborate as an ionic liquid (IL) into a stretchable photopolymer. The developed IL/polymer composite showed both a field effect characteristic and piezoresistivity by embedding the composite between two layers of carbon nanotube (CNT)-based stretchable electrodes. A multi-layer pressure sensitive taxel was formed using a hybrid manufacturing process, where two electrode layers were fabricated by screen printing and the IL/polymer composite was formed by casting using a mold. A composite material for the electrodes was developed through the dispersion of CNTs into a highly stretchable photo/thermal crosslinkable prepolymer. The fabricated sensor was evaluated with different forces ranging from 0 to 140 g. The experiment results showed that the developed stretchable sensor had good repeatability and reliability in detecting applied pressures. [ABSTRACT FROM AUTHOR]

We report the effect of epitaxial strain on the magnitude and retention of the ferroelectric field effect in high quality PbZr0.3Ti0.7O3 (PZT)/3.8-4.3 nm Sm0.5Nd0.5NiO3 (SNNO) heterostructures grown on (001) LaAlO3 (LAO) and SrTiO3 (STO) substrates. For SNNO on LAO, which exhibits a first-order metal-insulator transition (MIT), switching the polarization of PZT induces a 10K shift in the transition temperature TMI, with a maximum resistance change between the on and off states of ΔR=Ron ~75%. In sharp contrast, only up to 5% resistance change has been induced in SNNO on STO, where the MIT is second-order, with the modulation of TMI negligibly small. We also observe thermally activated retention of the off state resistance Roff in both systems, with the activation energy of 22 meV (28 meV) for devices on LAO (STO). The time dynamics and thermal response of the field effect instability points to phonon-assisted interfacial trapping of charged mobile defects, which are attributed to strain induced oxygen vacancies. At room temperature, Roff stabilizes at ~55% and ~19% of the initial switching levels for SNNO on LAO and STO, respectively, reflecting the significantly different oxygen vacancy densities in these two systems. Our results reveal the critical role of strain in engineering and modeling the complex oxide composite structures for nanoelectronic and spintronic applications. [ABSTRACT FROM AUTHOR]

We report the effect of epitaxial strain on the magnitude and retention of the ferroelectric field effect in high quality PbZr0.3Ti0.7O3 (PZT)/3.8-4.3 nm Sm0.5Nd0.5NiO3 (SNNO) heterostructures grown on (001) LaAlO3 (LAO) and SrTiO3 (STO) substrates. For SNNO on LAO, which exhibits a first-order metal-insulator transition (MIT), switching the polarization of PZT induces a 10K shift in the transition temperature TMI, with a maximum resistance change between the on and off states of ΔR=Ron ~75%. In sharp contrast, only up to 5% resistance change has been induced in SNNO on STO, where the MIT is second-order, with the modulation of TMI negligibly small. We also observe thermally activated retention of the off state resistance Roff in both systems, with the activation energy of 22 meV (28 meV) for devices on LAO (STO). The time dynamics and thermal response of the field effect instability points to phonon-assisted interfacial trapping of charged mobile defects, which are attributed to strain induced oxygen vacancies. At room temperature, Roff stabilizes at ~55% and ~19% of the initial switching levels for SNNO on LAO and STO, respectively, reflecting the significantly different oxygen vacancy densities in these two systems. Our results reveal the critical role of strain in engineering and modeling the complex oxide composite structures for nanoelectronic and spintronic applications. [ABSTRACT FROM AUTHOR]

A delay-line detector is established for electron detection in the field of scanning transmission electron microscopy (STEM) and applied to two-dimensional strain mapping in Si-based field effect transistors. We initially outline the functional principle of position-sensitive delay-line detection, based on highly accurate time measurements for electronic pulses travelling in meandering wires. In particular, the detector is a single-counting device essentially providing an infinite time stream of position-resolved events so that acquisition speed is not hindered by detector read-outs occurring in conventional charge-coupled devices. By scanning the STEM probe over stressor- and gate regions of a field effect transistor on a 100×100 raster, 10 000 diffraction patterns have been acquired within 3-6.5 min, depending on the scan speed. Evaluation of the 004 and 220 reflections yields lateral and vertical strain at a spatial resolution of 1.6 nm. Dose-dependent strain precisions of 1:2 - 1:8 × 10-3 could be achieved for frame times of 40 and 20 ms, respectively. Finally, the detector is characterised as to quantum efficiency and further scopes of application are outlined. [ABSTRACT FROM AUTHOR]

Contact resistance has great impact on the performance of oxide thin film transistors (TFTs) and their applications. In this letter, temperature, gate voltage, and electrode dependences of the contact resistance were investigated in amorphous InGaZnO (a-IGZO) TFTs. We found that gate voltage dependent contact resistance made a large contribution to or even dominated the "field effect" of oxide TFTs. After separating the influence of contact resistance, the intrinsic temperature dependent field effect mobility of the a-IGZO TFTs was obtained. Furthermore, the experimental data of the contact resistance can be well described by an optimized transmission line model, and the height of the Schottky barrier in the interface between the metal electrode and a-IGZO semiconductor was found to be related to the gate voltage and account for the contact resistance's dependence on the gate voltage. [ABSTRACT FROM AUTHOR]

We report a large enhancement of the Hall mobility of a ZnO film (channel) by simultaneously application of an ultraviolet illumination along with a gate bias in an electric double layer field effect transistor configuration. The effect arises from a synergy between the illumination and the field effect (FE), leading to large enhancement of the channel conductivity and the photo response. We propose that large carrier density created by the simultaneous presence of the illumination and the FE leads to neutralization of some of the oxygen charged vacancies which in turn reduce potential scattering leading to the enhanced mobility. [ABSTRACT FROM AUTHOR]

The effect of the symmetries in the terahertz (THz) field distribution and the field-effect channel on THz photoresponse is examined. Resonant excitation of cavity plasmon modes and nonresonant self-mixing of THz waves are demonstrated in a GaN/AlGaN two-dimensional electron gas with symmetrically designed nanogates, antennas, and filters. We found that the self-mixing signal can be effectively suppressed by the symmetric design and the resonant response benefits from the residual asymmetry. The findings suggest that a single detector may provide both high sensitivity from the self-mixing mechanism and spectral resolution from the resonant response by optimizing the degree of geometrical and/or electronic symmetries. [ABSTRACT FROM AUTHOR]

In this study, we proposed the artificially designed channel structure in oxide thin-film transistors (TFTs) called a "step-composition gradient channel." We demonstrated Al step-composition gradient Al-Zn-O (AZO) channel structures consisting of three AZO layers with different Al contents. The effects of stacking sequence in the step-composition gradient channel on performance and electrical stability of bottom-gate TFT devices were investigated with two channels of inverse stacking order (ascending/descending step-composition). The TFT with ascending step-composition channel structure (5 → 10 → 14 at.% Al composition) showed relatively negative threshold voltage (-3.7 V) and good instability characteristics with a reduced threshold voltage shift (Δ1.4V), which was related to the alignment of the conduction band off-set within the channel layer depending on the Al contents. Finally, the reduced Al composition in the initial layer of ascending step-composition channel resulted in the best field effect mobility of 4.5cm²/V s. We presented a unique active layer of the "step-composition gradient channel" in the oxide TFTs and explained the mechanism of adequate channel design. [ABSTRACT FROM AUTHOR]

Device performance of InGaZnO (IGZO) thin film transistors (TFTs) are investigated as a function of hydrogen ion irradiation dose at room temperature. Field effect mobility is enhanced, and subthreshold gate swing is improved with the increase of hydrogen ion irradiation dose, and there is no thermal annealing. The electrical device performance is correlated with the electronic structure of IGZO films, such as chemical bonding states, features of the conduction band, and band edge states below the conduction band. The decrease of oxygen deficient bonding and the changes in electronic structure of the conduction band leads to the improvement of device performance in IGZO TFT with an increase of the hydrogen ion irradiation dose. [ABSTRACT FROM AUTHOR]

Extrinsic hysteresis effects are often observed in MoS2 field effect devices due to adsorption of gas molecules on the surface of MoS2 channel. Scaling is a common method used in ferroics to quantitatively study the hysteresis. Here, the scaling behavior of hysteresis in multilayer MoS2 field effect transistors with a back-gated configuration was investigated. The power-law scaling relations were obtained for hysteresis area () and memory window (ΔV) with varying the region of back-gate voltage (Vbg,max). It is interesting to find that the transition voltage in the forward sweep (VFW) and in the backward sweep (VBW) shifted to the opposite directions of back-gate voltage (Vbg) with increasing Vbg,max. However, when decreasing Vbg,max, VFW shifted to positive and reversibly recovered, but VBW almost kept unchanged. The evolution of , ΔV, VFW, and VBW with Vbg,max were discussed by the electrons transferring process between the adsorbate and MoS2 channel. [ABSTRACT FROM AUTHOR]

We investigate the correlation between the atomic structures of amorphous zinc-tin-oxide (a-ZTO) thin films grown by atomic layer deposition (ALD) and their electronic transport properties. We perform synchrotron-based X-ray absorption spectroscopy at the K-edges of Zn and Sn with varying [Zn]/[Sn] compositions in a-ZTO thin films. In extended X-ray absorption fine structure (EXAFS) measurements, signal attenuation from higher-order shells confirms the amorphous structure of a-ZTO thin films. Both quantitative EXAFS modeling and X-ray absorption near edge spectroscopy (XANES) reveal that structural disorder around Zn atoms increases with increasing [Sn]. Field- and Hall-effect mobilities are observed to decrease with increasing structural disorder around Zn atoms, suggesting that the degradation in electron mobility may be correlated with structural changes. [ABSTRACT FROM AUTHOR]

We validate the linear dispersion relation (Dirac cone) on the surface of a single Bi2Te3 nanowire via a combination of field-effect and magnetoresistance measurements by which we unambiguously prove the topological insulator nature of the nanowire surface states. Moreover, we show that the experimentally determined carrier concentration, mobility, and cyclotron mass of the surface states are in excellent agreement with relativistic models. Our method provides a facile way to identify topological insulators that too small for angle-resolved photoemission spectroscopy. [ABSTRACT FROM AUTHOR]

The recombination of electric charge carriers at the surface of semiconductors is a major limiting factor in the efficiency of optoelectronic devices, in particular, solar cells. The reduction of such recombination, commonly referred to as surface passivation, is achieved by the combined effect of a reduction in the trap states present at the surface via a chemical component, and the reduction in the charge carriers available for a recombination process, via a field effect component. Here, we propose a technique to field effect passivate silicon surfaces using the electric field effect provided by alkali ions present in a capping oxide. This technique is shown to reduce surface recombination in a controlled manner, and to be highly stable. Surface recombination velocities in the range of 6-15 cm/s are demonstrated for 1 Ω cm n-type float zone silicon using this technique, and they are observed to be constant for over 300 days, without the use of any additional surface chemical treatment. A model of trapping-mediated ionic injection is used to describe the system, and activation energies of 1.8-2 eV are deduced for de-trapping of sodium and potassium alkali ionic species. [ABSTRACT FROM AUTHOR]

Indium Arsenide is a high mobility semiconductor with a surface electron accumulation layer that allows ohmic electrical contact to metals. Here, we present nanowire devices based on this material as a platform for chemical and biological sensing. The sensing principle involves the binding of a charged species at the sensor surface transduced via field effect into a change in current flowing through the sensor. We show the sensitivity of the platform to the H+ ion concentration in solution as proof of principle and demonstrate the sensitivity to larger charged protein species. The sensors are highly reproducible and reach a detection limit of 10 pM for Avidin. [ABSTRACT FROM AUTHOR]

In this article, an expression for the surface passivation has been derived in terms of the surface recombination velocity and the field-effect exponential. The analytical solutions provide a comprehensive understanding of the injection dependency of minority charge carrier lifetime as measured by photoconductance decay. The model has been utilized to analyze the field-effect passivation of silicon exerted by the fixed dielectric charge in an overlying dielectric film. Possible limitations and restrictions of the technique are also addressed. [ABSTRACT FROM AUTHOR]

Tuning of the Fermi level is investigated in graphene channels using two in-plane gates with significantly different-sized isolating gaps. While the n-type tuning was achievable in both schemes, the wide-gap device had an enhanced minimum drain current and less prominent current modulation than the narrow-gap device. In addition, further p-type tuning was not observed in the wide-gap device at negative gate biases. These phenomena indicated that both devices had distinct field-strength dependences and Fermi level tuning effects, which may be critical for the practical design of devices. [ABSTRACT FROM AUTHOR]

We report bilayer-graphene field effect transistors operating as Terahertz (THz) broadband photodetectors based on plasma-waves excitation. By employing wide-gate geometries or buried gate configurations, we achieve a responsivity ~1.2 V/W (1.3 mA/W) and a noise equivalent power ~2×10-9 W/√Hz in the 0.29-0.38 THz range, in photovoltage and photocurrent mode. The potential of this technology for scalability to higher frequencies and the development of flexible devices makes our approach competitive for a future generation of THz detection systems. [ABSTRACT FROM AUTHOR]