Showing papers on "Field effect published in 2020"

Orthogonal Electric Control of the Out-Of-Plane Field-Effect in 2D Ferroelectric α-In2Se3

Abstract: DOI: 10.1002/aelm.202000061 scheme is constructing the device referred to as field-effect transistor (FET), in which an external voltage can be applied to vary the carrier doping of the material in the conducting channel. To date, there have been delivered several types of FETs.[5,7,10–14] Subject to specific gate dielectric, the FETs function in distinctive way, including electrostatically accumulation of carriers via oxide insulator or ferroelectrics,[12–14] forming the electric double layer of large capacitance by organic ionic liquids,[10,11,15] and driving ion intercalation from recently developed solid ionic gel or conductor.[5,7] However, limited by the linear electric response of conventional gate dielectrics, the device geometry in most field-effect studies is fixed to be capacitor-like by placing an indispensable gate electrode either on top or at bottom to sandwich the dielectrics. The field-effect is therefore induced by the gate electric field, which is always perpendicular to the conducting channel. This stereo structure geometry consequently increases the device complexity and furtherly limits its application in specific areas only. To that end, FETs with new conceptual design is highly desired, especially for developing flexible nano electronics and optoelectronics with van der Waals (vdW) materials. In this work, to overcome the limitation, we present a new approach to create a vertical field-effect in a coplanar device with layered α-In2Se3 as the gate dielectric. α-In2Se3 is an emerging 2D ferroelectric semiconductor with remarkable optical and transport properties.[16–19] Recent studies have confirmed its stable room-temperature ferroelectricity at the single atomic layer limit with the unique intercorrelation of out-of-plane and in-plane electric polarizations.[20–26] For ferroelectrics, especially when forming heterostructures, their polarity is an effective knob to tune the electrostatic doping as well as the global electronic structure, resulting practical device potential such as ferroelectric field-effect transistors (FeFETs).[27] This same scenario is applicable to all 2D ferroelectrics with OOP electric polarizations.[13,28,29] In additional to the OOP ferroelectricity, α-In2Se3 presents the unique inter-locking feature of electric dipoles. The flipping of the IP electric polarization in α-In2Se3 can be achieved by an OOP bias,[21,24] or vice versa. Therefore, it suggests that one can develop coplanar FET (CP-FET) with ultrathin α-In2Se3, where the out-of-plane (OOP) electric gating effect is controlled by an in-plane (IP) voltage. Our results are summarized in the following. We verify that the IP and OOP electric polarization in 3R α-In2Se3 thin Tuning the electric properties of crystalline solids is at the heart of material science and electronics. Generating the electric field-effect via an external voltage is a clean, continuous, and systematic method. Here, utilizing the unique electric dipole locking in van der Waals (vdW) ferroelectric α-In2Se3, a new approach is reported to establish the electric gating effect, where the electrostatic doping in the out-of-plane direction is induced and controlled by an in-plane voltage. With the vertical vdW heterostructure of ultrathin α-In2Se3 and MoS2, an in-plane voltage gated coplanar field-effect transistor with distinguished and retentive on/off ratio is validated. The results demonstrate unprecedented electric control of ferroelectricity, which paves the way for integrating 2D ferroelectric into novel nanoelectronic devices with broad applications.

Electric field control of disorder-tunable superconductivity and the emergence of quantum metal at an oxide interface

Abstract: We report on an extraordinary field effect of the superconducting LaAlO3/KTaO3(111) interface with Tc ~2 K. By applying a gate voltage (VG) across KTaO3, the interface can be continuously tuned from superconducting into insulating states, yielding a dome-shaped Tc-VG dependence. The electric gating has only a minor effect on carrier density as evidenced in the Hall-effect measurement, while it changes spatial profile of the carriers in the interface, hence the carrier's disorder level significantly. As temperature is decreased, the resistance saturates at lowest temperature in both superconducting and insulating sides, despite an initial dramatic dropping or increasing, which suggests an emergence of quantum metallic state associated with failed superconductor and/or fragile insulator. A VG-modulation of the magnetic-field-driven superconductor to insulator quantum phase transition reveals a non-universal criticality.

Tuning Electrical Conductance in Bilayer MoS2 through Defect-Mediated Interlayer Chemical Bonding

Abstract: Interlayer interaction could substantially affect the electrical transport in transition metal dichalcogenides, serving as an effective way to control the device performance. However, it is still challenging to utilize interlayer interaction in weakly interlayer-coupled materials such as pristine MoS2 to realize layer-dependent tunable transport behavior. Here, we demonstrate that, by substitutional doping of vanadium atoms in the Mo sites of the MoS2 lattice, the vanadium-doped monolayer MoS2 device exhibits an ambipolar field effect characteristic, while its bilayer device demonstrates a heavy p-type field effect feature, in sharp contrast to the pristine monolayer and bilayer MoS2 devices, both of which show similar n-type electrical transport behaviors. Moreover, the electrical conductance of the doped bilayer MoS2 device is drastically enhanced with respect to that of the doped monolayer MoS2 device. Employing first-principle calculations, we reveal that such striking behaviors arise from the presence of electrical transport networks associated with the enhanced interlayer hybridization of S-3pz orbitals between adjacent layers activated by vanadium dopants in the bilayer MoS2, which is nevertheless absent in its monolayer counterpart. Our work highlights that the effect of dopant not only is confined in the in-plane electrical transport behavior but also could be used to activate out-of-plane interaction between adjacent layers in tailoring the electrical transport of the bilayer transitional metal dichalcogenides, which may bring different applications in electronic and optoelectronic devices.

Comprehensive Review on Amorphous Oxide Semiconductor Thin Film Transistor

Abstract: Oxide materials are one of the most advanced key technology in the thin film transistors (TFTs) for the high-end of device applications. Amorphous oxide semiconductors (AOSs) have leading technique for flat panel display, active matrix organic light emitting display, active matrix liquid crystal display as well as thin film electronic devices due to their excellent electrical characteristics, such as field effect mobility (μFE), subthreshold swing (SS) and threshold voltage (Vth). Researchers from various fields have studied and considered ways to improve µFE of AOS TFT, which has been studied for 16 years since 2004. Since 2004, mobility has been increased by using various methods, such as designing novel amorphous oxide materials, changing device structures, or adopting new post-treatment. The development of field effect mobility as well as the stability enhancement has been comprehensively reviewed in this report.

Electric Fields at Metal-Surfactant Interfaces: A Combined Vibrational Spectroscopy and Capacitance Study.

Abstract: Surfactants modulate interfacial processes. In electrochemical CO2 reduction, cationic surfactants promote carbon product formation and suppress hydrogen evolution. The interfacial field produced by the surfactants affects the energetics of electrochemical intermediates, mandating their detailed understanding. We have used two complementary tools-vibrational Stark shift spectroscopy which probes interfacial fields at molecular length scales and electrochemical impedance spectroscopy (EIS) which probes the entire double layer-to study the electric fields at metal-surfactant interfaces. Using a nitrile as a probe, we found that at open-circuit potentials, cationic surfactants produce larger effective interfacial fields (∼-1.25 V/nm) when compared to anionic surfactants (∼0.4 V/nm). At a high bulk surfactant concentration, the surface field reaches a terminal value, suggesting the formation of a full layer, which is also supported by EIS. We propose an electrostatic model that explains these observations. Our results help in designing tailored surfactants for influencing electrochemical reactions via the interfacial field effect.

Improvement in Long-Term and High-Temperature Retention Stability of Ferroelectric Field-Effect Memory Transistors With Metal–Ferroelectric–Metal–Insulator–Semiconductor Gate-Stacks Using Al-Doped HfO 2 Thin Films

Abstract: Nonvolatile memory characteristics of the ferroelectric field-effect transistors (FeFETs) were investigated by introducing the metal–ferroelectric–metal–insulator–semiconductor (MFMIS) gate-stacks, employing Al-doped HfO2 (Al:HfO2) ferroelectric thin films. The obtained memory window (MW) of the MFMIS FETs increased from 1.0 to 2.8 V by increasing the areal ratios of the metal–insulator–semiconductor (MIS) to the metal–ferroelectric–metal (MFM) (SI/SF) from 8 to 32. The device with an SI/SF ratio of 16 exhibited a 3-order-of-magnitude on/off memory margin even with a program pulse duration of 500 ns. The long-term data retention was also verified by improving the tolerance against the depolarization field by introducing the MFMIS gate-stacks, which can use fully saturated polarization. The temperature-dependent memory performance and operational reliabilities of the MFMIS-FETs were also investigated at high temperatures to exploit fully the thermal stability of the Al:HfO2. The obtained MWs were not markedly degraded for a retention time of 104 s from room temperature (RT) to 80 °C.

Light and Heat Triggering Modulation of the Electronic Performance of a Graphdiyne-Based Thin Film Transistor.

Abstract: Graphdiyne-based field effect thin film transistors (GTFTs) with a clean, efficient, nondestructive, continuous, and reversible modulation strategy have been developed for the first time. We have determined that efficient electronic modulation utilizing light and heat results in a significant improvement in GTFT performance. Heat can increase the switching ratio of the device to 103, while light regulation can induce a higher switching ratio of >104 by efficient charge injection with an improved conductivity of 1.5 × 104 S/m. Via the adjustment of the visible light wavelength and power density, tunable charge injection has been realized. These results not only highlight the excellent intrinsic properties and modulation method of GTFTs but also promote the application of such films composed of two-dimensional graphdiyne material in integrated devices, such as logic devices and flexible devices.

Effect of large work function modulation of MoS2 by controllable chlorine doping using a remote plasma

Abstract: Adjusting the intrinsic properties of 2-dimensional (2D) transition metal dichalcogenide materials is important for their various applications in electronic devices. Among them, molybdenum disulfide (MoS2) is one of the most attractive layered 2D materials because of its excellent electrical properties as well as good thermal and oxidation stability. Controlling the doping process and analyzing how the dopant atoms affect the device properties are crucial for advanced applications of TMDs. In this study, a simple and controllable chlorine doping method of MoS2 using a remote inductively coupled plasma (ICP) was studied and the effect of doping on the properties of MoS2 was investigated by adjusting the work function of MoS2. Kelvin probe force microscopy (KPFM) shows a gradual decrease of the work function with increasing chlorine radical treatment time. Chlorine doped MoS2 field effect transistors (FETs) exhibited improved electrical characteristics such as the field effect mobility and on current level as demonstrated by the transfer characteristics (Id–Vgs). Especially, the chlorine doped MoS2 FETs showed increased photoresponsivity by 1.94 times (from 424 to 824 A W−1) for green light (λ = 520 nm) and, much more interestingly, 8.59 times (from 37.6 to 323 A W−1) for near-infrared (NIR) light (λ = 785 nm).

Anisotropic thermoelectric effect and field-effect devices in epitaxial bismuthene on Si (111).

Abstract: This experimental study reveals intriguing thermoelectric effects and devices in epitaxial bismuthene, two-dimensional (2D) bismuth with thickness ⩽30 nm, on Si (111). Bismuthene exhibits interesting anisotropic Seebeck coefficients varying 2-5 times along different crystal orientations, implying the existence of a puckered atomic structure like black phosphorus. An absolute value of Seebeck coefficient up to 237 μV K-1 sets a record for elemental Bi ever measured to the best of our knowledge. Electrical conductivity of bismuthene can reach up to 4.6 × 104 S m-1, which is sensitive to thickness and magnetic field. Along with a desired low thermal conductivity ∼1.97 W m-1 K that is 20% of its bulk form, the first experimental zT value at room temperature for bismuthene was measured ∼10-2, which is much higher than many other VA Xenes and comparable to its bulk compounds. Above results suggest a mixed buckled and puckered Bi atomic structure for epitaxial 2D bismuth on Si (111). Our work paves the way to explore potential applications, such as heat flux sensor, energy converting devices and so on for bismuthene.

On ion transport regulation with field-effect nonlinear electroosmosis control in microfluidics embedding an ion-selective medium.

Abstract: We study herein numerically the use of induced-charge electrokinetic phenomena to enable a flexible control of ion transport of dilute electrolyte in a straight ion concentration polarization system. The effect of three convection modes of induced-charge electrokinetic phenomena, including induced-charge electroosmosis, flow-field effect transistor, and alternating-current electroosmosis (ACEO), on convective arrestment of diffusive wave-front propagation is investigated by developing a cross-scale and fully coupled transient numerical simulation model, wherein multiple frequency electrochemical polarization and nonlinear diffuse charge dynamics in spatiotemporally varying solution conductivity are taken into account. We demonstrate by detailed comparative simulation studies that ACEO vortex flow field above a metal strip array arranged along the anodic chamber's bottom surface serves as the most efficient way for adjusting the salt density distribution at micrometer and even millimeter dimension, due to its high flexibility in controlling the stirring flow state with the introduction of two extra electrical parameters. The specific operating status is determined by whether the electrode array is floating in potential (induced-charge electroosmosis) or biased to ground (flow-field effect transistor) or forced to oscillate at another Fourier mode (ACEO). These results prove useful for on-chip electric current control with electroconvective stirring.

High Performance Transparent a-IGZO Thin Film Transistors With ALD-HfO 2 Gate Insulator on Colorless Polyimide Substrate

Abstract: High performance and transparent amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFT) have been successfully fabricated on the colorless polyimide plastic substrate using a high quality HfO2 dielectric film formed by the low temperature atomic layer deposition process as the gate insulator. Besides, the effects of source/drain material, ITO film and Mo metal, are also studied and compared in this work. With the optimized process condition, the devices with ITO source/drain exhibit a high ION/IOFF current ratio of ∼4.25 × 1011, a lower sub-threshold swing value of 0.087 V/decade, a desirable positive threshold voltage value of 0.1379 V and an acceptable field effect mobility of 19.69 cm2/Vs. while it also shows excellent reliability characteristic and low hysteresis. These results may appear highly promising potentials for the next generation fully transparent flexible display application.

Catalytically mediated epitaxy of 3D semiconductors on van der Waals substrates

Abstract: The formation of well-controlled interfaces between materials of different structure and bonding is a key requirement when developing new devices and functionalities. Of particular importance are epitaxial or low defect density interfaces between two-dimensional materials and three-dimensional semiconductors or metals, where an interfacial structure influences electrical conductivity in field effect and optoelectronic devices, charge transfer for spintronics and catalysis, and proximity-induced superconductivity. Epitaxy and hence well-defined interfacial structure has been demonstrated for several metals on van der Waals-bonded substrates. Semiconductor epitaxy on such substrates has been harder to control, for example during chemical vapor deposition of Si and Ge on graphene. Here, we demonstrate a catalytically mediated heteroepitaxy approach to achieve epitaxial growth of three-dimensional semiconductors such as Ge and Si on van der Waals-bonded materials such as graphene and hexagonal boron nitride. Epitaxy is “transferred” from the substrate to semiconductor nanocrystals via solid metal nanocrystals that readily align on the substrate and catalyze the formation of aligned nuclei of the semiconductor. In situ transmission electron microscopy allows us to elucidate the reaction pathway for this process and to show that solid metal nanocrystals can catalyze semiconductor growth at a significantly lower temperature than direct chemical vapor deposition or deposition mediated by liquid catalyst droplets. We discuss Ge and Si growth as a model system to explore the details of such hetero-interfacing and its applicability to a broader range of materials.

Quantum Confinement Effect in Amorphous In-Ga-Zn-O Heterojunction Channels for Thin-Film Transistors

Abstract: Electrical and carrier transport properties in In–Ga–Zn–O thin-film transistors (IGZO TFTs) with a heterojunction channel were investigated. For the heterojunction IGZO channel, a high-In composition IGZO layer (IGZO-high-In) was deposited on a typical compositions IGZO layer (IGZO-111). From the optical properties and photoelectron yield spectroscopy measurements, the heterojunction channel was expected to have the type–II energy band diagram which possesses a conduction band offset (ΔEc) of ~0.4 eV. A depth profile of background charge density indicated that a steep ΔEc is formed even in the amorphous IGZO heterojunction interface deposited by sputtering. A field effect mobility (μFE) of bottom gate structured IGZO TFTs with the heterojunction channel (hetero-IGZO TFTs) improved to ~20 cm2 V−1 s−1, although a channel/gate insulator interface was formed by an IGZO−111 (μFE = ~12 cm2 V−1 s−1). Device simulation analysis revealed that the improvement of μFE in the hetero-IGZO TFTs was originated by a quantum confinement effect for electrons at the heterojunction interface owing to a formation of steep ΔEc. Thus, we believe that heterojunction IGZO channel is an effective method to improve electrical properties of the TFTs.

Correlation between Kink effect and trapping mechanism through H1 hole trap in Al 0.22 Ga 0.78 N/GaN/SiC HEMTs by current DLTS: field effect enhancement

Abstract: A cryogenic investigation of the Kink effect with drain-source bias sweeping process during output characteristics is suggested An exhaustive study of the field effect dependence on the emission rate from hole traps in AlGaN/GaN HEMT transistors has been realized by means of current DLTS spectroscopy (I-DLTS) We have found that the Kink effect was induced by impact ionization of electron trapped in acceptor-like deep levels with activation energies at about 085 eV overhead the valence band of the GaN buffer layer Using I-DLTS method, three holes traps, labeled A, H1, and H5, have been distinguished The H1 deep level might correspond to the carbon substituting the N site (CN) which is supposed to be the main cause of the Kink effect The major H5 trap seems to be gallium vacancy complex (VGa–ON) For the hole trap H1, the phonon-assisted tunneling emission is the dominant mechanism for holes to escape from the trapping centers while for the H5 trap their field dependence shows a classical pure tunneling effect

Electromagnetically induced grating in double quantum dot system

Abstract: Electromagnetically induced grating (EIG) in the ladder-plus-Y double quantum dot system is modeled and the diffraction grating properties are explored in this structure. A high transmission function is obtained under the high pump field. This function is reduced under increasing the probe field due to the Kerr effect. The phase of this function depends on pumping. It is shown that the application of another two fields from the wetting layer (WL)-quantum dot (QD) type is more efficient in obtaining very high diffraction intensity. So, EIG with high diffraction intensity is obtained under a four-field application. Note that, WL-QD field effect is not studied earlier. Neglecting the WL effect reduces the transmission by five times. The diffraction intensity of this system is six times higher than that obtained from a single QD structure.

Field-effect passivation of metal/n-GaAs Schottky junction solar cells using atomic layer deposited Al2O3/ZnO ultrathin films

Abstract: In this paper, a novel field-effect passivation technique is used to improve the photovoltaic properties of metal/n-GaAs Schottky junction solar cells. In this technique, a relatively large density of positive or negative fixed charges existing at the top surface of the dielectric thin films is used to create an electric field gradient to prevent the photogenerated charge carriers from recombining. Atomic layer deposition is used to grow high-quality Al2O3 and ZnO ultrathin films that are used as passivating materials. Electrical measurements demonstrate an improvement in both diodelike and photovoltaic properties of Schottky solar cells in the proposed stacked Al2O3/ZnO passivation structure compared to the single Al2O3 layer. This can be attributed to both higher equivalent capacitance/permittivity of the stacked passivation layer and increased density of negative fixed charges at the interface of the passivation layer and the semiconductor.

Detection of Glycated Albumin Using a Novel Field Effect Aptasensor

Abstract: In this paper, we propose a new field effect (FE) sensor for fast detection of glycated albumin (GA) based on thiol modified aptamer (TMA). A p-type Si/ (100 nm) SiO2 wafer was used, where the SiO2 layer acts as the gate insulator. This gate insulator is then decorated with a layer of randomly oriented ZnO nanorods, coated with 40 nm of Au to act as binding sites for the TMA. We have shown that the addition of GA significantly reduces the conductivity of the p-type Si channel, which can be used to determine the GA concentration in the test solution. The ZnO/Au/TMA/GA layer can induce negative charges in the Si channel underneath the gate insulator, which is followed by the depletion of the positively charged carriers of the Si, decreasing the conductivity. Accordingly, the charge carriers in the Si channel show a steady decline with increasing GA concentration. We have shown that this decrease in conductivity can be further tuned by varying the gate voltage. The sensor presented here can be used as a fast and reliable sensor for determination of GA.

Modeling Field Effect in Black Silicon and Its Impact on Device Performance

Abstract: Black silicon (b-Si) has improved the performance of solar cells and photodetectors due to the excellent optics and surface passivation achieved with atomic layer deposition (ALD) dielectric films. One major reason for the success is the strong field effect caused by the high density of fixed charges present in the dielectric. Depending on the device, the field effect can be utilized also in a more active role than for mere surface passivation, including the formation of floating and/or induced junctions in silicon devices. However, in order to utilize the field effect efficiently, a deeper understanding of the thin-film charge-induced electric field and its effects on charge carriers in b-Si is required. Here, we investigate the field effect in b-Si using the Silvaco Atlas semiconductor device simulator. By studying the electric field and charge-carrier profiles, we develop a model where the electrical properties of b-Si can be approximated with a planar surface, which significantly simplifies the device-level simulations. We validate the model by simulating the spectral response of a b-Si -induced junction photodiode achieving less than 1% difference compared with experimental device performance in a wide range of wavelengths. Finally, we apply the model to study how variation in surface recombination velocity affects the short-wavelength sensitivity and dynamic range in a b-Si photodiode.

Hysteresis in graphene nanoribbon field-effect devices.

Abstract: Hysteresis in the current response to a varying gate voltage is a common spurious effect in carbon-based field effect transistors. Here, we use electric transport measurements to probe the charge transport in networks of armchair graphene nanoribbons with a width of either 5 or 9 carbon atoms, synthesized in a bottom-up approach using chemical vapor deposition. Our systematic study on the hysteresis of such graphene nanoribbon transistors, in conjunction with temperature-dependent transport measurements shows that the hysteresis can be fully accounted for by trapping/detrapping carriers in the SiO2 layer. We extract the trap densities and depth, allowing us to identify shallow traps as the main origin of the hysteresis effect.

Electric field thermopower modulation analyses of the operation mechanism of transparent amorphous SnO$_2$ thin-film transistor

Abstract: Transparent amorphous oxide semiconductors (TAOSs) based transparent thin-film transistors (TTFTs) with high field effect mobility are essential for developing advanced flat panel displays. Among TAOSs, amorphous (a-) SnO$_2$ has several advantages against current a-InGaZnO4 such as higher field effect mobility and being indium free. Although a-SnO$_2$ TTFT has been demonstrated several times, the operation mechanism has not been clarified thus far due to the strong gas sensing characteristics of SnO$_2$. Here we clarify the operation mechanism of a-SnO$_2$ TTFT by electric field thermopower modulation analyses. We prepared a bottom-gate top-contact type TTFT using 4.2-nm-thick a-SnO$_2$ as the channel without any surface passivation. The effective thickness of the conducting channel was ~1.7 + - 0.4 nm in air and in vacuum, but a large threshold gate voltage shift occurred in different atmospheres; this is attributed to carrier depletion near at the top surface (~2.5 nm) of the a-SnO$_2$ due to its interaction with the gas molecules and the resulting shift in the Fermi energy. The present results would provide a fundamental design concept to develop a-SnO$_2$ TTFT.

Metal to semiconductor transition of two-dimensional NbSe2 through hydrogen adsorption: A first-principles study

Abstract: Based on first-principles calculations, we predict that the recently synthesized two-dimensional (2D) NbSe2 can be changed from the metallic to the semiconducting phase upon the adsorption of H with an indirect bandgap of 2.99 eV. The bandgap opening of the 2D NbSe2 only occurs when the hydrogen coverage is high, and it is sensitive to mechanical strain. The hydrogenated 2D NbSe2 is dynamically stable under a tensile strain of up to 9%, whereas a compressive strain leads to instability of the system. The optical spectra obtained from the GW-Bethe–Salpeter equation calculations suggest that 2D NbSe2 is highly isotropic, and it will not affect the polarization of light along the x- or y-direction. The optical bandgap, describing the transition energy of the exciton, is sensitive to the mechanical strain with the calculated exciton binding energy of ∼0.42 eV. These intriguing properties suggest that H functionalized 2D NbSe2, grown on a substrate with a larger lattice parameter, can be used to modulate the bandgap of NbSe2. This is beneficial in developing a nanoscale field effect and optoelectronic devices.

Enhanced Photovoltaic and Photocatalytic Activity of Flower-Like Fe2WO6/WO3Contact Layers

Abstract: Tungsten oxide hydrate (WO3·H2O) nanoparticle and Iron tungstate/tungsten oxide (Fe2WO6/WO3) nanocomposite have been synthesized via a facile hydrothermal route. Structural, optical, morphological and electrical properties of the synthesized samples were characterized by X-ray powder diffraction (XRD), UV-Visible spectroscopy, Field effect scanning electron microscopy (FE-SEM) with Energy-dispersive X-ray spectroscopy (EDX) and DC electrical conductivity measurement respectively. The powder X-ray diffraction (XRD) results confirm the formation of Fe2WO6/WO3 nanocomposite. Variation in the electrical conductivity and activation energy was studied by DC electrical conductivity studies. Fe2WO6/WO3 nanocomposites show a significant enhancement in the degradation of methyl blue than WO3·H2O nanoplates. The significant enhancement was due to flower-like morphology and the narrowing of the optical band gap which reduces the electron-hole pair recombination rate. The dye-sensitized solar cell (DSSC) was fabricated using WO3·H2O and Fe2WO6/WO3 films as photoanodes and it was observed that Fe2WO6/WO3 photoanode shows highest power conversion efficiency (PCE) i.e., 4.69% which can be achieved through high dye absorbing capacity.

Self-Mixing Model of Terahertz Rectification in a Metal Oxide Semiconductor Capacitance

Abstract: Metal oxide semiconductor (MOS) capacitance within field effect transistors are of great interest in terahertz (THz) imaging, as they permit high-sensitivity, high-resolution detection of chemical species and images using integrated circuit technology. High-frequency detection based on MOS technology has long been justified using a mechanism described by the plasma wave detection theory. The present study introduces a new interpretation of this effect based on the self-mixing process that occurs in the field effect depletion region, rather than that within the channel of the transistor. The proposed model formulates the THz modulation mechanisms of the charge in the potential barrier below the oxide based on the hydrodynamic semiconductor equations solved for the small-signal approximation. This approach explains the occurrence of the self-mixing process, the detection capability of the structure and, in particular, its frequency dependence. The dependence of the rectified voltage on the bias gate voltage, substrate doping, and frequency is derived, offering a new explanation for several previous experimental results. Harmonic balance simulations are presented and compared with the model results, fully validating the model’s implementation. Thus, the proposed model substantially improves the current understanding of THz rectification in semiconductors and provides new tools for the design of detectors.

Correlation between corrugation-induced flexoelectric polarization and conductivity of low-dimensional transition metal dichalcogenides

Abstract: Tunability of polar and semiconducting properties of low-dimensional transition metal dichalcogenides (TMDs) have propelled them to the forefront of fundamental and applied physical research. These materials can vary from non-polar to ferroelectric, and from direct-band semiconductor to metallic. However, in addition to classical controls such as composition, doping, and field effect in TMDs the additional degrees of freedom emerge due to the curvature-induced electron redistribution and associated changes in electronic properties. Here we numerically explore the elastic and electric fields, flexoelectric polarization and free charge density for a TMD nanoflake placed on a rough substrate with a sinusoidal profile of the corrugation using finite element modelling. Numerical results for different flake thickness and corrugation depth yield insight into the flexoelectric nature of the out-of-plane electric polarization and establish the unambiguous correlation between the polarization and static conductivity modulation caused by inhomogeneous elastic strains coupled with deformation potential and strain gradients, which evolve in TMD nanoflake due to the adhesion between the flake surface and corrugated substrate. We revealed a pronounced maximum at the thickness dependences of the electron and hole conductivity of MoS2 and MoTe2 nanoflakes placed on a metallic substrate, which opens the way for their geometry optimization towards significant improvement their polar and electronic properties, necessary for their advanced applications in nanoelectronics and memory devices.Specifically, obtained results can be useful for elaboration of nanoscale straintronic devices based on the bended MoS2, MoTe2 and MoSTe nanoflakes, such as diodes and bipolar transistors with a bending-controllable sharpness of p-n junctions.

Influence of Non-Uniform Interface Defect Clustering on Field-Effect Mobility in SiC MOSFETs Investigated by Local Deep Level Transient Spectroscopy and Device Simulation

Abstract: It has recently been shown that interface defect density (Dit) at SiO2/SiC interfaces can have non-uniform clustered distribution through the measurement by local deep level transient spectroscopy (local DLTS). Here we investigate the influence of the non-uniform Dit clustering on the field-effect mobility in SiC metal-oxide-semiconductor field effect transistors (MOSFETs) by device simulation. We develop a three dimensional numerical model of a SiC MOSFET, which can incorporate actual Dit distributions measured by local DLTS. Our main result is that the impact of the non-uniform Dit clustering on field-effect mobility is negligible for a SiC MOSFET with high Dit formed by dry thermal oxidation but it becomes significant for that with lower Dit by post-oxidation annealing. The result indicates that channel mobility can be further improved by making Dit distribution uniform as well as reducing Dit.

Temperature Dependence of Field-Effect Thermoelectric Power in Rubrene Crystals

Abstract: Gate-induced carrier concentration dependence of electrical conductivity σ and thermoelectric power S of rubrene crystals is investigated down to low temperatures (T) using laser heating, and the r...

Recent progress in silicon carbide field effect gas sensors

Abstract: The introduction of silicon carbide as the semiconductor in gas-sensitive field effect devices has disruptively improved this sensor platform extending the operation temperature to more than 600 °C ...

Demonstration of electric double layer gating under high pressure by the development of field-effect diamond anvil cell

Abstract: 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.