Dielectric Engineering Research Articles

Design and analysis of Z shaped InGa0.5As0.5/Si tunnel FET using non-equilibrium Green’s function model for hydrogen gas sensing application

—In this paper, a high-k stacked gate Z shaped hetero-juncture TFET (Z-HTFET) is introduced as transducer sensor for the application of hydrogen gas detection. The positioning of stacked gate over the entire source region resulting Z shaped TFET exhibits vertical line tunneling mechanism between the source and the channel yielding higher ON state current (Id) as compared to conventional double gate (DG) TFET. Further, the combination of low band gap source of In0.5Ga0.5As and hetero-gate dielectric engineering helps to facilitate improved device current, steeper subthreshold slope and lower leakage current (Ileak) conduction. Here, palladium (Pd) and the high-k gate stack (HfO2/SiO2) is used as the sensing platform. The induced shift in work function of Pd gate electrode due to the dissociation and diffusion of hydrogen gas molecules into the catalytic gate metal is considered as the detection metric for calculating the sensitivity of the proposed TFET based gas sensor. The behavior of the hydrogen gas sensor is studied using numerical device simulator in terms of surface potential, electric field, transfer characteristics, transconductance, Id/Ileak ratio with variation in work-function and finally Id/Ileak sensitivity is measured. The sensor behavior for a wide range of temperature is also examined to explore the temperature stability of the device. The comparative performance analysis of Z-HTFET with sensitivity of 95.26% establishes the superiority of the device for hydrogen gas sensing as compared to some of the recently reported FET based sensors.

Pushing the Limits of Biosensing: Selective Calcium Ion Detection with High Sensitivity via High-k Gate Dielectric Engineered Si Nanowire Random Network Channel Dual-Gate Field-Effect Transistors.

Calcium ions (Ca2+) are abundantly present in the human body; they perform essential roles in various biological functions. In this study, we propose a highly sensitive and selective biosensor platform for Ca2+ detection, which comprises a dual-gate (DG) field-effect transistor (FET) with a high-k engineered gate dielectric, silicon nanowire (SiNW) random network channel, and Ca2+-selective extended gate. The SiNW channel device, which was fabricated via the template transfer method, exhibits superior Ca2+ sensing characteristics compared to conventional film channel devices. An exceptionally high Ca2+ sensitivity of 208.25 mV/dec was achieved through the self-amplification of capacitively coupled DG operation and an enhanced amplification ratio resulting from the high surface-to-volume ratio of the SiNW channel. The SiNW channel device demonstrated stable and reliable sensing characteristics, as evidenced by minimal hysteresis and drift effects, with the hysteresis voltage and drift rate measuring less than 6.53% of the Ca2+ sensitivity. Furthermore, the Ca2+-selective characteristics of the biosensor platform were elucidated through experiments with pH buffer, NaCl, and KCl solutions, wherein the sensitivities of the interfering ions were below 7.82% compared to the Ca2+ sensitivity. The proposed Ca2+-selective biosensor platform exhibits exceptional performance and holds great potential in various biosensing fields.

Interface engineering of charge-transfer excitons in 2D lateral heterostructures

The existence of bound charge transfer (CT) excitons at the interface of monolayer lateral heterojunctions has been debated in literature, but contrary to the case of interlayer excitons in vertical heterostructure their observation still has to be confirmed. Here, we present a microscopic study investigating signatures of bound CT excitons in photoluminescence spectra at the interface of hBN-encapsulated lateral MoSe2-WSe2 heterostructures. Based on a fully microscopic and material-specific theory, we reveal the many-particle processes behind the formation of CT excitons and how they can be tuned via interface- and dielectric engineering. For junction widths smaller than the Coulomb-induced Bohr radius we predict the appearance of a low-energy CT exciton. The theoretical prediction is compared with experimental low-temperature photoluminescence measurements showing emission in the bound CT excitons energy range. We show that for hBN-encapsulated heterostructures, CT excitons exhibit small binding energies of just a few tens meV and at the same time large dipole moments, making them promising materials for optoelectronic applications (benefiting from an efficient exciton dissociation and fast dipole-driven exciton propagation). Our joint theory-experiment study presents a significant step towards a microscopic understanding of optical properties of technologically promising 2D lateral heterostructures.

Band gap and gate underlap engineered novel Si0.2Ge0.8/GaAs JLTFET with dual dielectric gate for improved wireless applications

This research article introduces a dual dielectric gate, gate-drain underlaps hetero-structure Si0.2Ge0.8/GaAs charge plasma-based junctionless TFET (DDG-GUHJLTFET). In which a first-time combined approach of the band gap, gate underlap, and gate dielectric engineering is applied on a novel Si0.2Ge0.8/GaAs compound to improve the analog/RF attributes of the reported device. The use of Si0.2Ge0.8/GaAs along with dual dielectric material (HfO2 and SiO2) improves the ON-state current (ION), whereas the implementation of the gate-underlap technique suppresses the ambipolar current (IAmb). In terms of DC characteristics, the reported device provides 1370 and 1.8 × 108 times greater ION, ION/IAmb, and 10−5 times and 80.2 % lower IAmb, SS, compared to traditional Si-JLTFET, respectively. In addition, DDG-GUHJLTFET provides 809.7 times larger transconductance (gm) in comparison to the Si-JLTFET, which led to 1.5 × 103 and 6.3 × 102 times higher cut-off frequency (fT) and maximum oscillation frequency (fmax) respectively, demonstrating its suitability for use in wireless applications.

Sub-Nanosecond 2D Perovskite Scintillators by Dielectric Engineering.

Perovskite materials have demonstrated great potential for ultrafast scintillators with high light yield. However, the decay time of perovskite still cannot be further minimized into sub-nanosecond region, while sub-nanosecond scintillators are highly demanded in various radiation detection, including high speed X-ray imaging, time-of-flight based tomography or particle discrimination, and timing resolution measurement in synchrotron radiation facilities, etc. Here, a rational design strategy is showed to shorten the scintillation decay time, by maximizing the dielectric difference between organic amines and Pb-Br octahedral emitters in 2D organic-inorganic hybrid perovskites (OIHP). Benzimidazole (BM) with low dielectric constant inserted between [PbBr6 ]2- layers, resulting in a surprisingly large exciton binding energy (360.3 ± 4.8 meV) of 2D OIHP BM2 PbBr4 . The emitting decay time is shortened as 0.97ns, which is smallest among all the perovskite materials. Moreover, the light yield is 3190photonsMeV-1 , which is greatly higher than conventional ultrafast scintillator BaF2 (1500photonsMeV-1 ). The rare combination of ultrafast decay time and considerable light yield renders BM2 PbBr4 excellent performance in γ-ray, neutron, α-particle detection, and the best theoretical coincidence time resolution of 65.1ps, which is only half of the reference sample LYSO (141.3ps).

Enhancement of device characteristics of CNT-TFET: Role of electrostatic doping and work function engineering

In this work, an Electrostatic Doped Carbon Nanotube Tunneling FET (ED CNT-TFET) has been designed and simulated using a work function engineering technique. An intrinsic CNT is introduced as a channel material and a doped pocket is created between the source and the channel by utilizing an appropriate work function to boost the ON-state current of the device. Moreover, dielectric pocket engineering is applied to boost the high-frequency performance. The simulations, performed in this work, are conducted through a 2D solution of Poisson and Schrodinger equations which are done by utilizing the unbalanced Green function formalism. Simulation results demonstrate that the proposed device structure could improve the ON-current, cut-off frequency, and achieve a low subthreshold swing (SS) value which makes it suitable for low power applications. Additionally, the presented structure could also eliminate ambipolar conduction.

Transverse dielectric and lateral channel band engineering of drain-side and source-side injection in Ge-based charge-trapping memory cells for energy-efficient applications

Transverse dielectric and lateral channel band engineering of drain-side and source-side injection in Ge-based charge-trapping memory cells for energy-efficient applications

Modulating Charge Transport from Thermally Activated to “Band‐Like” Through Interfacial Bottom‐Up Binding Capability of Bilayer Polymer Dielectrics

AbstractThe disordered chain arrangement of polymer dielectrics has complex both internal and external effects on system performance, which generally stimulates the weak acquisition and grain boundaries of vapor‐deposited organic small molecule films (VDOSMFs) with thermally activated charge transport. As a result, achieving “band‐like” transmission of VDOSMs on polymer dielectrics is attempting to prove to be a major challenge. Three types of bi‐polymer dielectrics are developed to modulate charge transport from thermally activated mode to “band‐like” transport at the interfacial level. The bottom consisting of a polyimide layer is critical to interfacial modulation, which shows the selectively binding capability with up‐dielectric layers to realize the modulation of charge transport, as corroborated by interface characterization and density functional‐based tight‐binding calculation. The findings provide an effective strategy for modulating the charge transport through polymer dielectric engineering and also recommend a podium to further comprehend the electrical characteristics of small molecules in organic thin‐film transistors.

Exploring the effect of dielectric screening on neutral and charged-exciton properties in monolayer and bilayer MoTe2

Dielectric engineering of heterostructures made from two-dimensional van der Waals semiconductors is a unique and powerful tool to tailor the electric and optical band gaps solely via the dielectric environment and the crystal thickness modulation. Here, we utilize high quality MoTe2 monolayer and bilayer crystals as a candidate for near-infrared photonic applications. The crystals are exfoliated on various technologically relevant carrier substrates: silicon/silicon dioxide, poly(methyl methacrylate), hexagonal boron nitride, silicon carbide, and silicon nitride. These substrates provide a large range of high frequency dielectric constants from 2.1 to 7.0 for MoTe2-containing heterostructures. We assess the relationship between the environmental dielectric function and Coulomb screening by combining detailed spectroscopic measurements, utilizing low-temperature and high-spatially resolved photoluminescence and contrast reflectivity, with microscopic many-body modeling, to explore the potential of this less-recognized material platform for applications in optoelectronics at photon wavelengths above 1 μm. We observe a redshift of the optical gap emission energy from the monolayer to bilayer regime on the order of 30 meV. Furthermore, the thickness controlled shift is slightly larger than the one induced by the local dielectric environment, which ranges on the order of 20 meV for the MoTe2 monolayers and on the order of 8 meV for the MoTe2 bilayers. We also show that the local dielectric screening barely affects the trion binding energy, which is captured by our microscopic model, accounting for the screened Coulomb potential for the heterostructures.

Ambipolar‐To‐Unipolar Conversion in Ultrathin 2D Semiconductors

Achieving the full potential of any semiconductor device needs an understanding and precise control of carrier transport behavior, which significantly affects the stability and power consumption in future large‐scale integrated circuits. Compared to other semiconductor materials, bipolar 2D semiconductor materials often face difficulty in turning off channel currents, which seriously challenges the development of low‐power semiconductor devices. Here, a review of the studies on transforming ambipolar conduction in 2D materials to get unipolar p‐type/n‐type semiconductors is presented. In particular, 2D semiconductors of black phosphorus and transition metal dichalcogenides such as WSe2 and MoTe2 are investigated. The intrinsic and extrinsic factors that can directly affect the behavior of carriers, such as contact engineering, chemical doping, surface charge transfer doping, electrostatic gating, and dielectric engineering, are focused. Furthermore, how these ambipolar‐to‐unipolar conversion strategies can be applied to tune device performance and construct new‐structure electronic and optoelectronic devices are showcased. Finally, the most critical challenges and future developments in ambipolar‐to‐unipolar conversion engineering in 2D materials are summarized.

Impact of band gap and gate dielectric engineering on novel Si0.1Ge0.9-GaAs lateral N-type charge plasma based JLTFET

In this research article, a device called dual dielectric gate hetero-material junctionless TFET (DD-HJLTFET) is proposed using a novel amalgamation of Si0.1Ge0.9/GaAs for the first time and investigated by a Silvaco -ATLAS simulator 5.26.1.R version. This device utilizes a Si1-xGex (x = 0.9) at the source and GaAs at the drain and channel, along with dual dielectric materials (HfO2, SiO2) at the gates. Its electrical performance has improved significantly compared to the latest published literature results on TFET and traditional Si-JLTFET. Simulation results show that DD-HJLTFET provides superior performance in terms of analog/RF, linearity, and intermodulation distortion FOMs as ION (32100%↑), SS (66%↓), gm (20233%↑), TGF (324.7 times↑), Av (199.3%↑), Cgg (171%↓), fT (557.41 times↑), GBP (560.6 times↑), and various signal performance parameters such as VIP2 (116.3%↑), IIP3 (40.5%↑), 1-dB compression point (9.6%↑) compared to Si-JLTFET. Therefore, the DD-HJLTFET device proposed in this article can be suitable for high-frequency and low-power applications.

Continuous Color-Tunable Light-Emitting Devices Based on Compositionally Graded Monolayer Transition Metal Dichalcogenide Alloys.

The diverse series of transition metal dichalcogenide (TMDC) materials has been employed in various optoelectronic applications, such as photodetectors, light-emitting diodes, and lasers. Typically, the detection or emission range of optoelectronic devices is unique to the bandgap of the active material. Therefore, to improve the capability of these devices, extensive efforts have been devoted to tune the bandgap, such as gating, strain, and dielectric engineering. However, the controllability of these methods is severely limited (typically ≈0.1eV). In contrast, alloying TMDCs is an effective approach that yields a composition-dependent bandgap and enables light emissions over a wide range. In this study, a color-tunable light-emitting device using compositionally graded TMDC alloys is fabricated. The monolayer WS2 /WSe2 alloy grown by chemical vapor deposition shows a spatial gradient in the light-emission energy, which varies from 2.1 to 1.7eV. This alloy is incorporated in an electrolyte-based light-emitting device structure that can tune the recombination zone laterally. Thus, a continuous and reversible color-tunable light-emitting device is successfully fabricated by controlling the light-emitting positions. The results provide a new approach for exploring monolayer semiconductor-based broadband optical applications.

Analytical modelling and sensitivity analysis of Gallium Nitride-Gate Material and, dielectric engineered- Schottky nano-wire fet(GaN-GME-DE-SNW-fet) based label-free biosensor

An analytical model of nanogap embedded Gallium Nitride Gate- Material and Dielectric Engineered- Schottky Nano-Wire Field Effect Transistor (GaN-GME-DE-SNW-FET) for implementation as a label-free biosensor is introduced. An expression for the surface potential is attained by resolving the 1-D Poisson equation and 2-D Laplace equation utilizing a superposition method. A Model for the threshold voltage is also developed to analyze the sensitivity of the biosensor. The projected model also contains the repercussion of barrier height dropping at the metal-semiconductor intersection along with Dielectric Engineering (DE) using high-k (HfO2) material and Gate Material Engineering (GME) using metal m1with workfunctionφm1and m2with workfunctionφm2. The sensitivity of biosensor's has been studied for diverse dielectric constant and charge densities immobilized within the nanogap cavity. A comparative study has also been done between Gallium nitride-based (GaN- GME-DE-SNW-FET) and Silicon-based (Si-GME-DE-SNW-FET) Label-free biosensors. The developed analytical model is verified and validated using ATLAS- TCAD device simulations.

Comparative Analysis of Dielectric Engineered Tunnel FET for Biosensing Applications

Comparative Analysis of Dielectric Engineered Tunnel FET for Biosensing Applications

Halogen tuning toward dielectric switch and band gap engineering in one-dimensional hybrid materials

Organic-inorganic hybrids with multiple tunable functions are very attractive for potential applications in sensors, smart switches, etc. To investigate the effect of halogen tuning on the properties of hybrid materials, two new multifunctional organic-inorganic hybrid compounds [3-hydroxy-azetidinecation]2SbX5 (1: X = Cl; 2: X = Br) are successfully synthesized here by replacing halogen anions. Reversible structural phase transitions accompanied by anomalous changes in dielectric constants are found when heating (T1 = 362 K; T2 = 373 K). Both two compounds have the same space group change from P212121 (Low Temperature Phase) to Pnma (High Temperature Phase). When replacing Cl with Br, the phase transition temperature increases by ca. 10 K and the band gap changes from 3.21 eV to 2.75 eV. Based on the above properties, this work could provide an effective molecular design strategy for the exploration and construction of temperature-tunable, lower bandgap semiconductor hybrid materials.

A high-k Cu-doped ZnO film formed via Ga-ion implantation: The acceptor-donor co-doping approach

Dielectric thin films having high permittivity (high-k) and low dielectric loss is essential for developing high performance capacitive devices like metal oxide field effect transistor or thin film transistor. Ga ion implantation performed on Cu-doped ZnO film fabricated by pulsed laser deposition with optimized doping concentrations and post-implantation annealing yielded film having high permittivity and low dielectric loss (ε = 87 and tan δ = 0.17 at the frequency of 1 kHz). Moreover, the permittivity exhibits good stability over a wide range of frequency from 20 Hz to 10 MHz. The high-k film was characterized by detailed dielectric studies, including frequency dependence of permittivity and dielectric loss, complex electrical modulus analysis, impedance spectroscopy and ac conductivity. The enhancement of the permittivity was attributed to the correlated potential barrier hopping of electrons between the neighboring acceptor-donor defect complex states in the band gap created by the co-doping, thus acting as electric dipoles polarizing the film. This work opens up future possibility for ‘dielectric engineering’. The three-dimensional dielectric spatial profile can be controlled via the selective area ion implantation with the depth controlled by the ion implantation energy. • A high-k Ga-Cu co-doped ZnO film formed via pulsed laser deposition and ion implantation method. • Optimized doping concentrations yielded high permittivity and low dielectric loss (ε=87 and tan δ=0.17 at 1 kHz). • Enhancement of permittivity was attributed to the correlated barrier hopping of electrons between neighboring defect complex.

Dielectric engineering for improvement of mobility and photoelectric performance in 2D BiI3

Two-dimensional (2D) bismuth triiodide (BiI3) has been emerging as a potential layered material for optoelectronic applications due to its air stability and high atomic density. Although much effort has been devoted to improvements of carrier mobility, conductivity and photoelectric response, performance is still very limited. Here, we report a simple and scalable strategy for greatly improving the electrical and optical properties of 2D BiI3 through high-κ dielectric engineering. Upon covering with a high-κ dielectric oxide (Al2O3), air isolation and dielectric screening effects can lead to the reduction of the contact barrier, passivation of trap states, and suppression of Coulomb scattering. As a result, BiI3-based phototransistors can increase carrier mobility by three orders of magnitude and improve photoresponsivity by three orders of magnitude up to 8.05 × 103 A W−1. This work develops a new 2D BiI3 material and efficient dielectric engineering for improving mobility and photoelectrical performance, expanding the family of 2D materials and offering a promising strategy for potential nano-device applications.

Dark-Exciton Driven Energy Funneling into Dielectric Inhomogeneities in Two-Dimensional Semiconductors.

The optoelectronic and transport properties of two-dimensional transition metal dichalcogenide semiconductors (2D TMDs) are highly susceptible to external perturbation, enabling precise tailoring of material function through postsynthetic modifications. Here, we show that nanoscale inhomogeneities known as nanobubbles can be used for both strain and, less invasively, dielectric tuning of exciton transport in bilayer tungsten diselenide (WSe2). We use ultrasensitive spatiotemporally resolved optical scattering microscopy to directly image exciton transport, revealing that dielectric nanobubbles are surprisingly efficient at funneling and trapping excitons at room temperature, even though the energies of the bright excitons are negligibly affected. Our observations suggest that exciton funneling in dielectric inhomogeneities is driven by momentum-indirect (dark) excitons whose energies are more sensitive to dielectric perturbations than bright excitons. These results reveal a new pathway to control exciton transport in 2D semiconductors with exceptional spatial and energetic precision using dielectric engineering of dark state energetic landscapes.

Giant Modulation of the Electron Mobility in Semiconductor Bi2O2Se via Incipient Ferroelectric Phase Transition.

High-mobility layered semiconductors have the potential to enable the next-generation electronics and computing. This paper demonstrates that the ultrahigh electron mobility observed in the layered semiconductor Bi2O2Se originates from an incipient ferroelectric transition that endows the material with a robust protection against mobility degradation by Coulomb scattering. Based on first-principles calculations of electron-phonon interaction and ionized impurity scattering, it is shown that the electron mobility of Bi2O2Se can reach 104 to 106 cm2 V-1 s-1 over a wide range of realistic doping concentrations. Furthermore, a small elastic strain of 1.7% can drive the material toward a unique interlayer ferroelectric transition, resulting in a large increase in the dielectric permittivity and a giant enhancement of the low-temperature electron mobility by more than an order of magnitude. These results establish a new route to realize high-mobility layered semiconductors via phase and dielectric engineering.

Enhanced Analog Performance and High-Frequency Applications of Dielectric Engineered High-K Schottky Nanowire FET

Enhanced Analog Performance and High-Frequency Applications of Dielectric Engineered High-K Schottky Nanowire FET