Frequency Dependence Of Capacitance Research Articles

The dielectric characteristics of spray deposited α-Si3N4:ZnO thin films: The nitride effect on frequency-dependent capacitance and conductance profiles

The study focused on the effect of α-Si3N4 doping on the electrical/dielectric properties of ZnO thin films. Both α-Si3N4 doped and additive-free ZnO thin films were coated on p-Si substrates via a spray deposition method to achieve this. The electrical (current density (J)-voltage (V)) and dielectric properties (capacitance (C), conductance (G), dielectric loss (tanδ), reel/imaginary part of dielectric permittivity (ε′ and ε″) and electric modulus (M′ and M″)) were determined for all samples by using dielectric spectroscopy (DS) method. On the other hand, scanning electron microscopy (FESEM) and energy-dispersive spectroscopy (EDS) analysis were performed to evaluate microstructure, X-ray diffraction (XRD) was used to define chemical composition and atomic-force microscopy (AFM) analysis was carried out to characterise the topology of the coating layers. The thickness/surface roughness was obtained as ∼82.5 nm/10.6 nm for undoped and ̴ 99.5 nm/10.4 nm for nitride-doped samples, respectively. The maximum capacitance value (C) was obtained as 275 pF at −3.0V and 200 Hz, and the optimal conductance (G) value was also found as 45 μS around 4.0V and 1 MHz in the nitride-doped sample. The average of α and τ values was calculated as 5.67 × 10−5 s, 0.146 and 4.49 × 10−5 s, 0.081 for nitride-doped and undoped ZnO, respectively. The increase in performance can be attributed to the homogeneous and almost equally-size distribution of the ZnO grain growth which is strongly controlled by α-Si3N4.

Frequency-dependent capacitance and conductance characteristics and current transport mechanisms of Schottky diodes with TPA-IFA organic interfacial layer

In this study, a Schottky barrier diode with an Al/TPA-IFA/p-Si structure was fabricated using spin coating and thermal evaporation methods. Using forward and reverse bias I–V measurement, we examined the key electrical characteristics of the Al/TPA-IFA/p-Si diode, including Φb, n, Rs, and Nss; we also estimated VD, NA, EF, ∆Φb, WD, Φb and Nss using C–V measurements under the different frequencies (10, 50, 100, 500 kHz, and 1 MHz) at room temperature. Using I–V data and the Thermionic Emission (TE) theory, basic electrical parameters such as ideality factor ( n ), and barrier height ( Φb ) values were computed as 3.01 and 0.716 eV. The fundamental diode parameters are highly frequency-dependent. It was also found that the series Resistance ( Rs ) values reduced with increasing frequency, but the barrier height ( Φb ) and the width of the depletion layer ( WD ) increased. It was found that when frequency increased, the diode capacitance reduced for our new Schottky-type diode. The diode’s potential conduction mechanisms were examined through the utilization of reverse lnI−V0.5 and forward lnI−V graphs. The transport properties of Al/TPA-IFA/p-Si diode are primarily governed by ohmic conduction, Space Charge Limited Current (SCLC), and Trap Charge Limited Current (TCLC) mechanisms at low, moderate, and high voltages, respectively. It was concluded that the Poole–Frenkel Emission (PFE) mechanism was dominant for the Al/TPA-IFA/p-Si diode. Ultimately, the findings confirmed that the TPA-IFA-based diode could be obtained for the electronic application.

Evaluation of Industrial Poly(tert-butyl acrylate) insulated A p-channel Organic Field-Effect Transistor (PtBA-p-OFET)

Poly(tert-butyl acrylate) (PTB-p-A) has been investigated as a promising insulator layer for p-channel organic field effect transistors (p-OFETs) using the p-type semiconductor Poly(3-hexylthiophene-2,5-diyl (P3HT) due to its favorable insulating properties, good film-forming ability and electrical charge separation properties. Top-gate, bottom-contact PTBA-p-OFET devices are fabricated with Indium Thin Oxide (ITO) source/drain electrodes and a P3HT organic semiconductor layer. The frequency-dependent capacitance of the PTBA-p-OFETs was studied through a plot to determine the key parameters, including the threshold voltage (VTh), field-effect mobility (μFET), and the current on/off ratio (Ion/off) of the device. The PTB-p- OFETs exhibit field-effect mobility value of 6.13x10-4 (cm2/V.s), an on/off current ratio of 1.11x102, and a threshold voltage of -15.8 V. The capacitance-frequency characteristics of the capacitor structure were analyzed and found to have as 7.6 nF/cm2 per unit area. This work presents PTBA as a promising for high-performance p-OFET applications.

Detailed analysis of the capacitance characteristic measured using the pseudo-metal–oxide–semiconductor method

This paper discusses the capacitance–voltage (C–V) characteristics of a silicon-on-insulator (SOI) wafer obtained using the alternating current (AC) pseudo-metal–oxide–semiconductor (MOS) method. This study clarified that the C–V characteristics measured using the standard configuration of the AC pseudo-MOS method were strongly ruled by the condition of both the top and back contacts. Using a distinctive setup referred to as the Kelvin AC pseudo-MOS method, coupled with specific treatments applied to the wafer, we acquired C–V and impedance-related characteristics that differed from the standard configuration and aligned with the theoretical expectation for the entire range of measurement frequencies below a few megahertz. In addition, this study demonstrated the qualitative behavior of the frequency-dependent capacitance with the channel conduction of carriers using an analytical model.

Enhancement of the Synaptic Performance of Phosphorus-Enriched, Electric Double-Layer, Thin-Film Transistors

The primary objective of neuromorphic electronic devices is the implementation of neural networks that replicate the memory and learning functions of biological synapses. To exploit the advantages of electrolyte gate synaptic transistors operating like biological synapses, we engineered electric double-layer transistors (EDLTs) using phosphorus-doped silicate glass (PSG). To investigate the effects of phosphorus on the EDL and synaptic behavior, undoped silicate spin-on-glass-based transistors were fabricated as a control group. Initially, we measured the frequency-dependent capacitance and double-sweep transfer curves for the metal-oxide-semiconductor (MOS) capacitors and MOS field-effect transistors. Subsequently, we analyzed the excitatory post-synaptic currents (EPSCs), including pre-synaptic single spikes, double spikes, and frequency variations. The capacitance and hysteresis window characteristics of the PSG for synaptic operations were verified. To assess the specific synaptic operational characteristics of PSG-EDLTs, we examined EPSCs based on the spike number and established synaptic weights in potentiation and depression (P/D) in relation to pre-synaptic variables. Normalizing the P/D results, we extracted the parameter values for the nonlinearity factor, asymmetric ratio, and dynamic range based on the pre-synaptic variables, revealing the trade-off relationships among them. Finally, based on artificial neural network simulations, we verified the high-recognition rate of PSG-EDLTs for handwritten digits. These results suggest that phosphorus-based EDLTs are beneficial for implementing high-performance artificial synaptic hardware.

On the Capacitive-to-Resistive Humidity Response of Polyelectrolyte-Gated Metal Oxide Transistors

The electrolyte gating of transistors, which directly couples ion transport with electron conduction, is particularly interesting in the field of bio and chemical sensing. When a humidity-sensitive polyelectrolyte is used as the gate dielectric, the resulting ionotronic device becomes a humidity-sensitive transistor providing potential advantages in signal amplification and circuit integration. In this work, a humidity-sensitive polyelectrolyte-gated metal oxide transistor is reported by implementing the capacitive-to-resistive-based sensing mechanism. Due to the correlation between drain current and gate capacitance, the measurement of capacitance or impedance for humidity sensors is converted into the measurement of resistance. Initial sensing studies in the quasi-static DC sensing mode resulted in a limited sensing response. A pulsed sensing mode was proposed to considerably enhance the sensing response I D,80%RH /I D,20%RH to 861. The response in the specific RH range was also found to be tunable with the applied sensing signal. The underlying mechanism is elucidated with frequency-dependent capacitance and impedance analysis of the gate electrolyte using corresponding equivalent circuit model.

Synaptic Plasticity Modulation of Neuromorphic Transistors through Phosphorus Concentration in Phosphosilicate Glass Electrolyte Gate.

This study proposes a phosphosilicate glass (PSG)-based electrolyte gate synaptic transistor with varying phosphorus (P) concentrations. A metal oxide semiconductor capacitor structure device was employed to measure the frequency-dependent (C-f) capacitance curve, demonstrating that the PSG electric double-layer capacitance increased at 103 Hz with rising P concentration. Fourier transform infrared spectroscopy spectra analysis facilitated a theoretical understanding of the C-f curve results, examining peak differences in the P-OH structure based on P concentration. Using the proposed synaptic transistors with different P concentrations, changes in the hysteresis window were investigated by measuring the double-sweep transfer curves. Subsequently, alterations in proton movement within the PSG and charge characteristics at the channel/PSG electrolyte interface were observed through excitatory post-synaptic currents, paired-pulse facilitation, signal-filtering functions, resting current levels, and potentiation and depression characteristics. Finally, we demonstrated the proposed neuromorphic system's feasibility based on P concentration using the Modified National Institute of Standards and Technology learning simulations. The study findings suggest that, by adjusting the PSG film's P concentration for the same electrical stimulus, it is possible to selectively mimic the synaptic signal strength of human synapses. Therefore, this approach can positively contribute to the implementation of various neuromorphic systems.

Probing the Recombination Process at the Intermixed Interface of a Solution-Processed Organic Light Emitting Diode By Impedance Spectroscopy

Solution-processed organic light emitting diode (s-OLED) has garnered considerable research interest due to its cost-effectiveness, improved energy efficiency, and material-saving advantages over conventional vacuum deposition methods in OLED production. Recent studies have shown that the thermal annealing process of multilayered s-OLEDs induces intermixing at the interfaces of the layers and enhances the device performance [1,2]. However, the physical origin of the enhanced s-OLED performance by intermixing at the interfaces is poorly understood. To address this issue, we utilized electrical impedance spectroscopy (IS) to investigate the thermal-induced modifications of charge carrier dynamics in a bilayer s-OLED comprising an electron transporting layer (ETL) and an emission layer (EML). We separately assessed the conductance of the ETL and the charge carrier accumulation at the EML/ETL interface by the characteristic relaxation frequency and the plateau at a low frequency regime (20~100 Hz) extracted from the frequency-dependent capacitance spectra, respectively. The IS analysis revealed that improved charge transport in the ETL by thermal annealing process was mainly responsible for the performance enhancement, rather than intermixing at the EML/ETL interface. Notably, we found that annealing the s-OLEDs above the glass transition temperature (Tg) of the ETL, at which significant intermixing occurs, increased the magnitude of negative capacitance, indicating the increased rate of nonradiative trap-assisted recombination [3]. Accordingly, our IS analysis clarified that extended intermixing at the EML/ETL interface is rather detrimental to the performance of s-OLEDs. This study demonstrates that IS can serve as a powerful tool for accurately analyzing charge carrier dynamics in s-OLEDs by simultaneously probing charge transport, interfacial charge accumulation, and recombination processes, thereby providing valuable insights for optimizing s-OLED performance.[1] ACS Appl. Mater. Interfaces 2015, 7 (37), 20779–20785. https://doi.org/10.1021/acsami.5b05818.[2] Advanced Materials Interfaces 2019, 6 (4), 1801627. https://doi.org/10.1002/admi.201801627.[3] Phys. Rev. Lett. 2018, 120 (11), 116602. https://doi.org/10.1103/PhysRevLett.120.116602. Figure caption. The capacitance at 20 Hz and current efficiency at 100 nit are plotted against the ratio of annealing temperature (T) to glass transition temperature (Tg) of ETL. Figure 1

ZnSnN2 Schottky barrier solar cells

The electron density of ZnSnN2 fabricated by different deposition methods is usually much higher than its conduction band density of states and this hinders its device application. By increasing the Zn/Sn atomic ratio of the alloy target, ZnSnN2 with electron density of 1016 cm−3 is fabricated. The obtained ZnSnN2 and silver deposited with radio-frequency sputtering can form Schottky contact which shows photovoltaic effects. The voltage- and frequency-dependent capacitance of the Schottky diodes is further studied. The interface between the Ag-ZnSnN2 is abrupt with interface states of about 1013 eV−1·cm−2 as revealed by the capacitance–voltage curves. The midgap density of states of ZnSnN2 is found to be constant.

Effects of ammonia and oxygen plasma treatment on interface traps in AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors

A HfO2/Al2O3/AlN stack deposited in a plasma-enhanced atomic layer deposition system is used as the gate dielectric for GaN metal–insulator–semiconductor structures. Prior to the deposition, in situ remote plasma pretreatments (RPPs) with O2, NH3, and NH3–O2 (in sequence) were carried out. Frequency-dependent capacitance–voltage (C–V) measurements reveal that for all the RPP-treated samples, the interface trap density Dit was significantly reduced compared to the sample without RPP. In particular, the NH3-treated sample exhibits an extremely low Dit of ∼1011 cm−2·eV−1 from EC − 0.31 eV to EC − 0.46 eV. To characterize the interface traps at deeper levels, the transfer pulsed I–V measurement was employed further. In the energy range of EC − ET > 0.54 eV, the interface trap charge density Qit of various samples demonstrates the following order: NH3 RPP < NH3–O2 RPP < O2 RPP < without RPP. By adjusting multiple pulse widths, the Dit derived from the Qit result matches the C–V measurement precisely. Moreover, X-ray photoelectron spectroscopy analysis of the Ga 3d core-level indicates that NH3 RPP facilitates the conversion of Ga2O into GaN at high RF power of 2500 W, whereas O2 RPP mainly oxidizes GaN to relatively stable Ga2O3. Combined with the C–V and pulsed I–V measurements, it is confirmed that a strong positive correlation exists between Ga2O and the interface traps, rather than Ga2O3.

Temperature and frequency dependent dielectric capacitance and polarization performances of low dimensional perovskite based manganese stannate

Manganese stannate perovskite nanoparticles were synthesized by applying a complexation mediated approach. Rietveld refinement of the XRD data exhibited orthorhombic structure with space group of Pnma. The structure included eightfold coordinated Mn2+ cation, surrounded by eight O2− anions and formed MnO8 polyhedra unit. Each polyhedra unit interconnected through the corner-sharing SnO6 octahedra with the formation of a cage-like network. The temperature and frequency dependent dielectric performances of manganese stannate were measured in the form of a device, which exhibited maximum dielectric constant value ~ 3445. The high dielectric constant value was originated due to the contribution of space charge polarization and orientation polarization of dipoles within the measured frequency ranges. Temperature and frequency dependent AC-conduction mechanism of the manganese stannate-based device involved both overlapping large polarons and non-overlapping small polarons. Electric field-dependent of polarization hysteresis loop of the device exhibited the maximum polarization value 1.5 µC/cm2 under the electric field of 3 kV/mm. Under the applied field of 2 kV/mm, the device exhibited a fatigue-free polarization with a maximum value of 0.92 µC/cm2, sustained for 103 cycles under ambient temperature condition.

Differential outcomes of high-fat diet on age-related rescaling of cochlear frequency place coding.

Auditory frequency coding is place-specific, which depends on the mechanical coupling of the basilar membrane-outer hair cell (OHC)-tectorial membrane network. Prestin-based OHC electromotility improves cochlear frequency selectivity and sensitivity. Cochlear amplification determines the frequency coding wherein discrete sound frequencies find a 'best' place along the cochlear length. Loss of OHC is the leading cause of age-related hearing loss (ARHL) and is the most common cause of sensorineural hearing loss and compromised speech perception. Lipid interaction with Prestin impacts OHC function. It has been established that high-fat diet (HFD) is associated with ARHL. To determine whether genetic background and metabolism preserve cochlear frequency place coding, we examined the effect of HFD in C57BL/6J (B6) and CBA/CaJ (CBA) on ARHL.We found a significant rescuing effect on ARHL in aged B6 HFD cohort. Prestin levels and cell sizes were better maintained in the experimental B6-HFD group. We also found that distortion product otoacoustic emission (DPOAE) group delay measurement was preserved, which suggested stable frequency place coding. In contrast, the response to HFD in the CBA cohort was modest with no appreciable benefit to hearing threshold. Notably, group delay was shortened with age along with the control. In addition, the frequency dependent OHC nonlinear capacitance gradient was most pronounced at young age but decreased with age. Cochlear RNA-seq analysis revealed differential TRPV1 expression and lipid homeostasis. Activation of TRPV1 and downregulation of arachidonic acid led to downregulation of inflammatory response in B6 HFD, which protects the cochlea from ARHL. The genetic background and metabolic state-derived changes in OHC morphology and function collectively contribute to a redefined cochlear frequency place coding and improved age-related pitch perception.

(Invited) Numerical Simulation of Ohmic Impedance

Impedance spectroscopy measurements are often confounded by high-frequency phenomena associated with frequency-dependent ohmic resistance. Newman introduced the concept of frequency dispersion to account for the effect of the disk electrode geometry on the impedance response [1]. The phenomenon described by Newman in terms of frequency-dependent capacitance and ohmic resistance may be considered as an ohmic impedance, a transfer function associated with the resistance of the electrolyte to passage of current under the influence of geometry-induced (and frequency-dependent) non-uniform current and potential distributions [2].Two kinds of models are described in the presentation. Finite-element models account for the influence of geometry on the impedance response for a disk electrode. These models demonstrate the ohmic impedance. The second model is an interpretation model used to extract properties from impedance data. For most cases, data are truncated to avoid being confounded by ohmic impedance. On rare instances, the ohmic impedance may be extracted by regression to data.Gharbi et al. [3] suggested that the ohmic impedance follows the form of the Havriliak-Negami equation. The Havriliak-Negami equation was found to provide a good fit to the ohmic impedance calculated for different electrode geometries, including interdigitated electrodes [4] as well as disk electrodes [3].The ohmic impedance was obtained by Levenberg-Marquardt regression of a process model that accounted for the ohmic impedance [5]. The experiments were performed using ferri/ferrocyanide redox species (10 mM each) in a 0.5 M KCl solution. The working electrode consisted of a 5-mm-diameter Au disk rotating at 800 rpm. A Pt gauze (4 cm2) was used as the counterelectrode, a saturated Ag/AgCl electrode was used as a reference electrode, and the temperature of double-walled electrochemical cell was held at 25 ±0.1°C.The process model was expressed in terms of an ohmic impedance and an expression that accounted for the influence of a local constant-phase element on the faradaic reaction and the convective diffusion impedance, expressed in terms of a series expansion following the work of Tribollet and Newman [6]. Regressions were weighted by the experimentally determined error structure of the data, and the resulting parameters characteristic of the ohmic impedance were in excellent agreement with numerical simulations.References J. S. Newman, J. Electrochem. Soc., 117 (1970), 198.V. Huang, V. Vivier, M. E. Orazem, N. Pébère, and B. Tribollet, J. Electrochem. Soc., 154 (2007), C81-C88.O. Gharbi, A. Dizon, M. E. Orazem, M. T.T. Tran, B. Tribollet, and V. Vivier, Electrochim. Acta, 320 (2019), 134609.A. Dizon and M. E. Orazem, Electrochim. Acta, 337 (2019), 135000.W. Watson and M. E. Orazem, EIS: Measurement Model Program, ECSArXiv, 2020, https://ecsarxiv.org/kze9x/.B. Tribollet and J. S. Newman, J. Electrochem. Soc., 130 (1983), 2016.

Signal Integrity Analysis of Through-Silicon Via (TSV) With a Silicon Dioxide Well to Reduce Leakage Current for High-Bandwidth Memory Interface

In this paper, we propose and analyze a through silicon via (TSV) with a silicon dioxide well (SDW) to reduce leakage current in the design of a high-speed signaling and low-power consumption high-bandwidth memory (HBM) interface. In the proposed TSV, the SDW is inserted into the silicon substrate area between TSVs. By inserting the SDW, the silicon substrate’s effective conductivity and permittivity are lowered compared to a conventional TSV. The proposed TSV with the SDW improves insertion loss by up to 0.079 dB at 4 GHz by minimizing the leakage current. In addition, by reducing the effective permittivity of the silicon substrate, the difference in ratio between the capacitive coupling and inductive coupling is minimized. It is also possible to obtain a reduction in far-end crosstalk (FEXT) in the range of HBM interface signaling. RLGC modeling of the proposed TSV with the SDW is presented, and is physically analyzed based on the frequency-dependent equivalent capacitance and conductance of the silicon substrate. The proposed TSV with SDW is finally evaluated using an eye diagram, and the eye height and width improved by up to 13.7 % and 4.7 % at 8 Gb/s, respectively, compared to the conventional TSV. The proposed TSV also reduced dynamic power consumption by 48.1 % at 8 Gb/s, verifying the low-power structure.

Molecular p-doping induced dielectric constant increase of polythiophene films determined by impedance spectroscopy

The dielectric constant (εr) is a fundamental material parameter that governs charge transfer processes in organic semiconductors, yet its value is often assumed rather than measured. Here, we use impedance spectroscopy to determine εr in regioregular poly(3-hexylthiophen-2,5-diyl) (P3HT) thin films p-doped with the molecular dopants hexafluoro-tetracyanonaphthoquinodimethane and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). We fit the impedance spectra using a single RC circuit model to determine the frequency-dependent capacitance and extract εr. The value of the dielectric constant increases by around two-thirds from 2.9 ± 0.1 (undoped polymer) to 4.9 ± 0.6 on the addition of one F4TCNQ molecule per 500 P3HT monomer units. In contrast, the addition of the weak dopant 7,7,8,8-tetracyanoquinodimethane (TCNQ), which does not undergo ground state charge transfer with P3HT, has no effect on the dielectric constant. Our results support the hypothesis that molecular doping has a considerable impact on the materials dielectric constant via polarizable host-dopant complexes.

Synaptic Transistors Based on PVA: Chitosan Biopolymer Blended Electric-Double-Layer with High Ionic Conductivity.

This study proposed a biocompatible polymeric organic material-based synaptic transistor gated with a biopolymer electrolyte. A polyvinyl alcohol (PVA):chitosan (CS) biopolymer blended electrolyte with high ionic conductivity was used as an electrical double layer (EDL). It served as a gate insulator with a key function as an artificial synaptic transistor. The frequency-dependent capacitance characteristics of PVA:CS-based biopolymer EDL were evaluated using an EDL capacitor (Al/PVA: CS blended electrolyte-based EDL/Pt configuration). Consequently, the PVA:CS blended electrolyte behaved as an EDL owing to high capacitance (1.53 µF/cm2) at 100 Hz and internal mobile protonic ions. Electronic synaptic transistors fabricated using the PVA:CS blended electrolyte-based EDL membrane demonstrated basic artificial synaptic behaviors such as excitatory post-synaptic current modulation, paired-pulse facilitation, and dynamic signal-filtering functions by pre-synaptic spikes. In addition, the spike-timing-dependent plasticity was evaluated using synaptic spikes. The synaptic weight modulation was stable during repetitive spike cycles for potentiation and depression. Pattern recognition was conducted through a learning simulation for artificial neural networks (ANNs) using Modified National Institute of Standards and Technology datasheets to examine the neuromorphic computing system capability (high recognition rate of 92%). Therefore, the proposed synaptic transistor is suitable for ANNs and shows potential for biological and eco-friendly neuromorphic systems.

Investigating defects in InGaN based optoelectronics: from material and device perspective

III-nitride optoelectronics have revolutionized solid-state lighting technology. However, non-radiative defects play a major bottleneck in determining the performance of InGaN-based optoelectronics devices. It becomes especially challenging when high indium is required to be incorporated to obtain emission at higher wavelength (>500 nm). In this research article, we are going to discuss our investigation on the origin of defects in InGaN-based optoelectronics devices from the material and device perspective and characterize them through various techniques. This article broadly consists of two parts. In the first part, we investigate defects in InGaN based optoelectronics from a material point of view. Here, we discuss the challenges in the growth of InGaN planar (2-dimensional) and nanowires (1-dimensional) with high indium (≥20%) incorporation using the plasma-assisted molecular beam epitaxy (PA-MBE) technique. Photoluminescence spectroscopy (PL) has been performed to characterize these grown samples to assess their optical quality. Atomic force microscopy (AFM) has been employed to characterize the surface morphology of grown InGaN layers. High-resolution transmission electron microscopy (HRTEM) and scanning electron microcopy (SEM) are also used to characterize InGaN planar and nanowire samples grown under various process conditions. In the second part, we investigate the role of defects on InGaN optoelectronics from a device point of view. Here, we discuss the fabrication of InGaN multi-quantum well-based light emitting diodes (LEDs). Temperature-dependent current versus voltage measurements are carried out to investigate the role of defects on carrier dynamics under forward and reverse bias conditions. Frequency-dependent capacitance versus voltage (CV) and conductance versus voltage (GV) techniques are employed extensively to characterize defects in fabricated InGaN LEDs.

Theoretical Study for Carrier Transit Limited Performance of Gate-All-Around Si Nanowire Transistor by Time-Dependent Quantum Transport Simulation

Theoretically, the upper limit performance of nanoscale transistor should be limited by carrier transit time through the channel as the charge in channel cannot follow the gate voltage and the gate capacitance will show strong frequency dependence if the gate voltage varies faster than the carrier transit time. Currently, the operation frequency of nanoscale transistor is limited by the non-ideal factors such as parasitic effects, and it is far below the limit caused by carrier transit time. However, how good the transistor can be if one can minimize these non-ideal factors is still a problem, thus, it would be worth exploring its upper limit performance. In this article, time-dependent quantum transport simulation is performed to explore the carrier transit limited performance of the gate-all-around (GAA) Si nanowire transistor. By using the mode space approach, the 3-D time-dependent quantum transport equation is decoupled to a 2-D confinement problem and a 1-D transport problem, and then self-consistently solved with the Poisson’s equation. The transient characteristics of channel charge are investigated, and it shows the response time of channel charge is in the scale of 0.1 ps. The responses of channel charge and drain current to high-frequency gate voltages are simulated. The carrier transit limited performance including the frequency-dependent gate capacitance and transconductance, 3 dB bandwidth, and cutoff frequency, are calculated and discussed.

Flow control using single dielectric barrier discharge plasma actuator for flow over airfoil

The single dielectric barrier discharge (SDBD) plasma actuator has been developed in the present work for high-accuracy, high-performance computing of flow control applications. The present physics-based SDBD model is a significant improvement over the one developed by Bagade et al., [“Frequency-dependent capacitance–based plasma model for direct simulation of Navier–Stokes equation,” AIAA J. 55, 180–194 (2017)], which was used for planar geometry using sequential computation. Based on the physics of SDBD operation, phase-averaged fully developed body force over an ac cycle is computed and stored, which is reused. Thus, the intensive body force computations are bypassed in the new model, and the body force due to the SDBD plasma actuator is incorporated in the compressible Navier–Stokes equation that is solved in a body-fitted curvilinear coordinates. Here, the modified SDBD model enables performing large-scale simulations for the aerodynamic flow control at low speed and transonic flow past airfoils used in unmanned aerial vehicles and executive jets. The flow control by SDBD plasma actuation is finally compared with other forms of flow control strategies.

MBE-Grown Hybrid Axial Core–Shell n-i-p GaAsSb Heterojunction Ensemble Nanowire-Based Near-Infrared Photodetectors up to 1.5 μm

In this paper, high-performance self-assisted molecular beam epitaxy (MBE)-grown conventional core–shell (C–S) n-i-p GaAsSb nanowires (NWs) and a novel hybrid axial C–S n-i-p GaAsSb ensemble NW-based near-infrared photodetector (NIRPD) on nonpatterned Si substrate are demonstrated. The conventional room-temperature (RT) C–S n-i-p GaAsSb NW with a high responsivity of 190 A/W and a higher detectivity of 1.1 × 1014 Jones at −1 V bias and wavelength of 1.1 μm is reported by optimizing the intrinsic region thickness and appropriately compensating the intrinsic p-type behavior with n-dopant Te. Furthermore, hybrid axial C–S n-i-p GaAsSb has been band-gap-engineered for wavelength up to 1.5 μm, exhibiting responsivity of 18 A/W and detectivity of 1.1 × 1013 Jones operating at RT. In this hybrid design, we have combined both axial and radial intrinsic (i-) segments of different Sb% compositions to enhance the photoabsorption in the NIR region; hence, the photogenerated current and also the high-band-gap axial i-region help to suppress the trap-assisted tunneling mechanism, which is found to be advantageous over conventional C–S NW architectures. In addition, high rectification ratio from current–voltage (I–V) measurements, suppression of low-frequency noise, lack of 1/f noise, a low corner frequency of ∼2.5 Hz beyond which there is the presence of only frequency-independent white noise from low-frequency noise (LFN) measurements, and bias- and frequency-dependent capacitance–voltage (C–V) measurements suggest the formation of a high-quality C–S junction in the hybrid structure. Thus, our findings reveal that the hybrid axial C–S NW architecture provides the flexibility of three-dimensional (3D) design, which offers an unprecedented prospect for expanding IRPD and other next-generation optoelectronic device applications.