Depletion Region Research Articles

Si-ring quantum-well GAA nanowire FET for 5nm CMOS integration

Short-channel effects are a series of phenomena that take place when the channel length of the MOSFET becomes approximately equal to the space charge regions of source and drain junctions with the substrate. They lead to a series of issues including polysilicon gate depletion effect, threshold voltage rolloff, drain- induced barrier lowering (DIBL), velocity saturation, reverse leakage current rise, mobility reduction, hot carrier effects, and similar other annoyances in 5nm scale of transistor. So, to overcome the short- channel effects, gate leakage, and increased variability various methods have been proposed in order to improve the performance of these devices, including the use of materials with high carrier mobility such as germanium or III–V materials, multi gate transistors, tunneling FET (TFET) structures, and structure quantum wells, any of which can significantly reduce SCE (short channel effect).In this paper Si-ring GAA NW FET has proposed due to it has lower static leakage current and a smaller subthreshold slope than conventional MOSFET and GAA, and a good level of electrostatic control is created in the channel due to the channel being surrounded by the cylindrical gate. The performance of the device and its electrical characteristics have been determined using sentaurus TCAD.

O-band membrane photodetector with InGaAsP-bulk absorption core using Franz-Keldysh effect.

There has been an increasing need for small, low-cost, and low-power consumption optical transceivers for short-reach fiber links. Waveguide-integrated photodetectors (PDs) with wide bandwidth and high responsivity on Si photonics platforms are an essential element for these applications. We have fabricated an O-band membrane PD which is suitable for integration with high-performance III-V-based membrane devices such as lasers and modulators, and passive waveguide circuits on the Si photonics platforms. The membrane PD consists of an InGaAsP-bulk absorption core embedded with an InP-based lateral p-i-n junction. The width of the InGaAsP absorption core is designed to be 350 nm and the doped regions overlap with the edges of the core to reduce the carrier transit time. In the structure, however, photocarriers generated in the doped core appear to be a limiting factor of the operating speed since the photocarriers diffuse into the depletion region with a long time constant. To avoid this, we design the bandgap wavelength of the absorption core to be shorter than the operating wavelength. As the electric field is mainly applied to the undoped InGaAsP absorption core region when the reverse bias is applied to the PD, the absorption coefficient in the undoped core region increases due to Franz-Keldysh effect (FKE) while the doped regions maintain a low absorption coefficient due to the wavelength detuning. A membrane PD with an absorption length of 30 µm integrated with the SiOx waveguide was fabricated by using a heterogeneous integration technique on a Si photonics platform. We verified that the FKE causes the photocurrent to increase. In addition, the OE bandwidth was observed to increase due to the wavelength detuning. The fabricated PD exhibited a fiber-to-PD responsivity of 0.6 A/W and a bandwidth over 67 GHz. Eye openings for 100-Gbit/s NRZ signals were demonstrated at a stage temperature of 25°C.

Enhanced Short-Circuit Robustness of 1.2 kV Split Gate Silicon Carbide Metal Oxide Semiconductor Field-Effect Transistors for High-Frequency Applications

Split Gate SiC MOSFETs (SG-MOSFETs) have been demonstrated to exhibit excellent power dissipation at high operating frequencies due to their low specific reverse transfer capacitance (Crss,sp); however, there are several reliability issues of SG-MOSFETs, including electric field crowding at the gate oxide and insufficient short-circuit (SC) robustness. In this paper, we propose a device structure to enhance the short-circuit withstand time (SCWT) of 1.2 kV SG-MOSFETs. The proposed P-shielded SG-MOSFETs (PSG-MOSFETs) feature a P-shielding region that expands the depletion region within the JFET region under both blocking mode and SC conditions. Compared to the conventional structure, this reduces the maximum electric field in the gate oxide, enabling a higher doping concentration in the JFET region, which can reduce the specific on-resistance (Ron,sp) to minimize power dissipation during device operation. The SC robustness of PSG-MOSFETs, with an Ron,sp identical to those of SG-MOSFETs, was investigated by adjusting the width of the P-shielding region (WP). Furthermore, the Crss,sp of PSG-MOSFETs was compared with that of SG-MOSFETs to analyze the relationship between the WP and high-frequency figure of merit (HF-FOM), defined as Ron,sp × Crss,sp. These results demonstrated that the PSG-MOSFET achieved an enhanced SC robustness and HF-FOM in comparison to the SG-MOSFET. Thus, the proposed PSG-MOSFET is a highly suitable candidate for high-frequency and reliable applications.

Quantification of mobile charge carrier yield and transport lengths in ultrathin film light-trapping ZnFe2O4 photoanodes.

Zinc ferrite (ZnFe2O4, ZFO) has gained attention as a candidate material for photoelectrochemical water oxidation. However, champion devices have achieved photocurrents far below that predicted by its bandgap energy. Herein, strong optical interference is employed in compact ultrathin film (8-14 nm) Ti-doped ZFO films deposited on specular back reflectors to boost photoanode performance through enhanced light trapping, resulting in a roughly fourfold improvement in absorption as compared to films deposited on transparent substrates. The spatial charge carrier collection profile and wavelength-dependent photogeneration yield of mobile charge carriers was then extracted via spatial collection efficiency analysis based on optical and external quantum efficiency measurements. We demonstrate that despite the enhanced performance enabled by the light trapping structure, substantial recombination occurs for thin film ZFO photoanodes even within the space charge region of an ultrathin film photoanode. Furthermore, the excitation-wavelength-dependent yield of mobile charge carriers in ZFO is shown to be less than unity across the visible spectrum, ultimately limiting the attainable photocurrent density. These results explain the underperformance of ZFO as a photoanode material and suggest that reduction of the mobile charge carrier yield due to the existence of ligand field states is a dominant loss mechanism for metal-oxides containing Fe metal centers with open d-shell configuration.

PbS@NiFe-LDH heterojunction: an efficient photo-assisted electrocatalyst for the OER.

Recently, photo-assisted electrocatalysis as an emerging catalytic approach that combines the technologies of photocatalysis and electrocatalysis has attracted great interest among researchers. Under this circumstance, the NiFe-LDH compounded with PbS based (PbS@NFHS) heterojunction with both photoactive and electrocatalytic properties was constructed for the first time through an ambient etching route and a subsequent low-temperature hydrothermal method. The as-prepared catalyst displayed a novel hierarchical 3D open structure based on nanosheets, which offered numerous electrochemically active sites, facilitated the swift diffusion of ions and enhanced both electrical conductivity and catalytic stability, thus significantly improving the catalytic performance. Furthermore, the charge redistribution in the p-n junction led to the formation of space-charge regions and a built-in electric field, which benefited the charge transfer and thereby enhanced the intrinsic activity. Under illumination, electrochemical tests showed that the overpotential was only 291 mV for the OER at 50 mA cm-2 in 1 M KOH solution, which was 50 mV lower than that without illumination. Moreover, the catalyst can maintain stability for 40 hours at a current of 10 mA cm-2 in 1 M KOH. Compared to the traditional electrocatalytic OER, this work employed a very promising photo-assisted electrocatalytic strategy, which could further broaden the wide application of NiFe-LDH.

Built-in electric field in the Mn/C60 heterojunction promotes electrocatalytic nitrogen reduction to ammonia.

The electrochemical nitrogen reduction reaction (NRR) has been regarded as a green and promising alternative to the traditional Haber-Bosch process. However, the high bond energy (940.95 kJ mol-1) of the NN triple bond hinders the adsorption and activation of N2 molecules, which is a critical factor restricting the catalytic performance of catalysts and their large-scale applications. Herein, an Mn/C60 heterostructure is constructed via a simple grinding and calcination process and achieves an extraordinary faradaic efficiency of 42.18% and an NH3 yield rate of 14.52 μg h-1 mgcat-1 at -0.4 V vs. RHE in 0.08 M Na2HPO4. Our experimental and theoretical results solidly confirm that the spontaneous charge transfer at the Mn/C60 heterointerface promotes the formation of a built-in electric field, which facilitates the electron transfer from Mn towards C60 and creates localized electrophilic and nucleophilic regions. The formation of the space-charge region effectively optimized the adsorption energy of the key intermediate *NH-*NH2 and also reduced the free energy barrier for the hydrogenation step of *NH-*NH to *NH-*NH2. Furthermore, the calculated lower limiting potential (UL(NRR)) in Mn/C60 relative to the HER (UL(HER)) demonstrates its enhanced selectivity toward the NRR. This work provided new insights into enhancing the activity and performance of electrocatalysts for the NRR by constructing heterojunctions to improve nitrogen adsorption.

Rational electronic structure modulation in the space-charge region of α-Co(OH)2/CeO2 p-n heterojunction to boost hydrogen evolution reaction

Rational electronic structure modulation in the space-charge region of α-Co(OH)2/CeO2 p-n heterojunction to boost hydrogen evolution reaction

A Review of Research on Potential Solutions for Dendrite Growth in Solid State Cells

The formation of lithium dendrites can lead to irreversible capacity loss and pose safety risks in lithium batteries. One proposed model suggests that when the current density is too high, a depletion layer of lithium ions forms near the anode, promoting dendrite growth. Lithium dendrites may puncture the membrane of the battery and reach the positive electrode, causing the battery to short circuit, causing the battery to overheat and possibly explode. This growth can result in short circuits in conventional lithium batteries. Several strategies can be employed to inhibit the growth of lithium dendrites. These include coating the lithium metal surface with durable layers or alloy compounds, micro-modulating the solid-state electrolyte to reduce dendrite nucleation, and managing nano-cracks in the electrolyte. These approaches have shown promising results in enhancing the stability and cycling performance of lithium metal anodes. However, technological constraints still limit the widespread implementation of these strategies, and more advanced characterization techniques are needed to better understand and address the issue of dendrite growth in solid-state batteries.

Ion concentration polarization causes a nearly pore-length-independent conductance of nanopores.

There has been a great amount of interest in nanopores as the basis for sensors and templates for preparation of biomimetic channels as well as model systems to understand transport properties at the nanoscale. The presence of surface charges on the pore walls has been shown to induce ion selectivity as well as enhance ionic conductance compared to uncharged pores. Here, using three-dimensional continuum modeling, we examine the role of the length of charged nanopores as well as applied voltage for controlling ion selectivity and ionic conductance of single nanopores and small nanopore arrays. First, we present conditions where the ion current and ion selectivity of nanopores with homogeneous surface charges remain unchanged, even if the pore length decreases by a factor of 6. This length-independent conductance is explained through the effect of ion concentration polarization (ICP), which modifies local ionic concentrations, not only at the pore entrances but also in the pore in a voltage-dependent manner. We describe how voltage controls the ion selectivity of nanopores with different lengths and present the conditions when charged nanopores conduct less current than uncharged pores of the same geometrical characteristics. The manuscript provides different measures of the extent of the depletion zone induced by ICP in single pores and nanopore arrays, including systems with ionic diodes. The modeling shown here will help design selective nanopores for a variety of applications where single nanopores and nanopore arrays are used.

The investigation of main electrical parameters, energy dependent profiles of surface states and their lifetimes in the Au/n-Si Schottky diodes with (PVA-Fe3O4) interlayer depend on frequency and voltage

Abstract In this article, the impedance-voltage-frequency (Z-V-f) measurements of the fabricated Au/(PVA-Fe3O4)/n-Si SDs have been performed between 0.1 kHz and 1 MHz, and in the ±3 V range. Main important electronic parameters of the Schottky diode (SD) like diffusion - potential (VD), Fermi - energy (EF), barrier - height (ΦB), depletion layer (WD), and max. electric field (Em) were extracted from the reverse bias 1/C2 - V plots in a wide frequency range. The voltage-reliant variations of the surface states (Nss) have been calculated by using low—high frequency capacitance (CLF-CHF), and parallel conductance or admittance models and compared to each other. The voltage-reliant resistance profile of Ri has also been obtained from the Nicollian & Brews method for all frequencies. All these results indicate that these main electrical parameters are strongly dependent on voltage and frequency due to the existence of Nss, their lifetimes (τ), interfacial organic layer, Rs, interface, and dipole polarizations. But, while Nss is effective, both in depletion and inversion regions, Rs is dominant at the strong-accumulation region at high enough frequency.

Analytical Solutions and Computer Modeling of a Boundary Value Problem for a Nonstationary System of Nernst–Planck–Poisson Equations in a Diffusion Layer

This article proposes various new approximate analytical solutions of the boundary value problem for the non-stationary system of Nernst–Planck–Poisson (NPP) equations in the diffusion layer of an ideally selective ion-exchange membrane at overlimiting current densities. As is known, the diffusion layer in the general case consists of a space charge region and a region of local electroneutrality. The proposed analytical solutions of the boundary value problems for the non-stationary system of Nernst–Planck–Poisson equations are based on the derivation of a new singularly perturbed nonlinear partial differential equation for the potential in the space charge region (SCR). This equation can be reduced to a singularly perturbed inhomogeneous Burgers equation, which, by the Hopf–Cole transformation, is reduced to an inhomogeneous singularly perturbed linear equation of parabolic type. Inside the extended SCR, there is a sufficiently accurate analytical approximation to the solution of the original boundary value problem. The electroneutrality region has a curvilinear boundary with the SCR, and with an unknown boundary condition on it. The article proposes a solution to this problem. The new analytical solution methods developed in the article can be used to study non-stationary boundary value problems of salt ion transfer in membrane systems. The new analytical solution methods developed in the article can be used to study non-stationary boundary value problems of salt ion transport in membrane systems.

High Current Gain MoS2 Bipolar Junction Transistor Based on Metal-Semiconductor Schottky Contacts.

Bipolar junction transistors (BJTs) are crucial components in high-power electronic applications. However, while two-dimensional (2D) semiconductors with exceptional electrical properties have been extensively studied in field-effect transistors, their application in BJTs has received far less attention. In this study, we demonstrate high-gain MoS2 BJTs based on metal-semiconductor Schottky contacts. The emitter-base junction uses the thermal ionization properties of a Schottky diode to emit electrons, while the collector-base junction leverages the Schottky barrier to collect electrons. This design enables thermal ionization of electrons into the base region, where they are subsequently accelerated and transferred to the collector region under the influence of the collector-base junction voltage. Our MoS2 BJTs achieves a common-base current gain 0.99 and a remarkable common-emitter current gain of 1967, representing the highest performance reported for BJTs based on 2D semiconductors to date, which is comparable to traditional silicon-based BJTs.

Influence of Varying Recessed Gate Height on Analog/RF Performances of a Novel Normally-Off Underlapped Double Gate AlGaN/GaN-based MOS-HEMT

Current transistor technology has issues with off-state current which reduces power efficiency. The paper presents a novel Normally-off Underlapped Dual Gate (U-DG) AlGaN/GaN MOS-HEMT device to tackle these issues. A novel dual recessed gate technology is implemented in the device which deepens the depletion region, creating a strong barrier that prevents current flow at negative gate voltage. The study investigates various recessed gate heights’ impact on analog and RF performance. Key parameters like drain and gate Currents, transconductance, and transconductance generation factor were analyzed, alongside intrinsic capacitance, gate capacitance, intrinsic resistance and maximum oscillation frequency. Results indicate that a 19 nm recessed gate height offers optimal performance. It is the only one to achieve a normally off state and a substantial 45% increase in transconductance compared to other heights. This research provides crucial insights into designing efficient Normally-off U-DG AlGaN/GaN MOS-HEMT devices, particularly relevant for low-power applications.

Influence of the nature of the distribution of recombination centers in the space charge region of the p–n junction on the parameters of the current–voltage characteristics within the classical Shockley and Shockley–Noyce–Sah models

Abstract The behavior of current–voltage characteristics (CVC) within the classical Shockley and Shockley–Noyce–Sah models depending on the nature of the distribution of recombination centers in the space charge region of the p–n junction was analyzed. Notably, the non-ideality factor determined from experimental CVC cannot be introduced into the exponent of the mathematical model of the CVC because it is unrelated to the physical nature of the exponentials of classical models but indicates the voltage dependence of the pre-exponential factor of the recombination component of the total current. The exponential factor of the model with a non-ideality factor describing the experimental CVC presents only a mathematical approximation of a small portion of it.

Assessment on wire-arc additive manufactured high strength low alloy steel cylindrical component

Large structural parts are widely manufactured through wire-arc additive manufacturing (WAAM) due to its high deposition rate, flexibility, and low cost. There are a variety of industries where high strength low alloy (HSLA) steel is used, including naval, tool and die manufacturing, construction, and offshore structures. The present article examines the mechanical properties and microstructural evolution of a developed HSLA component. The microstructural analysis was done in the component’s top (TR) and bottom (BR) regions. It reveals almost similar microstructural constituents but with more polygonal ferrite in the TR and bainitic structure in the bottom, with acicular ferrite in both regions. The inclusions in both regions were characterized using energy-dispersive X-ray spectroscopy. This demonstrates that manganese (Mn), as a strong deoxidizer, reacts with oxygen and dissolves entirely within the inclusion, forming a Mn depletion zone. Additionally, grain coarsening was observed in the building direction. The average grain size in the TR and BR was 13.12 μm and 6.54 μm, respectively. Within the regions considered, only 2.47%, 4.06%, and 0.65% variations were observed between yield strength, ultimate tensile strength, and elongation to fracture.

Formation of All Tin Oxide p–n Junctions (SnO–SnO2) during Thermal Oxidation of Thin Sn Films

Metastable stannous oxide (SnO) phase of p‐type semiconductor and all tin oxides p–n junctions of SnO–SnO2 nanostructures are formed by controlled thermal oxidation of thin tin films. High purity Sn is deposited on quartz substrates using a vacuum‐assisted thermal evaporation technique. Afterwards, controlled thermal oxidation at different temperatures is performed in air ambient condition (150–800 °C). Various surface characterization techniques have been employed to analyze the structure, morphology, chemistry, optical, and electronic properties of these SnOx films. P‐type SnO phase is found to be thermodynamically stable at lower oxidation temperatures (250–400 °C), while n‐type SnO2 phase starts to appear above 500 °C. Highly uniform and dense SnO nanospheres along with few 1D nanorods are observed after oxidation at 400 °C. Mixed oxide phases of p–n junctions with a sudden decrease in electrical conductivity is observed for 500 °C film. Significantly lower surface conductivity of mixed oxide phase indicates the formation of depletion layers between p‐type SnO and n‐type SnO2 nanograins. A transition from SnO layer to SnO2 layer is also observed above 600 °C. Overall, SnOx‐based nanostructures would be a potential candidate for solar cells, p‐channel thin film transistors, p–n junction diodes and gas sensors.

Normally-Off Trench-Gated AlGaN/GaN Current Aperture Vertical Electron Transistor with Double Superjunction

This study proposes an AlGaN/GaN current aperture vertical electron transistor (CAVET) featuring a double superjunction (SJ) to enhance breakdown voltage (BV) and investigates its electrical characteristics via technology computer-aided design (TCAD) Silvaco Atlas simulation. An additional p-pillar was formed beneath the gate current blocking layer to create a lateral depletion region that provided a high off-state breakdown voltage. To address the tradeoff between the drain current and off-state breakdown voltage, the key design parameters were carefully optimized. The proposed device exhibited a higher off-state breakdown voltage (2933 V) than the device with a single SJ (2786 V), although the specific on-resistance of the proposed method (1.29 mΩ·cm−2) was slightly higher than that of the single SJ device (1.17 mΩ·cm−2). In addition, the reverse transfer capacitance was improved by 15.6% in the proposed device.

Reconfigurable Artificial Perception System and Logic Gates Based on Large‐Scale Antiambipolar 2D Heterostructure Array

AbstractVan der Waals (vdWs) heterostructures enable the fabrication of various optoelectronic devices with unprecedented functionalities, particularly antiambipolar transistors. Different methods have been employed to construct such devices; however, their integration and versatility remain significantly constrained. Here, large‐scale antiambipolar vdWs heterostructure arrays capable of implementing self‐adaptive artificial perception systems and reconfigurable logic gates are verified adopting 2D Te/WS2 heterojunctions for the first time. The resulting transistors allow the modulation of band slope and depletion regions in individual constituents through electrostatic gating, delivering a high rectification ratio of 1.8 × 104. Benefiting from the gate‐tunable antiambipolar characteristic and charge capture, such a device can realize reconfigurable modulation of synaptic plasticity between excitatory and inhibitory modes, enabling the emulation of artificial perception system for the adaptive and subjective perception adjustment in various external environments and also a recognition accuracy of 90.5% for image classification through training and inference simulations. In addition, five fundamental logic gate operations with good stability and reliability, as well as low energy consumption, are achieved in the dual‐gate antiambipolar transistor by tuning the input signals. Furthermore, similar antiambipolar characteristics are also observed from other 2D Te‐based heterostructures, defining a simple, effective, and universal method to create multifunctional antiambipolar transistors.

Improved photoresponse performance of self-powered solar-blind UV photodetectors based on n-Si/n-Ga2O3/p-Li:NiO dual-junction

The solar-blind photodetectors (SBPDs) based on the wide-bandgap semiconductor gallium oxide (Ga2O3) exhibit significant potential for applications in military, civilian, and medical fields. Although multiple structural designs of Ga2O3-based SBPDs have been proposed, their performance typically falls short of commercial standards. However, the photoresponse speed of most self-powered PDs decreases rapidly in the solar-blind region. To address this issue, we first prepared high-quality single-crystal β-Ga2O3 films using RF magnetron sputtering, which exhibit an average transmittance exceeding 85% across the 400–800 nm range and possess a relatively smooth surface. Subsequently, a superior performance self-powered SBPD of vertical structure of n-Si/n-Ga2O3/p-Li:NiO dual-junction was fabricated, which possesses a responsivity of 0.18 mA/W, a photo-to-dark current ratio of 395, rapid rise/decay times of 132/148 ms, and a specific detectivity of 1.57 × 109 Jones at 0 V bias under 254 nm illumination. The photocurrent of the device fully recovered to its initial level after experiencing changes in ambient temperature [from room temperature (RT) to 100 °C and back to RT], demonstrating robust stability in harsh environments. In addition, the valence band structures of p-Li:NiO and n-Ga2O3 were investigated in detail using XPS, and the working mechanism of the devices was analyzed based on the Fermi level alignment. The excellent performance of PDs can be attributed to the increased depletion layer width, which generates more photogenerated carriers. Additionally, the separation and transmission of photo-induced carriers are enhanced by the superposition of a double built-in electric field. Our strategy offers a promising approach for achieving high-performance Ga2O3-based photovoltaic PDs.

Calculation of the Efficiency of a Photodiode with Generation and Recombination in the Space-Charge Region

Calculation of the Efficiency of a Photodiode with Generation and Recombination in the Space-Charge Region