Depletion Region Research Articles

Development of Semi-Empirical and Machine Learning Models for Photoelectrochemical Cells

We introduce a theoretical model for the photocurrent-voltage (I-V) characteristics designed to elucidate the interfacial phenomena in photoelectrochemical cells (PECs). This model investigates the sources of voltage losses and the distribution of photocurrent across the semiconductor–electrolyte interface (SEI). It calculates the whole exchange current parameter to derive cell polarization data at the SEI and visualizes the potential drop across n-type cells. The I-V model’s simulation outcomes are utilized to distinguish between the impacts of bulk recombination and space charge region (SCR) recombination within semiconductor cells. Furthermore, we develop an advanced deep neural network model to analyze the electron–hole transfer dynamics using the I-V characteristic curve. The model’s robustness is evaluated and validated with real-time experimental data, demonstrating a high degree of concordance with observed results.

Constructing Quasi-Single Ion Conductors by a β-Cyclodextrin Polymer to Stabilize Zn Anode.

Aqueous Zn-ion batteries (AZIBs) are promising for the next-generation large-scale energy storage. However, the Zn anode remains facing challenges. Here, we report a cyclodextrin polymer (P-CD) to construct quasi-single ion conductor for coating and protecting Zn anodes. The P-CD coating layer inhibited the corrosion of Zn anode and prevented the side reaction of metal anodes. More important is that the cyclodextrin units enabled the trapping of anions through host-guest interactions and hydrogen bonds, forming a quasi-single ion conductor that elevated the Zn ion transference number (from 0.31 to 0.68), suppressed the formation of space charge regions and hence stabilized the plating/striping of Zn ions. As a result, the Zn//Zn symmetric cells coated with P-CD achieved a 70.6 times improvement in cycle life at high current densities of 10 mA cm-2 with 10 mAh cm-2. Importantly, the Zn//K1.1V3O8 (KVO) full-cells with high mass loading of cathode materials and low N/P ratio of 1.46 reached the capacity retention of 94.5 % after 1000 cycles at 10 A g-1; while the cell without coating failed only after 230 cycles. These results provide novel perspective into the control of solid-electrolyte interfaces for stabilizing Zn anode and offer a practical strategy to improve AZIBs.

Constructing Quasi‐Single Ion Conductors by a β‐Cyclodextrin Polymer to Stabilize Zn Anode

AbstractAqueous Zn‐ion batteries (AZIBs) are promising for the next‐generation large‐scale energy storage. However, the Zn anode remains facing challenges. Here, we report a cyclodextrin polymer (P‐CD) to construct quasi‐single ion conductor for coating and protecting Zn anodes. The P‐CD coating layer inhibited the corrosion of Zn anode and prevented the side reaction of metal anodes. More important is that the cyclodextrin units enabled the trapping of anions through host–guest interactions and hydrogen bonds, forming a quasi‐single ion conductor that elevated the Zn ion transference number (from 0.31 to 0.68), suppressed the formation of space charge regions and hence stabilized the plating/striping of Zn ions. As a result, the Zn//Zn symmetric cells coated with P‐CD achieved a 70.6 times improvement in cycle life at high current densities of 10 mA cm−2 with 10 mAh cm−2. Importantly, the Zn//K1.1V3O8 (KVO) full‐cells with high mass loading of cathode materials and low N/P ratio of 1.46 reached the capacity retention of 94.5 % after 1000 cycles at 10 A g−1; while the cell without coating failed only after 230 cycles. These results provide novel perspective into the control of solid‐electrolyte interfaces for stabilizing Zn anode and offer a practical strategy to improve AZIBs.

Circuit Modeling of the Impact of Heavy Charged Particles on Transient Processes in Bipolar Analog Microcircuits

One of the factors causing the failure of spacecraft integrated circuits is exposure to heavy charged particles. The entry of heavy charged particles into electronic devices leads to the appearance of single event transients (short current pulses), which in analog microcircuits manifest themselves in distortion of the output signal shape, and in digital microcircuits can cause a single event upset. The article discusses a technique for circuit mode-ling of the effect of heavy charged particles on bipolar analog microcircuits, including the developed equivalent electrical circuit of a bipolar transistor for LTSpice and the procedure for modeling transient processes. Despite the simplifications adopted, namely: failure to take into account the dependence of the duration of the rise and fall of the current pulse generated by a charged particle on the parameters of the transistor structure, the assumption that the entire charge is generated in the active base and the space charge regions of the emitter and collector junctions, an equivalent circuit has been developed made it possible to determine that the shape of the collector current pulse for circuit with a common emitter when exposed to a heavy charged particle is determined by the speed of the transistor and its operating mode. Using the developed methodology, the “critical” transistors of the two studied analog microcircuits were determined, and the need to bypass the current-setting resistors with a small capacitor was justified.

High-performance deep-ultraviolet photodetector based on a single-crystalline ϵ-Ga2O3/Sn-doped In2O3 heterojunction

Abstract Metastable ϵ-Ga2O3, with its superior physical properties and high substrate compatibility, demonstrates considerable potential in developing heterojunction deep-ultraviolet photodetectors (DUV PDs). Herein, we fabricate a high-performance DUV PD utilizing a single crystalline ϵ-Ga2O3/ Sn-doped In2O3 (ITO) heterojunction. Under a reverse bias of 15 V, the device exhibits a high responsivity of 506 A/W, an excellent UV/visible rejection ratio of 6.74 × 104, and a fast fall time of 40 ms while maintaining good performance across a broad illumination range of 90–4100 μW cm−2. Moreover, the device can operate in a self-powered mode at zero bias, further verifying the presence of a depletion region within the ϵ-Ga2O3/ITO heterojunction. Our results demonstrate that ϵ-Ga2O3 is promising for high-quality integration on ITO and application in DUV detection, offering new strategic directions for developing high-performance Ga2O3-based DUV PDs.

Fabrication of heterostructure multilayer devices through the optimization of Bi-metal sulfides for high-performance quantum dot-sensitized solar cells.

In this work, a titanium dioxide and lead sulfide (TiO2/PbS) nano-size heterostructure with tin sulfide was fabricated and coated via a two-step direct deposition process. Its microstructure, morphology, elemental composition, optical absorption, and photochemical activity were investigated. Linear sweep voltammetry and cyclic voltammetry curves substantiated its catalytic activity, indicating quantum dot effects of a well-developed space charge domain on the surface of the hybrid structure. These give rise to electron-hole recombination suppression and a high charge mobility rate. Moreover, direct stabilization was identified in current density, corresponding to the hybrid structures limiting the diffusion current process. Higher J SC values observed were substantiated by the role of quantum dot-size effects and enhanced crystalline structures, leading to a reduction in series resistance and an improved conversion efficiency of 10.05%. Overall, theoretical analyses and empirical findings indicated that the seamless migration of photoexcited electrons across the interfaces of SnS and PbS is linked to quantum dot effect synergy. This is facilitated by the space charge region, which serves as a conduit for efficient electron transfer between the respective materials.

Rational design of ZnO-SnO2 Janus nanofibers for highly sensitive triethylamine detection

Herein, ZnO-SnO2 Janus nanofibers (NFs) were synthesized by a parallel electrospinning method and its sensing performances were tested. Considering the compositions of the two metal oxide semiconductors in Janus structure, different ratios of ZnO and SnO2 were designed and controlled. The optimum ratios of ZnO and SnO2 was 1:2 by analyzing their sensing performances to triethylamine (TEA) gas. Gas sensors based on ZS-12 Janus NFs exhibited a high response to TEA (45.2) and an excellent sensing response/recovery reproducibility. In order to investigate the sensing mechanism of Janus structure, ZnO NFs and SnO2 NFs were synthesized and used as controlled experiment. The results indicated that the heterostructures in Janus NFs is the key factor for the enhanced TEA sensing performances. The electrons flowed in the ZnO-SnO2 Janus structure leading to the variation of ionic oxygen species and electron depletion layer. These phenomena improved the reaction of TEA gas molecules with ionic oxygen species so that the TEA sensing performances were enhanced. Based on the Janus structures, a satisfactory gas sensor for detecting TEA gas were developed. Significantly, this work investigated the sensing mechanism of Janus structures and provided an efficient strategy for the gas sensing materials.

Transient Current Analysis of GaN Neutron Detector Based on the SRIM and TCAD Methods

Utilizing Technology Computer Aided Design (TCAD) software, this study determines the optimal thickness and doping concentration for the intrinsic gallium nitride (GaN) layer in a p-i-n GaN diode to improve detection efficiency and reliability. The study examines energy loss and the transient current response induced by alpha and 3H particles within the GaN p-i-n diode. Additionally, TCAD elucidates the transient current behavior arising from electron-hole pair generation, utilizing the Stopping and Range of Ions in Matter SRIM-2013 linear energy transfer distribution as a guide. The simulations disclose that the tailing effect in the transient current response results from radiation-induced hole accumulation. Elevated applied bias results in increased transient current pulse amplitude, attributed to an extended depletion region that boosts carrier collection. These insights are expected to drive advancements in GaN-based neutron detector technology, essential for advancing nuclear and space science applications in the next generation.

Numerical optimization of inorganic p-Sb2Se3/n-ZrS2 heterojunction solar cells: achieving high efficiency through SCAPS-1D simulation

p-Sb2Se3 and n-ZrS2 materials show strong potential for cost-effective photovoltaic applications. This study presents a detailed numerical analysis of p-Sb2Se3/n-ZrS2 heterojunction solar cells using SCAPS-1D, focusing on how key parameters such as layer thickness, doping density, and bandgap have affected device performance. Critical photovoltaic metrics, such as built-in voltage (Vbi), carrier lifetime, depletion width (Wd), recombination rates, and photogenerated current, were examined. Our findings demonstrate that optimizing the p-Sb2Se3 absorber layer with a 1.0 eV bandgap, 5000 nm thickness, and doping density of 1020 cm−3 leads to a maximum efficiency of 32.14%, with a fill factor (FF) of 84.57%, short-circuit current density (Jsc) of 47.61 mA cm−2, and open-circuit voltage (Voc) of 0.792 V. For the ZrS2 buffer layer, the best performance was achieved with a 1.2 eV bandgap, 200 nm thickness, and doping density below 1 × 1020 cm−3. These optimized parameters significantly enhanced carrier separation and minimized recombination losses, leading to improved power conversion efficiency. In addition to theoretical optimization, this study emphasizes the practical potential of these materials for real-world applications. The combination of Sb2Se3 and ZrS2 offers a low-cost fabrication process suitable for scalable commercial solar cell production while maintaining high efficiency. These results underscore the viability of p-Sb2Se3/n-ZrS2 heterojunctions as promising candidates for next-generation clean energy solutions.

Bipolar Membranes Via Divergent Synthesis: On the Interplay between Ion Exchange Capacity and Water Dissociation Catalysis.

Bipolar membranes (BPMs) enable the operation of electrochemical reactors with electrode compartments in different chemical environments or pH. The transport properties at the microscopic scale are dictated by the composition and morphology of the interfacial junctions as well as the specific chemistry of the ion-exchange layers that support the current of protons and hydroxide ions. This work elucidates the relation between water-dissociation efficiency and the physicochemical properties of the individual ion-exchange membrane layers in the poly(styrene-b-poly(ethylene-ran-butylene)-b-polystyrene) (SEBS)-based BPM. The optimal water dissociation performance of three previously reported water-dissociation catalysts in the SEBS-based BPM was examined, with junction thickness of graphene oxide > TiO2 > SnO2, resulting in disparate junction morphologies at the BPM's interface. A hybrid junction system, which included both the effective water dissociation catalyst SnO2 and direct contacting of the ion-exchange membrane layer, exhibited high water dissociation efficiency. This was likely due to the immediate ion transport pathway provided by direct membrane contact around the catalyst, which also improved the interfacial adhesion. A higher ion exchange capacity (IEC) in BPMs substantially enhanced the water dissociation performance in BPMs without water-dissociation catalysts. However, the incorporation of the effective SnO2 catalyst into the BPMs with a lower IEC significantly improved performance, an effect attributed to the hybrid junction system. Additionally, the increase in water uptake and ion conductivity of the cation exchange layer with higher IEC suggested that the cation exchange layer and its interface to the water-dissociation catalyst layer may play a key role in water dissociation. This study identifies the key parameters of individual BPM components and their interactions to water dissociation performance, offering new insights to guide in the construction of future BPMs optimized for enhanced water dissociation efficiency at high current densities.

High‐Gain and Tunable Linear Photodetection in 2D Tunneling Heterostructures Through Potential Engineering

Abstract2D materials are extensively employed in the fabrication of high‐performance photodetectors owing to their exceptional physical properties. However, most 2D material photodetectors fail to sustain high gain under intense illumination due to the limited intrinsic trap states. Here, an n‐n type Bi2O2Se/SnSe2 van der Waals tunneling heterojunction photodetector with a detection range from visible to near‐infrared (VIS‐NIR) is presented. Under reverse bias, the heterojunction induces a significant electron barrier and hole potential well, ensuring low leakage current and ample hole defect states. Therefore, the photodetector demonstrated a responsivity of 1636.3 AW−1 and a detectivity of 1.39 × 1014 Jones under 660 nm illumination, maintaining a tunable linear dynamic range (LDR) of ≈74.7 dB. This performance is attributed to the hole potential well‐suppressing the recombination of photogenerated carriers, thereby enhancing the device's gain. Furthermore, the tunneling of photogenerated electrons within the heterojunction's space charge region under bias enables rapid response (75.1 and 15.6 µs). In summary, the study introduces a novel strategy to overcome the limited detection capabilities of 2D devices under intense illumination, characterized by outstanding linearity for rapid detection and high‐resolution imaging.

Increasing the Efficiency of Thermoelectric Conversion of Solar Energy

The article considers the latest achievements in the field of thermionic conversion of solar energy. The key aspects of thermionic emission, the problems of reducing the electrode work function and increasing the efficiency of devices are analyzed. It is shown that diamonds doped with phosphorus can be an attractive material for the purposes of thermionic emission. In this case, the presence of donor states can significantly narrow the space charge region, and at the same time reduce the potential barrier in the work function. The studies also found that the most successful and widely used method for overcoming the space charge effect is filling the interelectrode gap with cesium. The efficiency of thermionic conversion devices for solar energy increases by 1.6 times. Particular attention is paid to the use of new materials, such as nanostructures and carbon nanotubes, as well as promising technologies, such as photonic enhancement of thermionic processes. The analysis of the results showed that the photonic enhancement of the electron yield due to illumination is greater in p-type silicon, as predicted by theoretical models. The thermionic current increases by 1.7 times compared to silicon. The distance between the quasi-Fermi level and the Fermi level in n-type silicon is less than this distance in p-type silicon. As a consequence, the number of electrons in the conduction band is smaller. Methods for combating the space charge effect and optimizing the configuration of energy conversion systems are discussed.

Synergy Between PtNPs-Induced Plasmonic Effect and Localized Depletion Layer for Enhancing Performance of Ga₂O₃-Based Heterojunction Solar-Blind Photodetectors

Synergy Between PtNPs-Induced Plasmonic Effect and Localized Depletion Layer for Enhancing Performance of Ga₂O₃-Based Heterojunction Solar-Blind Photodetectors

Achieving High Doping Density in pH-neutral Conjugated Polyelectrolyte Toward Effective Hole-Transporting Materials for Organic Solar Cells.

The lack of effective and non-corrosive hole-transporting layer (HTL) materials has remained a long-standing issue that severely restricts the performance of organic solar cells (OSCs). Most pH-neutral conjugated polyelectrolytes (CPEs) exhibit inferior performance to the acid-doped HTL materials due to their low doping density. In this study, a series of pH-neutral CPEs is designed and synthesized with high doping density as HTL materials. Through an elaborate synthetic route, two sulfonate-terminating alkoxyl side chains can be introduced into thiophene, by which the electron-rich, highly soluble, and chemically stable thiophene monomer is synthesized to enable the subsequent polymerization. The CPE PTT-F exhibit a remarkable self-doping property with an enhanced doping density from 2.01 × 1017 to 7.02 × 1018 cm-3. The high work function and the increased doping density of PTT-F-based HTL decrease the depletion region width from 38.4 to 8.1nm at the anode interface, which minimized the energy loss in hole transport. Consequently, a binary OSC modified by PTT-F-based HTL achieve a high PCE of 18.8%. To the best of the knowledge, this is the highest PCE for OSC employing CPE-based HTL. The results from this work demonstrate an encouraging achievement of realizing exceptional hole collection ability in pH-neutral CPEs.

Novel 4H–SiC MESFET with high ability in gate capacitances control for high frequency applications

The ability to control the gate capacitances is crucial for high-frequency applications, as it affects the device's frequency characteristics, gain and power handling capabilities. We present a 4H–SiC metal-semiconductor field-effect transistor (MESFET) with high gate capacitance control ability for high-frequency applications. The proposed structure (GCC-MESFET) consists of a step gate and a SiC well for adjusting the channel depletion layer and modifying the channel charges. Therefore, the gate capacitances will be controlled (GCC-MESFET). The proposed structure significantly improves the cut-off frequency (fT) and maximum oscillation frequency (fmax). The fT has increased from 23.5 GHz to 33 GHz and the fmax from 50.1 GHz to 54.4 GHz in the proposed structure compared to a conventional structure (C-MESFET). The results show that the DC maximum output power density (Pmax), DC transconductance (gm), cut-off frequency (fT) and maximum oscillation frequency (fmax) of GCC-MESFET improve in comparison with a conventional structure (C-MESFET). It is necessary to mention that the drain current and the breakdown voltage of the proposed structure increase by 48 % and 20 % respectively, compared with the C-MESFET structure due to modifying the channel charges and adjusting the electric field. So, the proposed structure can be used for high current, high voltage, high-power and high frequency applications.

Rational design of chromium-doped NiFe phosphide/phosphate heterostructures for inhibiting chloride ion adsorption and achieving alkaline seawater splitting at industrial-level current density

Electrocatalysts with high activity and corrosion resistance, tailored for industrial-grade current densities, played a crucial role in seawater electrolysis. Here, we synthesized a petal-like Cr-doped NiFe phosphate 'semi-coated' phosphide heterostructure electrocatalyst grown on nickel foam (Cr-NiFeP/PO3@NF). This catalyst demonstrated superior catalytic performance in natural seawater, maintaining stability and only a slight increase in cell voltage after operating continuously for 100 h at a current density of 1 A cm−2. The incorporation of Cr introduced a significant number of unpaired electrons, which enhanced the conductivity of the catalyst, facilitated the creation of electron depletion regions around Ni and Fe, and improved the interaction with adsorption intermediates. Furthermore, the high activity and corrosion resistance during the oxygen evolution reaction (OER) were due to the interaction between the in-situ formed high-valent phosphate and NiFeCrOOH during the anodization process.

The divergent role of straw return in soil O2 dynamics elucidates its confounding effect on soil N2O emission

The divergent effects of straw returns on nitrous oxide (N2O) emissions from soil require elucidation of the underlying mechanisms and factors that explain the inconsistency in in-situ conditions. We conducted a field experiment based on a long-term trial under different regimes of nitrogen (N) fertilization and straw management, complemented by laboratory incubation experiments involving visualized O2 dynamics imaging. In the field trial, we performed hourly basis high-time-resolution measurements of soil matrix oxygen (O2), N2O concentrations and fluxes during N2O “hot moment” events. We found that straw return increased cumulative N2O emissions by 32.7% under conventional high N input (Ncon), but showed no effect on N2O emission under optimized N input (Nopt). In situ O2 content and further microcosm experiments with visualized O2 spatiotemporal distribution suggested that long-term straw return increases porosity and soil O2 content, which reduced N2O emission under low N substrate conditions by improving soil pore structure and aeration during “hot moment” events. By contrast, straw return increased N2O emission via creating short-term O2 depletion zone and triggering denitrification in anoxic microsites when excess N substrate was available. Although straw return showed inconsistent effects on N2O emission under different N application rates, it consistently decreased N2O concentration in the soil matrix during the "hot moment" events, suggesting that straw return increases the transport of the produced N2O in soil matrix to the soil surface. Our study underscores the multifaceted role of straw return in soil O2 dynamics, i.e., stimulating O2 consumption in a short-term microscale of soil, but increasing soil porosity in a long-term mesoscale of soil. This explains the confounding effects of straw management on the production and transportation of soil N2O in situ and emphasizes the importance of optimized N fertilization for reducing the “hot moment” N2O emissions when straw is incorporated.

Performance Comparison of Seed Generation Techniques of Stimulated Brillouin Scattering-Based Microwave Photonics Amplifier and Filter

This work presents a Brillouin amplification performance comparison of seed generation techniques using double-sideband suppressed carrier (DSB-SC) and single-sideband suppressed carrier (SSB-SC) modulations. The SSB-SC is obtained using an optical bandpass filter (OBPF) and in-phase and quadrature Mach-Zehnder modulator (IQ-MZM). All three techniques provide high amplification performance with optical signal-to-noise ratio (OSNR) enhancement of 37.47 dB, 33.14 dB, and 32.67 dB using DSB-SC, SSB-SC/OBPF, and SSB-SC/IQ-MZM, respectively. The best seed generation technique is using the DSB with a signal amplification of 62.47 dB. The technique presents ~4 dB higher OSNR enhancement due to the dual-energy transfer obtained from the beating process of the DSB than SSB. A ~3 dB OSNR reduction is found when pump linewidth (LW) was changed from 1kHz to 50 MHz, which suggests using a low-cost pump source whenever the OSNR reduction is not critical. The work also shows that the three techniques required 10 dBm stimulated Brillouin scattering threshold (SBST) to stimulate the process. An additional analysis of DSB-SC shows that a high-carrier suppression during the seed generation technique using MZMs is insignificant to the amplification performance. The high-carrier suppression produces a high seed signal power that distorts the Brillouin gain spectrum (BGS) and the pump depletion region, hence reducing the Brillouin gain (BG). Since carrier suppression is not a primary consideration, a cost-effective MZM with a modest extinction ratio requirement is allowed. The relaxed requirement of the pump’s linewidth and MZM’s extinction ratio suggest a cost-effective development of the SBS-based optical amplifier with narrow filter bandwidth.

A hBN/Ga2O3 pn junction diode.

The development of next-generation materials such as hBN and Ga2O3 remains a topic of intense focus owing to their suitability for efficient deep ultraviolet (DUV) emission and power electronic applications. In this study, we combine p-type hBN and n-type Ga2O3, forming a pseudo-vertical pn hBN/Ga2O3 heterojunction device. Rectification ratios > 105 (300K) and [Formula: see text]400 (475K) are observed and are amongst the highest values reported to date for ultra-thin hBN-based pn junctions. The measured current under forward bias is ~2mA, which we attribute to the shallow Mg acceptor level (60 meV), and 0.2 µA at -10V. Critically, device performance remains stable and highly repeatable after a multitude of temperature ramps to 475K. Capacitance-voltage measurements indicate widening the depletion region under increasing reverse bias voltage and a built-in voltage of 2.34V is recorded. The hBN p-type characteristic is confirmed by Hall effect, a hole concentration of [Formula: see text] cm-3 and mobility of 24.8 cm2/Vs is achieved. Mg doped hBN resistance reduces by >108 compared to intrinsic material. Future work shall focus on the optical emission properties of this material system.

Separation of planar and edge contributions to total capacitance for accurate doping concentration determination in square silicon photodiodes

Accurately determining the doping concentrations of silicon photodiodes (PDs) is crucial for optimizing their performance in various applications. This study presents a methodology for separating the planar and edge contributions to the total capacitance of square silicon PDs with guard rings. Through capacitance-voltage measurements, we distinguished planar capacitance, which reflects the bulk properties of the silicon PD, from edge capacitance, influenced by device geometry and fringing fields. We demonstrated that the fabricated PDs with guard rings surrounding the active area could be effectively modeled using a coxial-like structure to estimate edge capacitance. Doping concentrations, depletion widths, and resistivities were determined through linear fitting of the inverse square of the measured capacitance per unit area as a function of the reverse bias voltage. All parameters obtained from the full depletion voltage Vd , determined by the intersection of the linear fits for V < Vd and V > Vd , demonstrated agreement within 1σ. Our results underscore the importance of accounting for edge effects to accurately determine doping concentrations from 1/C 2 vs. V plots.