Reverse Current Research Articles

Suppressing the Dark Current Under Forward Bias for Dual‐Mode Organic Photodiodes

AbstractTremendous research efforts are developed to suppress the reverse dark current (Jd) and enhance the responsivity of organic photodiodes (OPDs). The functional layers of traditional OPDs usually follow the principle of energy level alignment to make unobstructed photo‐carriers transport under reverse bias, but this inevitably leads to a large forward Jd. Herein, a universal strategy is proposed to manipulate the carrier dynamics and effectively suppress the forward Jd of OPDs, that is, tuning the energy level and electron traps of the anode interface layers (AILs). The bandgap and electron traps of typical organometallic chelate AIL (PEIE‐Co) can be well controlled by adjusting the component ratio of PEIE and metal ions. The wide bandgap increases the carrier injection barrier under reverse and forward bias, endowing OPD with a much lower Jd; the electron traps induce hole tunneling injection by capturing photo‐generated electrons under forward bias, thereby enabling the photomultiplication effect. The obtained OPD exhibits photoconductive/photomultiplication working mode at reverse/forward bias and the specific detectivity approaches ≈1013/1012 Jones, showing promise for adaptively detecting faint and strong light. This study presents an intelligent strategy to achieve dual‐mode OPDs, paving the way for the multifunctional development of photodetectors.

Interpretation of the degradation and trends in the performance of heterojunction silicon solar cells at low temperature

A compact model that combines numerical simulations using AFORS-HET and accurate equivalent circuit modelling is proposed and used to interpret the origins of the degradation and anomality's in the performance of the a-Si:H/c-Si heterojunction solar cells and its parameters at low temperature. The interpretations are applied to several trends reported on real cells. It is shown that as T decreases the a-Si:H(i) layer is depleted gradually from holes and that the cell operation fails once the layer is totally depleted and becoming intrinsic. The failure is caused by a substantial and sharp increase in the cell series resistance causing the collapse of the fill factor and of the cell current. It is found that at low temperature the open circuit voltage is significantly affected and its temperature dependence strongly distorted by hole depletion in the a-Si:H(i) spacer especially when the TCO work function is not appropriate. It is aslo shown that the S-shape in the cell I-V characteristics under illumination is closely linked to the TCO barrier reverse saturation current which explains its higher probability of appearnce at low temperature. Finally, it is concluded that the HJT cell would perform optimally down to the low 200 K range when the a-Si:H(p) is heavily doped and the front contact is ideally ohmic. Failing to satisfy such conditions the temperature range in which the HJT cell is useful is very limited.

A short-circuit protection scheme for active distribution networks based on improved adaptive current reliability coefficient

Abstract Addressing the issue of misoperation in traditional three-zone current protection caused by the assisted, drawdown, or reverse current due to the large-scale integration of distributed generation (DG) into distribution networks (DNs), an adaptive current short-circuit protection scheme based on local information is proposed for active DNs (ADNs). Firstly, the adaptive current protection reliability coefficients are improved for the setting of protection zones I and II of the lines in the ANDs. On the DG side, an improved reliability coefficient is constructed using an e-exponential function. Subsequently, the distance between the fault point and the busbar is calculated by analyzing the relation between the positive-sequence voltage and positive-sequence current at the measuring point when faults occur at various locations. Based on this distance parameter, the reliability coefficient is adjusted in real time. Finally, the modified adjustable reliability coefficient, along with the online-calculated equivalent impedance and equivalent electromotive force, is used to coordinate the setting of short-circuit protection zones I and II of the lines in the ADNs. Simulation results demonstrate that, compared with traditional adaptive current protection schemes, this proposed scheme is independent of the location of short-circuit fault points, the grid-connected capacity, or the number of DGs, exhibiting better selectivity and reliability.

Fast switching Ga2O3 Schottky barrier power diode with beveled-mesa and BaTiO3 field plate edge termination

Power devices rely on ideal edge termination to suppress the electric field crowding and avoid premature breakdown before the material's critical field is reached. In this work, a hybrid electric field management configuration, featuring the combination of beveled-mesa (BM) termination and high-k oxide BaTiO3 field plate (FP), was implemented in Ga2O3 Schottky barrier diodes (SBDs). This BMFP-SBD realizes a breakdown voltage (BV) of 1.7 kV with extremely low reverse leakage current, outperforming the BM terminated SBD with BV of 0.64 kV and bare SBD with BV of 0.22 kV. Based on the temperature-dependent reverse characteristics, the dominant leakage mechanism transforms from Poole–Frenkel (P–F) emission in BM-SBD to variable-range-hopping (VRH) in BMFP-SBD at high bias. In particular, under switching conditions of di/dt up to 420 A/μs, the BMFP-SBD exhibits superior dynamic switching characteristics with a short reverse recovery time of 10.1 ns, which are comparable with those in advanced commercial SiC SBDs. These findings underscore the potential of Ga2O3 SBD enabled by BM and high-k FP edge termination for high-speed and high-voltage power electronics applications.

A highly efficient adaptive body bias CMOS rectifier with double-side feedback at a tone of 2.4 GHz

ABSTRACT In this paper, a highly efficient adaptive body bias CMOS rectifier employed with double side feedback, operating with 2.4 GHz frequency, is proposed for radio frequency energy harvesting. The proposed circuit is built with 45 nm TSMC CMOS technology. In the suggested architecture, the double side feedback along with body bias is used to regulate threshold voltage. The use of PMOS transistors as a diode in reverse bias configuration has restricted the reverse current without compromising the forward current. This design has gained a maximum PCE of 82.25% and 77.29% at an input power of −23.90dBm and −23.74dBm and 500K and 100K load, respectively. The circuit has maintained a wide dynamic range of 30dbm at PCE >30% and registered an input sensitivity of −10.07dBm for attaining a DC output voltage of 1 V as compared to the previous works.

Enhancing optical output power efficiency in nitride‐based green micro light‐emitting diodes by sidewall ion implantation

AbstractThough micro‐LED (light‐emitting diode) displays are considered the emerging display technology, the micron‐scale LED chip size encounters severe efficiency degradation that may impact the power budget of the displays. This work proposes an ion implantation method to deliberately create a high‐resistivity sidewall in the InGaN/GaN green LED. Our study demonstrates that ion implantation suppresses reverse leakage current due to the mitigation of sidewall defects. For an LED mesa size of 10 × 10 μm2, optical output power density is improved by 36.2% compared to the device without implantation. Compared to a larger 100 × 100 μm2 device without implantation, we achieve only 21.3% degradation of output power density under 10 A/cm2 injection for a 10 × 10 μm2 LED with implantation. In addition, the ion implantation method can lower the wavelength shift by reducing light emission from the region near the sidewall (where the amount of Indium [In] clustering differs from the mesa region). The results show promise in addressing the efficiency challenges of micro‐LED displays by selective ion implantation.

Asymmetric trench SiC MOSFET with integrated channel accumulation diode for enhanced reverse conduction and switching characteristics

A novel asymmetric trench Silicon Carbide Metal Oxide Semiconductor Field Effect Transistor (SiC MOSFET), featuring an integrated channel accumulation diode (CAD-MOS), has been proposed and investigated through numerical simulation. This innovative design aims to mitigate switching losses and eliminate the bipolar degradation of the body diode. The current spreading layer (CSL) channel, strategically positioned in the centre of the dummy gate, offers a low-barrier reverse conduction path. This represents a substantial advancement over the traditional PN body diode, significantly reducing the reverse conduction voltage drop from 2.84 V in the PN body diode to a mere 1.39 V in the CAD-MOS. Meanwhile, the reverse recovery charge of the CAD-MOS is reduced to 0.95 μC/cm2, and the peak reverse recovery current stands at 45 A/cm2. Compared to conventional asymmetrical trench SiC MOSFET (CON-MOS), the CAD-MOS exhibits a 68.1 % reduction in reverse recovery charge and a 63.4 % decrease in peak reverse recovery current. The split-gate design also reduces the device gate to source capacitance (CGS), resulting in a 17.4 % reduction in total switching losses to 3.64 mJ/cm2. CAD-MOS also exhibits a reduced gate turn-on charge and demonstrates an enhancement in high-frequency figure of merit (HF-FOM) by 8.1 %.

Optimizing Forward Drop and Reverse Leakage Trade‐Off in AlGaN/GaN Lateral Diode with Schottky‐Metal‐Insulator‐Semiconductor Cascode Anode

Herein, AlGaN/GaN lateral diode with the Schottky‐Metal‐Insulator‐Semiconductor (MIS) cascode anode (CALD) to optimize forward voltage drop (VF) and reverse leakage current (ILEAK) trade‐off is proposed. In the CALD device, a normally‐on Ni/HfO2/AlGaN MIS‐controlled channel as well as a lateral Ni/GaN Schottky contact are cascoded at the anode. The designed normally‐on MIS‐controlled channel has high electron concentration at forward bias and prevents high electric‐field at reverse bias, which ensure both low VF and low ILEAK. Meanwhile, the Ni/GaN Schottky contact with a high Schottky barrier height further suppresses the ILEAK. As a result, the fabricated CALD demonstrates an optimized VF–ILEAK trade‐off relationship, including a low VF of 1.6 V and a low ILEAK of 5.2 × 10−8 A mm−1 (at reverse voltage of 400 V), together with a high breakdown voltage (BV) >700 V. These high performances suggest that the CALD can be a promising candidate for GaN power diode applications requiring a better VF–ILEAK trade‐off.

Schottky barrier memory based on heterojunction bandgap engineering for high-density and low-power retention

Dynamic random-access memory (DRAM) has been scaled down to meet high-density, high-speed, and low-power memory requirements. However, conventional DRAM has limitations in achieving memory reliability, especially sufficient capacitance to distinguish memory states. While there have been attempts to enhance capacitor technology, these solutions increase manufacturing cost and complexity. Additionally, Silicon-based capacitorless memories have been reported, but they still suffer from serious difficulties regarding reliability and power consumption. Here, we propose a novel Schottky barrier memory (SBRAM), which is free of the complex capacitor structure and features a heterojunction based on bandgap engineering. SBRAM can be configured as vertical cross-point arrays, which enables high-density integration with a 4F2 footprint. In particular, the Schottky junction significantly reduces the reverse leakage current, preventing sneak current paths that cause leakage currents and readout errors during array operation. Moreover, the heterojunction physically divides the storage region into two regions, resulting in three distinct resistive states and inducing a gradual current slope to ensure sufficient holding margin. These states are determined by the holding voltage (Vhold) applied to the programmed device. When the Vhold is 1.1 V, the programmed state can be maintained with an exceptionally low current of 35.7 fA without a refresh operation.

Rational Doping Strategy to Build the First Solution‐Processed p‐n Homojunction Architecture toward Silicon Quantum Dot Photodetectors

Semiconductor p‐n homojunction is a requisite building block of operating transistors and diodes which make up the modern electronic circuits and optoelectronic applications. However, it has been so far limited to bulk form of single crystals such as silicon (Si) or gallium arsenide. Herein, a brand‐new method of constructing p‐n homojunction architectures that breaks through the limitation is presented. Colloidal inks of p‐type and n‐type Si quantum dots (QDs) are synthesized by thermal disproportionation of (HSiO1.5)n doped with boron or phosphorus, followed by surface ligand engineering. Analysis combining UV photoelectron spectroscopy, electron spin resonance, and current–voltage characteristics confirms that an orthogonal solvent trick makes clean interfaces between n‐type and p‐type SiQD layers without disruption on film formation. The forward and reverse current–voltage characteristics of the diode, along with various spectroscopic characterizations, demonstrate the formation of the first p‐n homojunction of SiQDs. The self‐powered photodiode provides a tunable response specific to the wavelength.

Photodetector performance analysis of a hybrid MnPc/DLC device with high photoresponsivity, sensitivity, and On/Off ratio

The fabrication and characterization of high-performance devices for optoelectronic applications, particularly their response to incident light, are crucial. In this study, a MnPc/DLC device was fabricated using thermal evaporation and magnetron sputtering techniques, and its fundamental optoelectronic properties were characterised. Key diode parameters including barrier height, ideality factor, reverse saturation current, series resistance, and shunt resistance were determined using several methods, such as TE, Ohm's Law, the modified Norde method, and the Mikhelashvili method. The results from these methods were found to be consistent with varying light intensities. Additionally, photodetector parameters of the MnPc/DLC device were measured at ±1 V under light intensities of 20, 40, 60, 80, and 100 mW/cm2, and the findings were compared with the literature. The maximum values for photocurrent, photoresponsivity, photosensitivity, specific detectivity, and on/off ratio were 6.41 × 10−2 A, 2.49 A/W, 2.02 × 105, 5.8 × 109 Jones and 2.06 × 103, respectively. Notably, the photocurrent, photoresponsivity, photosensitivity, and on/off ratio values were found to be significantly higher and more promising compared to those reported in the literature.

MOS-structured MoS2/GaN Schottky barrier diodes with high on/off current ratio and low threshold voltage

GaN Schottky barrier diodes (SBDs) have been investigated for a variety of power applications. However, the problems of low on/off current ratio and high threshold voltage caused by the difficult high-quality doping restrict its utilization in power devices. In this work, quasi-vertical MoS2/GaN SBDs with Metal-Oxide-Semiconductor (MOS) structure have been proposed. The MOS structure is formed by the part of anode (Ni/Au) over the Al2O3, Al2O3, and monolayer MoS2. Monolayer MoS2 exhibits n-type doping and p-type doping under forward bias and reverse bias, respectively, which realizes an adjustment in the Fermi level of the monolayer MoS2, resulting in a change in the resistance of the SBDs. The as-prepared SBDs present a high on/off current ratio of 2.40 × 1011, a low threshold voltage of 0.55 V at 1 A/cm2, and a low reverse leakage current of 2.50 × 10−10 A/cm2 at −1 V. This work shows that the MOS-structured MoS2/GaN SBDs are promising for next-generation power electronics.

Comparative Analysis of 50 MeV Li3+ and 100 MeV O7+ Ion Beam Induced Electrical Modifications in Silicon Photodetectors

This article investigates the impact of 100 MeV O7+ and 50 MeV Li3+ ions on Silicon Photodetectors, focusing on their electrical characteristics with similar Sn/Se ratios. Elevated ion fluences led to a significant rise in the ideality factor “n”, indicating the presence of Generation-Recombination (G-R) current due to introduced defects, especially those with deep energy levels in the forbidden gap acting as G-R centers. While Ideality factor (n) values decreased for oxygen ions at maximum fluence, they increased for lithium ions, reflecting consistent patterns in series resistance (Rs) and reverse leakage current (IR), attributed to ion-induced defects. Oxygen ions showed a monotonic variation in Rs, whereas lithium ions exhibited a slight reduction at maximum fluence, possibly due to defect annihilation. Despite differing Se values, 50 MeV Li3+ ions demonstrated improved device characteristics, suggesting potential defect annihilation. The ratio of Sn to Se indicated comparable damage contributions from nuclear and electronic energy. Additionally, TRIM computations revealed non-uniform damage distributions, with ions penetrating deep into the substrate, away from the n+/p junction.

Leakage current in GaN-on-GaN vertical GaN SBDs grown by HVPE on native GaN substrates

This study investigates leakage mechanisms in vertical GaN-on-GaN Schottky barrier diodes (SBDs) and demonstrates effective mitigation strategies. The fabricated devices exhibit low reverse leakage current (1 × 10−5 A/cm2 at −200 V) and a high Ion/Ioff ratio (∼1010), surpassing the performance of GaN SBDs on foreign substrates. We elucidate dominant leakage mechanisms—thermionic emission, Poole–Frenkel emission, and variable-range hopping—and their evolution with temperature and bias. Optimized fabrication processes, including defect etching and a novel dual-layer passivation technique, achieve over a 1000-fold reduction in leakage current.

GaN Nano Air Channel Diodes: Enabling High Rectification Ratio and Neutron Robust Radiation Operation.

Nano air channel transistors (NACTs) provide numerous advantages over traditional silicon devices, including faster switching speeds, higher operating frequencies, and enhanced radiation hardness attributable to the ballistic transport of electrons. In the development of field-emission-based integrated circuits, low-power consumption rectifying nano air channel diodes (NACDs) play a crucial role. However, achieving rectification characteristics in NACDs is challenging due to their structural and material symmetry. This paper proposes a vertical GaN NACD with a consistent nano air channel fabricated using IC-compatible processes. The GaN NACD exhibits an exceptionally low turn-on voltage of 0.3 V while delivering a high output current of 5.02 mA at 3 V. Notably, it demonstrates a high rectification ratio of up to 2.2 × 105, attributing to significant work function disparities within the GaN-Au structure, coupled with the reduction of Au surface roughness to minimize reverse current. Furthermore, the junction-free structure and superior material properties of GaN enable the NACD to be suitable for use in radiation-rich environments. With its potential as a fundamental component of ultrafast and ultrahigh-frequency integrated circuits, this intriguing and cost-effective rectifying diode is anticipated to garner widespread interest within the electronics community.

A Study on the Impact of Different PV Model Parameters and Various DC Faults on the Characteristics and Performance of the Photovoltaic Arrays

PV systems play a vital role in the global renewable energy sector, and they require accurate modeling and reliable performance to maximize the output power. This research presents a thorough analysis and discussions on the effects of different PV models’ parameters and certain specific faults on the performance and behavior of the photovoltaic systems under different temperature and irradiation conditions. It provides a detailed analysis of how several parameters affect the performance of the PV arrays, for instance, the series resistance, shunt resistance, photocurrent, reverse saturation current, and the diode ideality factor. These parameters were extracted mathematically and verified with the help of wide-ranging simulations and practical experiments. Additionally, the investigation of the effect of DC faults, including line-to-line, line-to-ground, partial shading, and complete shading faults on PV arrays, provides important fundamentals for fault detection and classification, thus improving the efficiency and protection of PV systems. It can, therefore, be stated that the outcomes of this research will assist in the enhancement of PV systems in terms of design, operation, and maintainability of photovoltaic plants, as well as contribute positively to the advancement of sustainable solar energy technology.

The effect of Cu-doping to the DLC interlayer on the temperature dependent current-conduction mechanisms and barrier shape of the Schottky devices

The objective of this study is to determine the temperature and voltage-dependent current conduction mechanisms (CCMs) of the Al/Cu-doped DLC/p-Si Schottky device. It is aimed to obtain extensive and detailed data by current-voltage (I–V) measurements taken with 0.3 V voltage steps in the ±4 V voltage range, at 30 K intervals from 80 K to 410 K. Firstly, an examination of the semi-logarithmic I–V curve revealed that the low temperature (LTs, 80 K–170 K), medium temperature (MTs, 200 K–290 K) and high temperature (HTs, 320 K–410 K) regions should be examined separately. The basic parameters of the Schottky device such as the ideality factor (n), reverse saturation current (Io) and zero-biasing potential barrier height (ΦBo) were obtained separately for LTs, MTs and HTs by the Thermionic Emission (TE) theory. The results obtained show that the device deviates from ideality, especially in LTs and HTs, and the n values decrease with increasing temperature, while the ΦBo values increase. The analysis of the presence of other CTMs in the Schottky device revealed that Field Emission (FE) and Thermionic Field Emission (TFE) were effective in LTs and MTs, while FE was effective in HTs. Since it is thought that quantum mechanical CTMs cannot be the cause of such a deviation from ideality due to the interface layer thickness, the existence of Gaussian Distribution originating from lateral barrier inhomogeneity was investigated. As a result, it is concluded that the Multiple Gaussian Distribution (MGD) is dominant in the possible CTMs of the Schottky device.

Effects of athermal carrier injection on Co-60 gamma-ray damage in SiC merged-PiN Schottky diodes

Co-60 gamma irradiation of SiC merged-PiN Schottky (MPS) diodes up to fluences of 1 Mrad (Si) produces increases in both forward and reverse current, with less damage when the devices are biased during irradiation. Subsequent injection of minority carriers by forward biasing at 300 K can partially produce some damage recovery, but at high forward biases also can lead to further degradation of the devices, even in the absence of radiation damage. Recombination-enhanced annealing by carrier injection overall is not an effective technique for recovering gamma-induced damage in SiC MPS diodes, especially when compared to other near athermal methods like electron wind force annealing.

A Guide to Electrocatalyst Stability Using Lab-Scale Alkaline Water Electrolyzers

Green hydrogen from low-temperature water electrolysis has received significant attention with a projected thousand-fold global capacity expansion by 2030.1 Electrocatalyst research is crucial for water electrolysis technologies and has garnered substantial attention. However, despite a surge in publications centered on promising electrocatalytic materials, often claiming "outstanding" performance, few studies have scaled these materials to more realistic setups. This gap primarily stems from the inadequacy of testing environments and operating conditions in academic research. The prevalent use of three-electrode cell configurations fails to mimic practical electrolyzer conditions accurately.2,3 Electrocatalytic performance in these setups does not effectively represent real electrolysis devices operating in zero-gap configurations. Therefore, implementing stability tests in realistic device configurations is essential to assess compounded instability from all components, including the catalyst.2,4 Our group has developed and optimized a lab-scale electrochemical flow cell for alkaline water electrolysis (AWE), refined over four years of dedicated research (Figure 1a).4–7 This work outlines the operation of this device in a laboratory environment, focusing on accelerating the evaluation of electrocatalytic materials and their durability in alkaline conditions. We examined the performance of this lab-scale electrolyzer under industrially relevant conditions, including varying temperatures (Figure 1b). We examined the stability of three standard electrocatalytic materials to demonstrate the electrolyzer performance under fluctuating current conditions, including a benchmark NiFe anode for the oxygen evolution reaction (Figure 1c) and nickel nitride (Ni3N) precatalyst (Figure 1d). Furthermore, we propose a standardized protocol for assessing electrocatalysts under fluctuating and reverse currents, contributing to the understanding of catalyst deactivation. This initiative marks a significant advancement in AWE electrocatalysis research. Our goal is to establish an effective and straightforward protocol for evaluating and validating electrocatalysts in AWE, fostering accurate performance comparisons.

Dynamic Activity and Stability of Transition Metal (oxy)Hydroxide Oxygen Evolution Electrocatalysts Under Steady and Intermittent Operation

The oxygen evolution reaction (OER) plays a critical role in several energy conversion technologies, requiring catalysts that combine high activity with stability for successful commercialization. Catalysts from first-row transition metal oxides have garnered considerable attention in this context. Their noteworthy OER activity and stability in alkaline environments position them as a more economical option than their counterparts in acidic media. However, recent studies have shown that these materials tend to experience significant dissolution issues and undergo changes in their chemical composition, a phenomenon observed even during steady-state operation.1–3 Addressing these challenges is essential for advancing commercial energy conversion technologies, which often face intermittent loads and reverse currents. A deeper understanding of the dynamic reconstruction under fluctuating conditions is crucial for developing more durable and efficient electrocatalytic materials.4 In this work, we investigate the dynamic performance of nickel cobalt (oxy)hydroxide electrocatalytic films containing iron active sites in alkaline media under steady and intermittent operation. First, we systematically examine the changes in OER catalytic activity in a typical three-electrode configuration, focusing on the incorporation and redissolution of iron and cerium during different electrochemical conditioning methods. As shown in Figure 1a, conditioning using chronopotentiometry decreases the OER overpotential without significantly shifting the redox peak. In contrast, conditioning using cyclic voltammetry significantly shifts the redox peak position (Figure 1b). These differences are attributed to the (oxy)hydroxide film thickness, which forms in situ during conditioning and affects the Fe dissolution and incorporation rates based on the conditioning method.5 We use different analytical techniques to probe chemical transformations during conditioning. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) are utilized to analyze compositional changes in the electrocatalytic films. Moreover, inductively coupled plasma mass spectrometry (ICP-MS) tracks metal dissolution.Next, we utilize an electrochemical flow electrolyzer with a zero-gap configuration, integrated with online ICP-MS and post-experimental TOF-SIMS and XPS, to study the reconstruction of these electrocatalysts under intermittent conditions. A NiFe anode operating in 6 M KOH with 1 ppm of Fe3+ shows a 40-mV change after 120 cycles of alternating low and high currents, including a simulated shutdown step (Figure 1c). This cell potential change, becoming more negative with continued cycling (Figure 1d), is attributed to the shutdown step. Our findings underscore how operating conditions affect the dynamic reconstruction of electrocatalytic materials, offering critical insights for developing more robust and resilient materials suitable for commercial applications.