Charge Storage Effect Research Articles

Multifunction realization in MoS2/WS2/h-BN heterojunction: Integrated self-powered high-performance photodetection, visualization, nonvolatile memory, and synaptic simulation

Nowadays, efficient performance, functional diversification, device miniaturization and systematic integration are the trends for developing new electronic information technology. However, photodetectors with only optoelectronic detection functions cannot satisfy the growing demands of the multifunction required in single devices. This paper presents a MoS2/WS2/h-BN van der Waals heterojunction device realizing multifunctional applications which integrated self-powered high-performance photodetection, visualization, nonvolatile memory, and synaptic simulation. The heterojunction achieves a high responsivity of 9.28 A/W, an excellent specific detectivity of 6.1×1012 Jones, a large external quantum efficiency of 2358 %, a considerable on/off ratio of 7×105 and an ultrafast response time of 0.6 μs at 1 V bias under 488 nm laser irradiation. Besides, the photodetector shows excellent photovoltaic characteristics with a short-circuit current of 0.22 μA and an open-circuit voltage of 0.34 V. Moreover, the device also shows a favorable optical response to 532 and 633 nm lasers. The device also realizes visualization and can be used as an imaging sensor. In addition, the device integrates nonvolatile memory function due to the charge storage effect of h-BN and h-BN/SiO2 interface. Furthermore, biological synaptic functions, such as the memory process, short- and long-term plasticity, and double pulse facilitation, are also successfully simulated. This work realizes the high-performance and multifunctional applications of MoS2/WS2/h-BN device based on a new strategy of utilizing h-BN as a heterojunction substrate.

Boosting electrochemical energy storage properties of SrGd2O4 through Yb3+ and Tm3+ rare earth ion doping

Electrochemical supercapacitors represent advanced energy storage devices that excel in the swift storage and delivery of electrical energy, effectively bridging the gap between conventional capacitors and batteries. The present work, aimed to investigate charge storage properties of SrGd2O4 and rare earth ions Yb3+ and Tm3+ doped in SrGd2O4. Both materials were prepared via simple sol-gel synthesis and characterized by XRD, XPS, and FE-SEM with EDS. Characterization confirmed the presence of Tm3+ and Yb3+ in the SrGd2O4 matrix with a uniform distribution of elements. The charge storage behavior of pure SrGd2O4 and SrGd2O4:Yb4Tm1 in various electrolytes was thoroughly explored. Large electrochemical potential windows were shown by both electrode materials in aqueous 6 M KOH (1.7 V), which is essential for supercapacitors to achieve high specific energy. Furthermore, SrGd2O4:Yb4Tm1 demonstrated a substantially more pronounced charge storage effect in 6 M KOH electrolyte, with almost double times higher specific capacitance values compared with an un-doped SrGd2O4 sample. The main impact on the electrochemical window had matrix SrGd2O4, while the main impact on specific capacitance had rear earth dopants (Yb3+ and Tm3+). Improved charge storage characteristics of SrGd2O4:Yb4Tm1 were also evident through a notable reduction in overall resistance observed in electrochemical impedance spectroscopy experiments. Concerning the two-electrode GCD measurements, the SrGd2O4:Yb4Tm1 electrode in 6 M KOH showed a specific capacitance of 143 F g−1, with the specific energy of 12.5 Wh kg−1 at 0.6 A g−1. These findings demonstrate the potential of rare earth ion doping in enhancing the energy storage properties of SrGd2O4, offering promising avenues for the development of high-performance supercapacitors.

Efficient photocatalytic hydrogen evolution of g-C3N4/Vs-SnS2/CdS through a sulfur vacancy-rich SnS2 induced charge storage effect

Photocatalytic hydrogen production using semiconductors is one of the most promising routes for sustainable energy production.

Spatial charge storage on the nitrogen-doped graphene for ultrafast supercapacitors with high EDLC capacity

The limited specific surface area of carbon substance restricts the raise of the electrochemistry double layer capacitance (EDLC). If the charge storage location could be extended from surface to space, the EDLC of carbon materials can be greatly improved. Here, an original spatial charge storage mechanism according to the counterion effect from Fe (CN)6 3− ions bridged by nitrogenous groups is proposed, which can provide additionally spatial charge storage for EDLCs. More importantly, the graphene designed based on this structure can achieve a high storage capacity of 334 F g−1 at 0.5 A g−1 (the rate retention is 64% at 50 A g−1) in 6 M KOH electrolyte, much higher than the sample without space charge storage effect (from 270 to 160 F g−1). This novel strategy for the design of graphene with multiple spatial active sites can be extended to other carbon materials, which can propose a new idea for the development of carbon materials in the field of energy storage.

A 4H-SiC semi-super-junction shielded trench MOSFET: p-pillar is grounded to optimize the electric field characteristics

A 4H-SiC trench gate metal–oxide–semiconductor field-effect transistor (UMOSFET) with semi-super-junction shielded structure (SS-UMOS) is proposed and compared with conventional trench MOSFET (CT-UMOS) in this work. The advantage of the proposed structure is given by comprehensive study of the mechanism of the local semi-super-junction structure at the bottom of the trench MOSFET. In particular, the influence of the bias condition of the p-pillar at the bottom of the trench on the static and dynamic performances of the device is compared and revealed. The on-resistance of SS-UMOS with grounded (G) and ungrounded (NG) p-pillar is reduced by 52% (G) and 71% (NG) compared to CT-UMOS, respectively. Additionally, gate oxide in the GSS-UMOS is fully protected by the p-shield layer as well as semi-super-junction structure under the trench and p-base regions. Thus, a reduced electric-field of 2 MV/cm can be achieved at the corner of the p-shield layer. However, the quasi-intrinsic protective layer cannot be formed in NGSS-UMOS due to the charge storage effect in the floating p-pillar, resulting in a large electric field of 2.7 MV/cm at the gate oxide layer. Moreover, the total switching loss of GSS-UMOS is 1.95 mJ/cm2 and is reduced by 18% compared with CT-UMOS. On the contrary, the NGSS-UMOS has the slowest overall switching speed due to the weakened shielding effect of the p-pillar and the largest gate-to-drain capacitance among the three. The proposed GSS-UMOS plays an important role in high-voltage and high-frequency applications, and will provide a valuable idea for device design and circuit applications.

2D Materials Integrated CNT Hybrid Paper Electrodes for Flexible All-Solid-State Supercapacitors

Flexible supercapacitors (SCs) have attracted growing interests as the power source for portable and wearable electronics. Carbon nanotubes (CNTs) are emerged as one of the promising materials for flexible SC electrodes due to their excellent high electrical conductivity, high mechanical strength, large surface area, and functionalization ability. CNTs can be assembled into several macroscopic forms based on the applications. In the present work, the CNT buckypapers integrated with 2D materials such as graphene and transition metal sulfides (TMDs) especially, tin sulfide (SnS2) nanoparticles were prepared using a simple mould casting method. The flexible and free-standing, interface-enhanced CNT paper having homogeneously dispersed 2D materials was prepared. The hybridized CNT papers were thoroughly characterized to elucidate their structural and surface properties. Finally, such hybrid CNT papers were used as binder-free, free-standing electrodes for the fabrication of flexible-all-solid-state supercapacitors. The electrochemical performance (CV, GCD, EIS) of the as obtained the symmetric and asymmetric devices were assessed to evaluate the charge storage performance and effect of 2D materials on the charge storage capability and stability were studied. Figure 1

Electric Energy Storage Effect in Hydrated ZrO2-Nanostructured System.

The dimensional effect of electric charge storage with a density of up to 270 μF/g by the hydrated ZrO2-nanoparticles system was determined. It was found that the place of localization of different charge carriers is the generalized heterophase boundary-nanoparticles surface. The supposed mechanism of the effect was investigated using the theory of dispersed systems, the band theory, and the theory of contact phenomena in semiconductors, which consists of the formation of localized electronic states in the nanoparticle material due to donor–acceptor interaction with the adsorption ionic atmosphere. The effect is relevant for modern nanoelectronics, microsystem technology, and printed electronics because it allows overcoming the basic physical restrictions on the size, temperature, and operation frequency of the device, caused by leakage currents.

Electrical charge storage effect in carbon based polymer composite for long-term performance enhancement of the triboelectric nanogenerator

The triboelectric nanogenerator (TENG) is considered as a promising small-scale energy harvester with its advantages such as material selection diversity, design flexibility, and versatile application. Although there are numerous reports about mechanism to instantaneously enhance the output performance of the TENG, there have been few reports about the long-term output enhancement of the TENG with dynamic movement of charges in the TENG. In this study, PDMS based carbon black composite (PCC), which has excellent charge storage ability, is utilized as a contact layer of the TENG and the effect of the charge storage ability on the long-term transient output performance of the TENG is investigated. As the carbon content in composite varies, the long-term output performances of the TENGs exhibit significantly different behavior with the different charge storage ability of the contact layer. Use of PCC with derived optimal carbon black content exhibit more than 2 times increase of long-term output performance of the TENG. To effectively operate the TENG adopting PCC with high number of contact/separation cycles, a rationally designed power transmission unit based on scotch yoke mechanism is applied and as a result, a ubiquitous rotational motion around us could be easily harvested. The system generates the output current of 320 μA and it easily turns on hundreds of light emitting diodes as well as the commercial electronic devices. The present strategy would provide the outstanding approach to enhance the long-term output performance of the TENG.

NanoZnO Modified Polymer Electret Electrodes for Cyclic Voltammetry of Some Synthasized Anils

Preparation and characterization of pure and nano-ZnO doped PVDF-PMMA polymer blend-nanocomposites for investigating the charge storage and transfer effects have been studied. Fourier transform infrared (FTIR) was used for characterization and structure elucidation of the blended polymers. Polymer microstructure, chain conformation and polymer morphology were studied to establish the structure activity relations. Cyclic voltammetry (CV) was chosen to study the electronic properties of the modified polymers as it furnishes information as a function of an energy scan. The effectiveness of CV results from its capability of rapidly observing the redox behavior of the analyte over a wide potential range. Electrode reactions of the intermediates and the products formed during the forward scan have been studied for sulphonamide analogues of synthesized azomethines. Comparative electro activity of plain glassy carbon electrode and the PVDF-PMMA polymer blend-nanocomposite electrets modified electrode was studied.

Investigation of Electrical Contacts to p-Grid in SiC Power Devices Based on Charge Storage Effect and Dynamic Degradation

P-grid is a typical feature in power devices to block high off-state voltage. In power devices, the p-grid is routinely coupled to an external electrode with an Ohmic contact, but Schottky contact to the p-grid is also proposed/adopted for certain purposes. This work investigates the role of contact to p-grid in power devices based on the commonly adopted technology computer-aided design (TCAD) device simulations, with the silicon carbide (SiC) junction barrier Schottky (JBS) diode as a case study. The static characteristics of the JBS diode is independent of the nature of the contact to p-grid, including the forward voltage drop (VF) and the breakdown voltage (BV). However, during the switching process, a Schottky contact would cause storage of negative charges in the p-grid, which leads to an increased VF during switching operation. On the contrary, an Ohmic contact provides an effective discharging path for the stored negative charges in the p-grid, which eliminates the dynamic degradation issues. Therefore, the necessity of an Ohmic contact to p-grid in power devices is clarified.

Enhancing output performances and output retention rates of triboelectric nanogenerators via a design of composite inner-layers with coupling effect and self-assembled outer-layers with superhydrophobicity

Abstract Low output performances and output retention rates in high humid environments represent serious challenges that have interrupted the large-scale application of triboelectric nanogenerators (TENGs) as portable power supplies and self-powered sensors. Existing approaches of tribo-material optimization and device structure design remain limited in solving the problems of low electrical outputs and output retention rates for TENGs. Here, achieving high electrical outputs and output retention rate in a TENG based on a multi-effect inner-layer and a superhydrophobic outer-layer is first proposed by an organic-inorganic composite and simple self-assembly electrospinning. The inner-layer consisting of polyimide (PI) and 0.85Na0.5Bi0.5TiO3-0.15SrTiO3 (NBT-15ST) ceramic particles (CPs) can distinctly enhance the electrical performances of the device by coupling charge storage effect and hysteretic dielectric polarization. Under a maximum instantaneous force of 50 N, the device delivers a voltage of 1020 V and a current density of 32.5 μA cm−2. Meanwhile, the superhydrophobic outer-layer with novel biomimetic multilevel structures endowing the device with a superior output retention rate of 50% at a high relative humidity of 80%. This work provides a new strategy to optimize the electrical outputs of the TENG and extends its application in humid conditions.

Defect studies on short-wave infrared photovoltaic devices based on HgTe nanocrystals/TiO2 heterojunction

Narrow bandgap (<0.5 eV) colloidal semiconductor nanocrystals (e.g. mercury chalcogenides) provide practical platforms for next generation short wave infrared, mid wave infrared and long wave infrared optoelectronic devices. Until now, most of the efforts in the field of infrared active nanocrystals have been taken on synthesizing nanocrystals, determining quantum states and building different geometries for optoelectronic devices. However, studies on interface trap states in the devices made from these narrow band gap nanocrystals are mostly unexplored. Herein, we investigate the defects or traps in these nanocrystals—embedded devices, which will be critical for improving their optoelectronic performance. In this article, we fabricate HgTe nanocrystals/TiO2 based photovoltaic devices and used capacitance-voltage (C–V) and deep level transient spectroscopy (DLTS) to investigate and obtain quantitative information on deep level trap states. Interestingly, frequency dependent C–V measurements show two peaks in the capacitance at lower frequency (<40 kHz), which is attributed to the presence of trap states. However, at high frequency the presence of a weak hump-like structure almost at the center of above two peaks validate the role of interface traps. DLTS studies show that traps at the interface of HgTe nanocrystals/TiO2 acts as recombination centers having activation energies of 0.27, 0.4 and 0.45 eV with corresponding trap densities of 1.4 , 1. and 1. and estimated capture cross-sections of 6.3 , 7.5 and 3.7 , respectively. In this work, DLTS has revealed the existence of interface trap states and the frequency dependent capacitance measurements corroborate the effect of charge storage on the heterostructures built from these nanocrystals that helps in the development of futuristic devices.

Charge storage impact on input capacitance in p-GaN gate AlGaN/GaN power high-electron-mobility transistors

In this paper, input capacitance (CISS) of p-GaN gate AlGaN/GaN power high-electron-mobility transistors (HEMTs) is systemically investigated. CISS includes gate-to-source capacitance (CGS) and gate-to-drain capacitance (CGD). In comparison with the normally-on HEMTs, it is found that the phenomenon of CISS variation is different in the commercial p-GaN gate HEMTs. The unique charge storage effect in the typical p-GaN layer is adopted and discussed to explain the variation of CISS and establish the underlying mechanism. Owing to the depletion of holes, net negative charges are induced in the p-GaN layer under an off-state drain bias. It is demonstrated that the negative charge storage makes significant contribution to the increase of CGS before the two-dimensional-electron-gas channel under source-field-plate (SFP) pinches off. Due to the clamped electric field distributions at drain-side edge of the p-GaN layer, the charge storage stops changing CGS after the SFP pinche-off. Additionally, the storage has a minor influence on the variation of CGD. Verified by the experimentally calibrated TCAD simulation, this work reveals a novel mechanism of charge storage impact on CISS variation in p-GaN gate AlGaN/GaN power HEMTs, which is of benefit to the CISS related capacitance design and gate driver optimization of the devices.

Flyback CC/CV AC–DC converter with high precision and reliability based on two-winding topology

Due to the rapid development of consumer electronics, the demand for power adapters is increasing. Therefore, a high-precision, high-reliability, low-cost flyback AC–DC converter without auxiliary winding was proposed in this paper. The converter adopted a primary-side regulation (PSR) topology to sample the output voltage and current from the primary inductor, and adjusted the switching frequency to achieve a constant output voltage. By alternately switching the main power BJT and the auxiliary MOSFET, with the advantage of the base charge storage effect, the chip was powered by the primary-side current. A primary-side sampling resistor was placed at the negative terminal of the ground potential of the chip, which approached real-time monitoring of the primary-side current. This improved the reliability and output accuracy of the system. To verify the feasibility and performance of the proposed circuit, an IC controller was designed and fabricated under the NEC 1 μm BCD process. Experimental result showed that deviations of the output voltage and current do not exceed ± 1.4% and ± 2.3%, respectively. These results also showed that the maximum conversion efficiency can reach a level of 78.7%, which satisfies the consumer market very well.

Design of a High Accuracy PSR CC/CV AC–DC Converter Without Auxiliary Winding

A high accuracy ac–dc converter without auxiliary winding has been proposed in this article. The converter adopts primary-side regulation (PSR) topology, sampling output voltage and current from primary inductance, then adjusting switching frequency and primary peak current of the power converter to regulate output. By switching the main power transistor and the auxiliary switching transistor alternately on and off , and using base charge storage effect to generate driving voltage, the converter charges chip-powering capacitor by primary-side current, instead of auxiliary winding. Compared to the traditional three-winding topology, the proposed converter not only achieves higher performance, but also eliminates one winding, which means fewer external components are used, transformer becomes simpler, and system cost is lower. The control chip was implemented in NEC 1- μ m HVCMOS process, and a 5 V/1 A prototype has been built to verify its feasibility. Experimental results show that the control chip can be powered perfectly, and the deviations of output voltage and current are within ±1.3% and ±2.5% under different input and load conditions, whereas maximum conversion efficiency can reach a level of 78.9%.

Modeling of IGBT With High Bipolar Gain for Mitigating Gate Voltage Oscillations During Short Circuit

In this paper, the impact of the p-n-p bipolar transistor gain on the short-circuit behavior of high-voltage trench insulated-gate bipolar transistors (IGBTs) is analyzed. The short-circuit ruggedness against high-frequency oscillations is strongly improved by increasing the hole current supplied by the collector. By doing so, the electric field at the emitter of the IGBT is increased and less influenced by the amount of the excess charge (i.e., the electric field is fixed). The charge-field interactions during the short circuit event, leading to periodic charge storage and charge removal effect and provoking miller capacitance variations, can be mitigated. The effectiveness of using IGBTs with a high bipolar gain is validated through both simulations and experiments, also a design rule to tradeoff the IGBT’s losses and short-circuit robustness is provided.

Ultrathin Ni12P5 nanoplates for supercapacitor applications

Ultrathin single crystalline nanoplates of Ni12P5 are synthesized via a facile, template-free, wet chemical method. The thickness is about 6 nm with sizes tunable from 5 to 50 nm. The exposed plate surface is formed of {2¯11} lattice plane. Benefitting from the high electrical conductivity and the two dimensional (2D) nanostructures, the Ni12P5 nanoplates exhibit excellent supercapacitor properties. The specific capacity is about 697 C/g at the current density of 1 A/g. Even at 20 A/g, it is measured as 446 C/g, with 64.0% retention indicating an outstanding rate capability. The charge storage mechanisms include a battery-type behavior related to the bulk redox processes and a double-layer capacitance arising from the 2D geometric morphology. In particular, the morphological effects accounts for about 63% of the total charge storage effects at the voltage sweep rate of 2 mV/s in the cyclic voltammetry measurement, and is even higher percentage-wise at a higher sweep rate. This is, by far, the best performance with facile synthesis techniques for single crystalline nickel phosphides.

Improving the Short-Circuit Reliability in IGBTs: How to Mitigate Oscillations

In this paper, the oscillation mechanism limiting the ruggedness of insulated gate bipolar transistors (IGBTs) is investigated through both circuit and device analysis. The work presented here is based on a time-domain approach for two different IGBT cell structures (i.e., trench-gate and planar), illustrating the two-dimensional effects during one oscillation cycle. It has been found that the gate capacitance varies according to the strength of the electric field near the emitter, which in turn leads to charge-storage effects associated with low carrier velocity. For the first time, it has been discovered that a parametric oscillation takes place during the short circuit in IGBTs, whose time-varying element is the Miller capacitance, which is involved in the amplification mechanism. This hypothesis has been validated through simulations and its mitigation is possible by increasing the electric field at the emitter of the IGBT with the purpose of counteracting the Kirk effect.

THERMAL OXIDATION EFFECT ON ELECTRICAL PROPERTIES OF MOS CAPACITORS WITH EMBEDDED Ge NANOCRYSTALS

A 2D layer of spherical, crystalline Ge nanodots embedded in a SiO 2 layer was formed by low pressure chemical vapor deposition combined with furnace oxidation and rapid thermal annealing. The samples were characterized structurally by using transmission electron microscopy in plan-view and cross-section geometries. It was found that the formation of highdensity Ge dots took place due to oxidation induced by the Ge segregation. Electrical properties were controlled by measuring C–V and I–V characteristics after the formation of MOS capacitors in different oxidation conditions and the ambient medium. A strong evidence of the charge storage effect on the crystalline Ge-nanodot layer was demonstrated by the hysteresis behavior of the high-frequency C–V curves. It is shown that dry oxidation followed by its reduction increases the hysteresis value compared to wet oxidation conditions. This hysteresis behavior is discussed taking into account the decrease in the Ge concentration and a possible effect of low temperature GeO evaporation is followed by wet oxidation.

Electronic properties and charge storage effect of amorphous SiN passivated nanocrystalline silicon

Nanocrystalline Si (nc-Si) with mean size of about 4 nm embedded in amorphous SiN film was prepared by annealing Si-rich amorphous SiN film. The film compositions and microstructures were revealed by x-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. It was found the room temperature conductivity is increased from 7 × 10−9 to 1 × 10−5 S/cm due to the formation of nc-Si. The carrier transport process of nc-Si embedded in amorphous SiN matrix is dominated by trap-assisted tunneling mechanism. Moreover, by forming a-SiN0.81/nc-Si(SiN)/a-SiN0.81 sandwiched floating gate structures, both electron and hole can be injected and stored in nc-Si by controlling the applied bias polarity. A large memory window up to about 7 V was observed, and the stored carrier density was about 1012 cm−2. Our experimental results suggested that the interface states of nc-Si can be well passivated by the amorphous SiN matrix, which results in the good charge storage effect.