Hole Storage Research Articles

Suppressed gate leakage and enlarged gate over-drive window of E-mode p-GaN gate double channel HEMTs

A 600-V p-GaN gate double channel HEMT (DC-HEMT) is presented with a systematic investigation of the gate characteristics, including the leakage current, breakdown, and reliability under forward bias stress. It is found that the gate leakage of the DC-HEMT is substantially lower than that of the p-GaN single channel HEMT (SC-HEMT) owing to suppressed electron spillover that stems from hole storage in the quantum well upper channel. Consequently, the gate breakdown voltage of the DC-HEMT is improved to 14.7 V compared to 12.2 V of the SC-HEMT. Besides, the gate operating voltage margin of the DC-HEMT is expanded to 4.2 V compared to 3.3 V of the SC-HEMT according to the gate lifetime evaluation.

Synergistic effect of FeOOH cocatalyst and Al2O3 passivation layer on BiVO4 photoanode for enhanced photoelectrochemical water oxidation

BiVO4 is one of the most attractive photoanodes for water oxidation due to its 2.4 eV narrow band gap, suitable band edge position, good stability in aqueous solution, low cost and non-toxicity. However, due to some inherent disadvantages such as low carrier mobility, severe charge recombination and slow water oxidation kinetics, the actual BiVO4 photocurrent density is often lower than the theoretical value of 7.5 mA cm−2. In this paper, BiVO4 was modified by alkali-treated Al2O3 passivation layer and FeOOH, and the photocurrent density of BiVO4 reached an astonishing 3.8 mA cm−2 at 1.23 VRHE, and the ABPE (applied bias photon-to-current efficiency) was close to 1 %. The detailed structural characterization and electrochemical test show that Al2O3 prepared by ALD (atomic layer deposition) can play a role in passivation of BiVO4 surface state after alkali treatment, inhibit electron hole recombination on BiVO4 surface, and accelerate hole transfer. As a hole storage layer and catalyst layer, FeOOH promoted the interfacial hole transfer, increased the active sites at the electrode electrolyte interface, and significantly increased the water oxidation activity. This work provides a novel method to enhance the performance of water electrolysis by using ALD to assist passivation of bismuth vanadate photoanode surface states.

Structurally ordered FeCo@FeCoOx@NC dual-shell nanoparticles synthesized under micro-oxygen conditions: An efficient cocatalyst for BiVO4 photoelectrochemical water oxidation

Electrocatalysts are usually integrated onto light-absorbing semiconductors to form efficient photoelectrochemical water-splitting systems. Transition metal oxide nanoparticles serve as excellent electrocatalysts, but exhibit poor performance as cocatalysts for photoelectrodes. To address this issue, a FeCo@FeCoOx@NC dual-shell nanoparticle (consisting of a FeCo alloy core, an intermediate FeCoOx shell, and an outermost graphitic carbon shell) was prepared under micro-oxygen conditions. The FeCo alloy has the dual functions of rapid hole storage and efficient charge transport, while the FeCoOx layer acts as active sites to accelerate the kinetics of the water oxidation reaction and the graphitic carbon protects the internal structure of the nanoparticles. Under the synergistic effect of FeCo@FeCoOx@NC and NiFeOx cocatalysts, the injection efficiency and separation efficiency of BiVO4 photoanode almost reach 100 %, and the photocurrent density reaches 6.85 mA cm−2 (1.23 VRHE, AM 1.5 G), marking the highest reported value to date.

Expediting Photo‐Charging of Semiconductors through a Bipolar Charge Storage Junction for Responsive Dark Photocatalysis

AbstractPhoto‐charging of semiconductors stores electrons for decoupled solar utilization, overcoming intermittent sunlight availability. However, the sluggish photo‐charging process impedes responsive charge storage. Herein, a bipolar charge storage junction is demonstrated to expedite the photo‐charging process within a renowned ionic‐CN/Co3O4 configuration, benefiting from their mismatched photo‐charging kinetics. Rapid photo‐hole storage associated with structural evolution at geometrically dependent Co sites in Co3O4 improves sluggish electron storage for ionic‐CN, while slow recovery of altered [CoO4] and [CoO6] structures delayed electron‐hole recombination. By passivating individual atomic sites, rapid hole storage is attributed to synergistic contributions of tetrahedral Co2⁺ and octahedral Co3⁺ species. The bipolar charge storage junction is photo‐charged at 0.86 A g−1, rivaling the electrical charging rate in ion batteries. With 60 s photo‐charging, the junction yields 0.27 mmol g−1 of “dark” hydrogen, the benchmark for such a short photo‐charging timeframe. This proof‐of‐concept design empowers the fast photo‐charging ability of bipolar charge storage junctions, advancing responsive photo‐charge storage for decoupled solar utilization.

Low-energy and tunable LIF neuron using SiGe bandgap-engineered resistive switching transistor

We have proposed leaky integrate-and-fire (LIF) neuron having low-energy consumption and tunable functionality without external circuit components. Our LIF neuron has a simple configuration consisting of only three components: one bandgap-engineered resistive switching transistor (BE-RST), one capacitor, and one resistor. Here, the crucial point is that BE-RST with a silicon–germanium heterojunction possesses an amplified hysteric current switching with a low latch-up voltage due to improved hole storage capability and impact ionization coefficient. Therefore, the proposed neuron utilizing BE-RST requires an energy consumption of 0.36 pJ/spike, which is approximately six times lower than 2.08 pJ/spike of pure silicon-RST based neuron. In addition, the spiking properties can be tuned by modulating the leakage rate and threshold through gate bias, which contributes to energy-efficient sparse-activity and high learning accuracy. As a result, our proposed neuron can be a promising candidate for executing various spiking neural network applications.

Dual Hole Transport Layers Heterojunction and Band Alignment Engineered Mo:BiVO4 Photoanodes for Efficient Water Splitting.

BiVO4-based photoanode is one of the most promising photoanodes for photoelectrocatalytic water splitting. However, the serious problem of interface charge recombination limits its further development. Here, a Mo:BiVO4/NiOx/CPF-TCzB/NiCoBi photoanode is constructed with double hole transport layer and an energy level gradient to achieve an effective photo-generated holes extraction and accumulation at the surface electrocatalyst. The conjugated polycarbazole framework CPF-TCzB is used as hole transport layer to eliminate the charge recombination center between Mo:BiVO4 and NiCoBi electrocatalyst and realize the extraction and storage of photo-generated hole; NiOx nanoparticles are further inserted between Mo:BiVO4 and CPF-TCzB to form a gradient energy level, eliminating the energy level barrier and optimizing band alignment. As a result, Mo:BiVO4/NiOx/CPF-TCzB/NiCoBi achieves a much higher photocurrent densities of 3.14mA cm-2 than that of Mo:BiVO4 (0.42mA cm-2) at 0.6V versus RHE. This work provides an specific way to adjust the band structure of BiVO4-based photoanodes and realize efficient hole extraction and storage for PEC water splitting.

Performance improvement of GaN-based vertical cavity surface emitting laser by employing a hole storage layer and enhancing the carrier transport behavior

In this paper, the transport behavior of carriers between multiple quantum wells (vertical) and inside a single quantum well (radial) in a GaN-based Vertical Cavity Surface Emitting Laser (VCSEL) is investigated, and a new device structure with a hole storage layer is proposed to enhance the laser performance. The theoretical results indicate that the vertical transport capability of holes is the key factor for total stimulated recombination rate and hole leakage. The VCSEL with a double-QW structure exhibits better output performance compared to the devices with three or more QWs owing to the lower light absorption loss and the stronger optical field in the active region. Furthermore, a thicker undoped GaN layer is proposed to be added as the hole storage layer to mitigate hole leakage for the VCSEL with a double-QW structure. This new structure can increase the tilt of energy band in the region of the hole storage layer and effectively improve the uniformity of radial distribution of holes in QWs. Therefore, it is beneficial to reduce the threshold current and enhance the laser output power.

Hole transfer layer of glucose-derived carbon enabled rapid charge transfer and hole storage for efficient water splitting

Charge recombination at the interface of oxygen evolution catalyst (OEC) and BiVO4-based photoanode is one of the great challenges to achieve efficient photoelectrochemical (PEC) water splitting due to the poor charge transfer and separation efficiency of BiVO4. Herein, a composite photoanode (NiFe/C-Mo:BiVO4) consisting of a molybdenum doped BiVO4 photoanode, an OEC interfacial layer of NiFeOOH and a tailorable hole transfer layer (HTL) made of glucose-derived carbon in between, was designed and fabricated for highly efficient PEC water splitting. The composite NiFe/C-Mo:BiVO4 photoanode exhibited the photocurrent density of 5.62 mA cm−2 at 1.23 VRHE and an outstanding photo-stability. Characterization and photoelectrochemical analyses revealed that the inserted carbon HTL, though not active for surface water oxidation kinetics, greatly suppressed the unwanted recombination of electron-hole pairs and drastically improved the transfer and storage of charge carriers at the OEC/BiVO4 interface. A surface charge separation efficiency of 89 % at 1.23 VRHE and remarkable hole storage properties were obtained. This work afforded a novel approach to the design of low-cost and sustainable HTL integrated photoanodes for efficient PEC water oxidation.

Memory-Enabled Quantum-Dot Light-Emitting Diodes.

Quantum-dot light-emitting diodes (QLEDs) with memory capability can provide multifunctional integration properties in on-chip and intelligent electronic applications. Herein, memory properties are achieved by inserting a tungsten oxide (WOx) film between the ZnO electron-transporting layer and cathode. Pentavalent tungsten ions (W5+) in this nonstoichiometric WOx film can be oxidized to W6+ by storing holes, inducing significant electrons in the adjacent ZnO layer. Hole storage in the WOx layer suppresses electron injection into the quantum dot emissive layer, hence reducing electroluminescence intensity on the onset stage of the QLEDs. This operation-history correlation for the electroluminescence intensity means a memory behavior for the QLEDs. Furthermore, the power efficiency of the devices is greatly improved after inserting the WOx layer due to electrical field-dependent self-adaptive electron injection into the quantum dots (QDs). We anticipate this type of QLEDs have potential applications in on-chip integration applications, such as the optical computing field and storage.

Grid-patterned trench insulated gate bipolar transistor for 1.2 kV hybrid/plug-in hybrid electric vehicle silicon power devices

This paper reports on the newly developed silicon insulated gate bipolar transistor (IGBT) for Toyota’s fifth generation power devices. The designed IGBTs with a grid-patterned trench provide a lower on-state voltage (V ON ) while maintaining a wide mesa width. A successful 15% reduction of V ON was accomplished by enhancement of the two-dimensional hole storage effect. Furthermore, the grid-patterned trench IGBT merged with Schottky and multi-layered anode technology demonstrated a significant improvement in the trade-off curve between the reverse recovery current (I rr ) and V ON in a reverse conducting IGBT without a lifetime control process. As a result, the grid-patterned trench IGBT has contributed to reduce power loss and volume in the new power control units.

Regulating carrier transfer route via 1D-2D junction on TiO2 nanorods intercalated with N-doped γ-graphyne nanosheets

One-dimensional TiO2 nanostructure has been widely studied in the domain of photoelectrochemical water splitting. Nevertheless, the wide bandgap and fast carriers recombination of TiO2 restrain its performance. In this study, two-dimensional N-doped γ-graphyne nanosheets were synthesized and employed in the reasonable design of TiO2 heterostructure, facilitating carrier migration and water oxidation reaction. The photocurrent density of photoanode composed of N-doped γ-graphyne/TiO2 nanorods reaches 1.48 mA cm−2, 1.72 times that of pristine TiO2 at a bias of 1.23 V (vs. RHE). Meanwhile, the calculated applied bias photon-to-current efficiency increases from 0.25 % to 0.56 %. The combination of TiO2 nanorods with layered semiconductive N-doped γ-graphyne contributes to the construction of charge transfer channels, regulating surface states and reaction sites, promoting the hole storage, and reducing the free energy barrier in the velocity determination process. This study sheds light on the design of N-doped γ-graphyne modified catalysts and facilitates their application in photoelectrochemical and photoelectrocatalytic fields.

Intrinsic Polarized Electric Field Induces a Storing Mechanism to Achieve Energy Storing Catalysis in V2 C MXene.

Efficient storage and separation of holes and electrons pose significant challenges for catalytic reactions, particularly in the context of single-phase catalysis. Herein, V2 C MXene, with its intrinsic polarized electric field, successfully overcomes this obstacle. To enhance hole storage, a multistep etching process is employed under reducing conditions to control the content of surface termination groups, thus exposing more defective active sites. The intrinsically polarized electric field confines holes to the surface of the layer and free electrons within the layer, leading to a lag in e- release compared to h+ . The quantities of stored holes and electrons are measured to be 18.13µmolg-1 and 106.37 µmol g-1 , respectively. Under dark, V2 C demonstrates excellent and stable dark-catalytic performance, degrading 57.91% of tetracycline (TC 40mg L-1 ) and removing 23% of total organic carbon (TOC) after 140 min. In simulated sunlight and near-infrared light, the corresponding degradation rates reach 72.24% and 79.54%, with corresponding TOC removal rates of 49% and 48%, respectively. The hole and electron induced localized surface plasmon resonance (LSPR) effects contribute to a long-lasting and enhanced broad-spectrum mineralization of V2 C MXene. This study provides valuable insights into the research and application of all-weather MXene energy storage catalytic materials.

Hole storage overlayer of amorphous hafnium oxide for boosting hematite-based solar water splitting

Hole storage layer (HSL) has been proved to be effective for constructing highly efficient photoelectrochemical (PEC) systems owing to its timely extraction and temporary storage of the photogenerated holes. Here we demonstrate an ultrathin HSL of amorphous hafnium oxide (HfOx) by a combined strategy of hybrid microwave annealing (HMA) and in-situ Hf doping, which enhances the PEC performance collaboratively: i) in-situ doping of Hf4+ ions into hematite lattices to enhance the electrical conductivity in the bulk; and ii) amorphous HfOx overlayer on hematite surface as a HSL to promote efficient charge separation between electrons and oxidizing equivalents in water oxidation. As a result, the fabricated Hf:Fe2O3 @HfOx nanorod photoanode achieves a photocurrent density of 3.47 mA cm−2 at 1.23 VRHE under simulated sunlight (100 mW cm−2). With NiCoFe(OH)x co-catalyst modification, the photocurrent density further increases to 4.13 mA cm−2 at 1.23 VRHE, which is 3 times higher than that of bare hematite (1.24 mA cm−2) and comparable to the state-of-the-art hematite photoanode performance. This work demonstrates the high potential of the HMA-induced engineering of transition metal oxides applicable to the field of solar energy conversion.

Application fruit tree hole storage brick fertilizer is beneficial to increase the nitrogen utilization of grape under subsurface drip irrigation.

It is very important to promote plant growth and decrease the nitrogen leaching in soil, to improve nitrogen (N) utilization efficiency. In this experiment, we designed a new fertilization strategy, fruit tree hole storage brick (FTHSB) application under subsurface drip irrigation, to characterise the effects of FTHSB addition on N absorption and utilization in grapes. Three treatments were set in this study, including subsurface drip irrigation (CK) control, fruit tree hole storage brick A (T1) treatment, and fruit tree hole storage brick B (T2) treatment. Results showed that the pore number and size of FTHSB A were significantly higher than FTHSB B. Compared with CK, T1 and T2 treatments significantly increased the biomass of different organs of grape, N utilization and 15N content in the roots, stems and leaves, along with more prominent promotion at T1 treatment. When the soil depth was 15-30 cm, the FTHSB application significantly increased the soil 15N content. But when the soil depth was 30-45 cm, it reduced the soil 15N content greatly. T1 and T2 treatments obviously increased the activities of nitrite reductase (NR) and glutamine synthetase (GS) in grape leaves, also the urease activity(UR) in 30 cm of soil. Our findings suggest that FTHSB promoted plant N utilization by reducing N loss in soil and increasing the enzyme activity related to nitrogen metabolism. In addition, this study showed that FTHSB A application was more effective than FTHSB B in improving nitrogen utilization in grapes.

Amorphous FeOOH-mediated directional charges transfer in light-switchable oxygen vacancies BiOBr for boosting photocatalytic oxygen evolution

Directing the transfer of photoinduced charges to various reaction sites through catalyst design plays crucial roles in enhancing photocatalytic oxygen evolution. Herein, we used a facile alcoholysis method to synthesize amorphous FeOOH modified light-switchable oxygen vacancies BiOBr, which exhibited outstanding photocatalytic oxygen evolution activity. Density functional theory calculations, photoelectronchemical tests and kelvin probe force microscopy revealed that FeOOH overlayer acts as the hole storage layer, while oxygen vacancies (OVs) provided a number of electron trap centers. Benefiting from this synergistic effect, the photogenerated charges showed an outstanding directional transfer performance, which greatly prolong the lifetime of the photo-induced charge carriers. Moreover, as a cocatalyst for water oxidation, FeOOH can effectively lower the kinetics barriers and provide more active sites for oxygen evolution reaction. Therefore, under simulated sunlight irradiation, the 2%FeOOH/BiOBr photocatalyst demonstrated remarkable photocatalytic activity towards oxygen evolution, achieving a rate of 284.34 μmol·g−1·h−1, which is around 1.71 folds than pure BiOBr. Finally, the possible reaction mechanism has also been discussed. This work has provided valuable insights and inspiration for the effective design and optimization of BiOBr-based catalysts, which play a critical role in facilitating efficient directional transfer of photogenerated charges.

Citrate modulation of CoAl(OH)x Catalyst/Sb–TiO2 nanorods interface boosting photocarrier separation and injection for enhanced water oxidation

The design of an oxygen evolution catalyst (OEC) coupled photoanode ensuring effective charge separation, transfer, and injection is always desirable for enhanced water oxidation kinetics. Here, we have designed Sb-doped TiO2 nanorods (NRs) photoanode coupled with the ultrathin amorphous CoAl(OH)x OEC via citrate anion bridging. The CoAl(OH)x performs as a hole scavenger OEC, a hole storage layer, surface defect passivation layer, and also generates a band banding leading to the built-in potential at the semiconductor/catalyst interface favoring rapid hole separation. The citrate linking improves the CoAl(OH)x/Sb–TiO2 interfacial bonding and reduces the interfacial impedance to boost the photocarrier separation. Citrate bridging also serves as an efficient hole extraction layer and transportation pathway and promotes oxygen vacancy formation, which favors adsorbing OH− during the OER. As a result, the CoAl(OH)x/cit/Sb–TiO2 NRs photoanode exhibits a superior photocurrent density of 1.73 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (VRHE), close to the theoretical maxima of titanium dioxide, with a very low onset potential of 0.12 VRHE and an extremely high hole injection efficiency of 93.1%. This work demonstrates an effective design strategy to boost the performance of OER catalyst coupled photo harvesting semiconductor photoanodes to achieve efficient solar water splitting.

Integrated solar-rechargeable supercapacitors with a dual-functional-layered electrode

Early integrated solar-rechargeable supercapacitor (ISRS) systems with four physically distinguishable electrodes are cumbersome and require multistep manufacturing process with application disadvantages. Therefore, a stacked ISRS with a three-electrode mode that uses a dual-functional-layered (shared) electrode, which is particularly important to integrate two main active components, is one of the target configurations for a compact, safe and efficient power supplier in advanced soft electronics. This work reports the effect of various fabrication methods on the surface morphology profile of a graphene oxide-incorporated poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (m-PHGO) as a shared electrode; this process exhibited a significant impact on the charge/discharge rate and ISRS efficiency. By controlling the deposition method, the shared electrode fabricated by a modified spin/spray-coating technique using an m-PHGO dispersion features an interface that meets all of the requirements of a dual-functional layer. It is effective for hole charge filtration, transfer, and storage in the stacked ISRS. Under 1-sun illumination, the supercapacitor moiety is charged entirely by the organic solar cell unit within 5 s to build a fusion ISRS capable of approaching a high charging voltage of ∼0.6 V. The as-developed ISRS (with a thickness of ∼2.6 μm and the substrate) shows an impressive energy-storage efficiency of ∼81%. This study provides insights about fabricating high-performance and easy-to-use compact electronic devices.

An integrated solar battery based on a charge storing 2D carbon nitride.

Solar batteries capable of harvesting sunlight and storing solar energy present an attractive vista to transition our energy infrastructure into a sustainable future. Here we present an integrated, fully earth-abundant solar battery based on a bifunctional (light absorbing and charge storing) carbon nitride (K-PHI) photoanode, combined with organic hole transfer and storage materials. An internal ladder-type hole transfer cascade via a transport layer is used to selectively shuttle the photogenerated holes to the PEDOT:PSS cathode. This concept differs from previous designs such as light-assisted battery schemes or photocapacitors and allows charging with light during both electrical charge and discharge, thus substantially increasing the energy output of the cell. Compared to battery operation in the dark, light-assisted (dis)charging increases charge output by 243%, thereby increasing the electric coulombic efficiency from 68.3% in the dark to 231%, leading to energy improvements of 94.1% under illumination. This concept opens new vistas towards compact, highly integrated devices based on multifunctional, carbon-based electrodes and separators, and paves the way to a new generation of earth-abundant solar batteries.

Dynamic charge collecting mechanisms of cobalt phosphate on hematite photoanodes studied by photoinduced absorption spectroscopy.

Reaction sites, surface states, and surface loaded electrocatalysts are photoinduced charge storage sites and critical to photoelectrochemical (PEC) performance, however the charge transfer mechanisms involved in the three remain poorly understood. Herein, we studied the charge transfer processes in hematite (Fe2O3) without/with loaded cobalt phosphate (CoPi) by operando photoinduced absorption (PIA) spectroscopy. The loaded CoPi receives trapped holes in surface states at low potential and directly captures holes in the valence band at high potential. Through the dynamic hole storage mechanisms, loaded CoPi on Fe2O3 facilitates spatial charge separation and serves as a charge transfer mediator, instead of serving as a catalyst to change the water oxidation mechanism (constant third-order reaction). The spatial separation of photoinduced charges between Fe2O3 and CoPi results in more long-lived holes on the Fe2O3 surface to improve PEC water oxidation kinetically. The dynamic charge collecting mechanism sheds light on the understanding and designing of electrocatalyst loaded photoanodes.

Hole Storage Interfacial Regulation of Sb2Se3 Photocathode with Significantly Enhanced Photoelectrochemical Performance.

Although interfacial engineering materials for antimony selenide (Sb2Se3) photocathodes have been intensively studied, most of the previous research has focused on the development of photogenerated electron transfer promoters. In this work, Sb2Se3 photocathodes are innovatively modified by using ferrihydrite (Fh), which has been widely used as a hole storage layer in photoanodes. After modifying Fh, the photocurrent density of the Sb2Se3 photocathode was increased from -0.27 to -1.6 mA cm-2 at 0 VRHE with the onset potential positive shift about 150 mV, and an impressive injection efficiency of 83.84% was achieved. The major contribution of Fh to the photoelectrochemical (PEC) performance enhancement was demonstrated by various characterization studies. The results show that the enhancement performance of PEC is largely attributed to the capture of back-migrating holes by Fh, the reduction of interfacial charge transfer resistance, and the significant increase in electrochemical active surface area (ECSA). This work presents new insights into the application of hole storage layers in Sb2Se3-based photocathodes.