Junction Rectification Research Articles

Continuous Modulation of Electrocatalytic Oxygen Reduction Activities of Single‐Atom Catalysts throughp‐nJunction Rectification

AbstractFine‐tuning single‐atom catalysts (SACs) to surpass their activity limit remains challenging at their atomic scale. Herein, we exploitp‐type semiconducting character of SACs having a metal center coordinated to nitrogen donors (MeNx) and rectify their local charge density by ann‐type semiconductor support. With iron phthalocyanine (FePc) as a model SAC, introducing ann‐type gallium monosulfide that features a low work function generates a space‐charged region across the junction interface, and causes distortion of the FeN4moiety and spin‐state transition in the FeIIcenter. This catalyst shows an over two‐fold higher specific oxygen‐reduction activity than that of pristine FePc. We further employ three othern‐type metal chalcogenides of varying work function as supports, and discover a linear correlation between the activities of the supported FeN4and the rectification degrees, which clearly indicates that SACs can be continuously tuned by this rectification strategy.

Continuous Modulation of Electrocatalytic Oxygen Reduction Activities of Single-Atom Catalysts through p-n Junction Rectification.

Fine-tuning single-atom catalysts (SACs) to surpass their activity limit remains challenging at their atomic scale. Herein, we exploit p-type semiconducting character of SACs having a metal center coordinated to nitrogen donors (MeNx ) and rectify their local charge density by an n-type semiconductor support. With iron phthalocyanine (FePc) as a model SAC, introducing an n-type gallium monosulfide that features a low work function generates a space-charged region across the junction interface, and causes distortion of the FeN4 moiety and spin-state transition in the FeII center. This catalyst shows an over two-fold higher specific oxygen-reduction activity than that of pristine FePc. We further employ three other n-type metal chalcogenides of varying work function as supports, and discover a linear correlation between the activities of the supported FeN4 and the rectification degrees, which clearly indicates that SACs can be continuously tuned by this rectification strategy.

Fast ionic conduction and rectification effect of NaCo0.5Fe0.5O2-CeO2 nanoscale heterostructure for LT-SOFC electrolyte application

Heterostructure electrolytes made of semiconductor and ionic conductor have drawn significant attention in solid oxide fuel cells (SOFCs) field owing to their attractive ionic conductivity at low operating temperatures. In this study, a new heterostructure is proposed by introducing a layered semiconductor NaCo0.5Fe0.5O2 (NCF) into fluorite structure ionic oxide CeO2 for SOFC electrolyte uses. The prepared samples are characterized in views of phase structure, surface and interface property, and electrical conductivity, followed by being applied in SOFCs for performance, impedance spectra and durability assessment. It is found the NCF-CeO2 forms nanoscale heterostructure with massive hetero-interfaces and enriched oxygen vacancies. The best-performing sample 35NCF-65CeO2 gains improved ionic conduction and promising SOFC performance with power density of 68–1010 mW cm-2 at 350–550 °C. Moreover, durability measurement verifies the NCF-CeO2 based SOFC can be stably operated for 160 h under fixed current density of 100 mA cm-2, whereas there is an obvious degradation in the initial 5 h. A particular attention is paid to investigate the dynamic electrochemical process and junction rectification effect of the NCF-CeO2 cell to interpret the degradation behaviour. Our findings thus certify the great promise of layered and fluorite oxide based NCF-CeO2 nanoscale heterostructure for low-temperature SOFC electrolyte uses.

High-densities of free holes in homoepitaxial n-GaN induced by fluorine-plasma ion implantation

In this work, fluorine plasma ion implantation is used to induce high densities of free holes in homoepitaxial n-GaN for the first time, as evidenced by electroluminescence and p-n junction rectification. F+ ions implanted into the near-surface layer capture electrons from shallow bulk donors, bending the band upward until a high density of free holes is induced at the valence band maximum, and surface donors, depinning the Fermi level to form p-type ohmic contact. Free holes tunnel from the metal into states at the valence band maximum, where they form a conductive p-type channel, benefitting the development of GaN-based junction devices.

Analysis of the generation mechanism of the S-shaped J–V curves of MoS2/Si-based solar cells

Amorphous–microcrystalline MoS2 thin films are fabricated using the sol-gel method to produce MoS2/Si-based solar cells. The generation mechanisms of the S-shaped current density–voltage (J–V) curves of the solar cells are analyzed. To improve the performance of the solar cells and address the problem of the S-shaped J–V curve, a MoS2 film and a p+ layer are introduced into the front and back interfaces of the solar cell, respectively, which leads to the formation of a p–n junction between the p-Si and the MoS2 film as well as ohmic contacts between the MoS2 film and the ITO, improving the S-shaped J–V curve. As a result of the high doping characteristics and the high work function of the p+ layer, a high–low junction is formed between the p+ and p layers along with ohmic contacts between the p+ layer and the Ag electrode. Consequently, the S-shaped J–V curve is eliminated, and a significantly higher current density is achieved at a high voltage. The device exhibits ideal p–n junction rectification characteristics and achieves a high power-conversion efficiency (CE) of 7.55%. The findings of this study may improve the application of MoS2 thin films in silicon-based solar cells, which are expected to be widely used in various silicon-based electronic and optical devices.

二维层状材料异质结光电探测器研究进展（特邀）

Since the era of graphene, two-dimensional layered materials (2DLMs) with distinctive physical, chemical and optoelectronic properties have attracted extensive attention from researchers worldwide. Benefiting from the diversity of material composition and the layer number dependence of their bandgap, the spectral response ranges of 2DLMs can cover an extremely wide band from ultraviolet to infrared radiation. Moreover, because of the lifting of the restriction on lattice matching, 2DLMs can be stacked with other dimensional materials, such as bulk materials, nanowires, and quantum dots, through van der Waals (vdWs) forces, creating unique and exclusive devices from integrated structures. This article reviewed the research progress of several typical 2DLMs heterojunction photodetectors with great potential application in the field of photodetection, focusing on the breakthrough results achieved in performance improvements such as device gain, junction rectification ratio, response time and detection wavelength coverage for devices based on tungsten diselenide (WSe2), arsenic phosphorus (AsP), niobium trisulfide (NbS3) and palladium diselenide (PbSe2), through innovations in heterostructure building and exploitation of 2D processing cutting-edge technology. Meanwhile, we had also briefly analyzed the current challenges confronted by these device researches, and tentatively forecasted its future development trend.

Enhancement of Interfacial Charge Transportation Through Construction of 2D–2D p–n Heterojunctions in Hierarchical 3D CNFs/MoS2/ZnIn2S4 Composites to Enable High‐Efficiency Photocatalytic Hydrogen Evolution

Hierarchical three‐dimensional (3D) carbon nanofibers (CNFs)/molybdenum disulfide (MoS2)/ZnIn2S4 composites with p–n heterojunctions between the basal planes of two‐dimensional (2D) phases are fabricated, using in situ spinning‐based chemical vapor deposition together with hydrothermal processing. It is found that large and intimately interfaced 2D–2D planes between the n‐type ZnIn2S4 and the CNFs‐supported p‐type MoS2 enable evident junction rectification effect, which facilitates interfacial charge separation to assist effective suppression of the recombination of photogenerated electrons and holes. In addition, the p‐type MoS2 nanosheets with high in‐plane conductivity and narrower bandgap are highly effective in providing larger quantities of photoinduced electrons, which can be readily injected into the outer n‐type ZnIn2S4 coating for the reduction of H2O into H2, whereas the holes are driven into the CNF cores by the junction field to be finally scavenged. The large specific surficial area of the sulfides provides abundant sulfur‐rich sites active for H2 evolution. Consequently, the optimal CNFs/MoS2/ZnIn2S4 composite with 5 mmoL MoS2 loading exhibits robust H2 evolution under simulate sunlight irradiation, achieving a remarkably enhanced photocatalytic H2 production rate over 151.42 mmoL⋅h−1⋅g−1 and a high apparent quantum yield of 20.88% at 365 nm, which is 4.65 times higher than that of pristine ZnIn2S4.

Dual origin of room temperature sub-terahertz photoresponse in graphene field effect transistors

Graphene is considered as a promising platform for detectors of high-frequency radiation up to the terahertz (THz) range due to its superior electron mobility. Previously, it has been shown that graphene field effect transistors (FETs) exhibit room temperature broadband photoresponse to incoming THz radiation, thanks to the thermoelectric and/or plasma wave rectification. Both effects exhibit similar functional dependences on the gate voltage, and therefore, it was difficult to disentangle these contributions in previous studies. In this letter, we report on combined experimental and theoretical studies of sub-THz response in graphene field-effect transistors analyzed at different temperatures. This temperature-dependent study allowed us to reveal the role of the photo-thermoelectric effect, p-n junction rectification, and plasmonic rectification in the sub-THz photoresponse of graphene FETs.

P−n Junction Rectifying Characteristics of Purely n -Type GaN-Based Structures

In semiconductor physics, conventional $p-n$ junctions are bipolar, featuring of both $p$- and $n$-type carriers ($i.e.$ holes and electrons). In this study, $p-n$ junction rectification is achieved with $u\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}r$, purely $n$-type (Al,In)GaN structures. This is significant, as the direct-gap group-$I\phantom{\rule{0}{0ex}}I\phantom{\rule{0}{0ex}}I$ nitrides offer the most viable approach to high-frequency, high-power electronics, yet progress has been thwarted by the high resistivity of $p$-type GaN, which is totally absent from the authors' device. Furthermore, their approach can be used for other strongly polarized semiconductors, such as ZnO.

Electronic properties and potential applications of the heterojunction between silicon and multi‐nanolayer amorphous selenium

The electronic properties of the junction formed between multi-nanolayer amorphous selenium and silicon are studied. The current–voltage (I–V) relationship of this type of junction was characterised and the result showed pn junction rectification. Capacitance–voltage (C–V) measurements were also used to obtain the value of the diffusion potential of the junction. From these data, the ideality factor and built-in potential were evaluated. The results show potential in the application of amorphous selenium and silicon as materials in tandem photovoltaic cells and in wide spectral range photodetectors.

Measurement and understanding of single-molecule break junction rectification caused by asymmetric contacts.

The contact effects of single-molecule break junctions on rectification behaviors were experimentally explored by a systematic control of anchoring groups of 1,4-disubstituted benzene molecular junctions. Single-molecule conductance and I-V characteristic measurements reveal a strong correlation between rectifying effects and the asymmetry in contacts. Analysis using energy band models and I-V calculations suggested that the rectification behavior is mainly caused by asymmetric coupling strengths at the two contact interfaces. Fitting of the rectification ratio by a modified Simmons model we developed suggests asymmetry in potential drop across the asymmetric anchoring groups as the mechanism of rectifying I-V behavior. This study provides direct experimental evidence and sheds light on the mechanisms of rectification behavior induced simply by contact asymmetry, which serves as an aid to interpret future single-molecule electronic behavior involved with asymmetric contact conformation.

Double-layer fabrication of cubic-manganites/hexagonal-ZnO on various substrates by ion beam sputtering, and variable electrical property

Hetero double-layers of LaBaMnO3 (LBMO)/ZnO were fabricated by ion beam sputtering on substrates of MgO, sapphire (SP), LaAlO3 (LAO), and SrTiO3 (STO). All the surfaces of substrates, ZnO and LBMO have step-terrace morphology. The p-LBMO/n-ZnO/SP shows junction rectification at different temperatures. The junction resistance follows from colossal magnetoresistance (CMR) of LBMO based on DEC model. The different LBMO/ZnO junctions on the different substrates show different junction behaviors at room temperatures. LBMO/ZnO/STO has the largest rectification factor of 210. After running measurement currents, LBMO/ZnO/STO shows current–voltage (I–V) switchings. LBMO/ZnO/MgO shows very clear switching and large hysteresis between upward and downward voltage sweeps. These are interpreted by CMR and DEC model, and phase separation. The switching is caused by disconnection of percolation path consisting of ferromagnetic metallic grains. The higher resistant state cannot be quickly transformed back to the lower resistant state during the downward sweep.

Dependence of the optoelectronic properties of selenium-hyperdoped silicon on the annealing temperature

Selenium-hyperdoped silicon was prepared by ion implantation at 100eV to a dose of 6×1015Se/cm2, followed by furnace annealing at 500–900°C for 30min. A phase transition from amorphous to crystalline was observed for the sample annealed at 600°C. Carrier density in the Se doping layer gradually increases with the annealing temperature and a high carrier/donor ratio of 7.5% was obtained at 900°C. The effects of annealing temperature on the rectifying behavior and external quantum efficiency of n+p junctions formed on Se-hyperdoped silicon were also investigated. We found that 700°C was the optimal annealing temperature for improving the crystallinity, below-bandgap absorption, junction rectification and external quantum efficiency of Se-doped samples.

Mechanisms behind efficiency droop and degradation in InGaN/GaN LEDs

AbstractThe results of low frequency noise studies in power blue InGaN/GaN LEDs with external quantum efficiency 30‐45% classified by leakage current (LC) values before and after degradation are reported. The LC values at V< 2V integrally characterize electrical properties of extended defect system (EDS) that is typical for InGaN/GaN LEDs. The smaller concentration of extended defects and length of dilatation, dislocation boundaries, the lower LC value is. It has been demonstrated that non‐radiative recombination processes (NRRP) localized in extended defect system (EDS) contribute in efficiency droop of LEDs at j ≥ 10 A/cm2. The main characteristics of degradation processes such as: (1) increase in tunneling current values related with EDS, at U ≤ 2 V, (2) strong deterioration of p‐n junction rectification properties, (3) formation of conductive paths along EDS; (4) increase in non‐uniformity of current distribution, and (5) the formation of local overheating channels at j > 10 A/cm2 along EDS had been revealed. The NRRP are localized along EDS and can be considered as a general mechanism of efficiency droop and the ambiguous degradation process in power InGaN/GaN LEDs (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electronic states at the interface between indium tin oxide and silicon

Electronic properties and thermal stability of interfacial states between indium tin oxide (ITO) and monocrystalline silicon (Si) have been investigated. ITO films with thicknesses of about 300 nm were deposited by dc magnetron sputtering on n- and p-type (100) Si at room temperature. The samples were then annealed for 30 min at different temperatures in the range 100–600 °C, and the ITO-Si junction was found to exhibit rectifying behavior. Current-voltage (IV), capacitance-voltage (CV), and deep-level transient spectroscopy (DLTS) measurements have been used to electrically characterize the ITO-Si interface. DLTS measurements on p-type Si samples reveal a dominant hole trap at around 0.37 eV above the valence band edge. In the n-type samples, a broad band of electron traps occur in the range 0.1-0.2 eV below the conduction band edge. These electron traps display wide DLTS peaks, indicating a band of electronic energy levels rather than well-defined states originating from isolated point defects. All the traps in both the p- and n-type samples are found to be located near the ITO-Si interface. Investigations of the thermal stability of the observed electronic states show that the dominant hole trap anneal out after 30 min at 250 °C, while the dominant electron traps can be stable up to 500 °C. IV and DLTS measurements demonstrate a clear correlation between the annealing of the dominant electronic states and increase in the junction rectification.

PN junction rectification in electrolyte gated Mg-doped InN

PN junction rectification is demonstrated in indium nitride. The junction is formed between the n-type surface accumulation layer and the Mg-doped, p-type bulk in a top-contacted thin film structure. The parasitic shorting path between the top contacts is controlled by gating with an electrolyte. For positive gate voltages, electrons accumulate at the surface and the current flows preferentially through n type regions, and linear current-voltage (I-V) behavior is observed. However, for negative gate voltages, surface electrons are depleted and current flows through the p-type bulk. This creates an n-p-n structure and a characteristic non-linear I-V curve is observed.

The effect of rectifying gap junctions on phase-locking in neuronal networks

Introduction Gap junction mediated electrical coupling is ubiquitous in neuronal systems. Electrical coupling is almost always modeled as a linear ohmic resistance between cells, where the coupling current is proportional to the transjunctional potential. However, many gap junctions exhibit rectification with transjunctional voltage [1]. That is, the coupling conductance attenuates for increased voltage differences between cells. This rectification process can evolve at different time scales. Because gap junction rectification alters the strength of coupling between cells in a way that depends on the intrinsic states of the cells, it may affect the dynamics in neuronal networks. However, the effects of rectification on network dynamics are largely unstudied.

The photoluminescence properties of ZnO:N films fabricated by thermally oxidizingZn3N2 films using plasma-assisted metal-organic chemical vapour deposition

Nitrogen doped ZnO films are directly fabricated by the thermal oxidation ofZn3N2 films. Zn3N2 films are prepared by plasma-assisted metal-organic chemical vapour deposition(PA-MOCVD). By comparing with undoped ZnO photoluminescence spectra, amuch stronger bound exciton emission due to a neutral nitrogen acceptor(A0X) is observed at low temperature. The neutral acceptor level is located at 130 meV above thevalence band maximum. To demonstrate the quality of ZnO:N thin films as a p-type, aZn3N2/n-Si heterojunction structure was first fabricated. With an increase of oxidation temperature,the structure has gradually shown p–n junction rectification characteristics fromI–V measurements.

Heat flow asymmetry on a junction of quartz with graphite

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Electrical Properties of Gallium Antimonide

Data are presented on the conductivity and Hall coefficient of several samples of GaSb over the temperature from -196\ifmmode^\circ\else\textdegree\fi{}C to 650\ifmmode^\circ\else\textdegree\fi{}C. The lowest room-temperature conductivity obtained was 12 ${\mathrm{ohm}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. All material produced from zone-purified components was $p$-type. $N$-type material was produced by doping with tellurium, as were $p\ensuremath{-}n$ junctions. The intrinsic band gap is estimated from junction rectification data to be 0.78 ev at -196\ifmmode^\circ\else\textdegree\fi{}C. The mobility of electrons was found by measurement on $n$-type material to be several times greater than the hole mobility. The mobilities of both holes and electrons are found to vary approximately as ${T}^{\ensuremath{-}\frac{3}{2}}$ in the lattice scattering range.