P-n Junction Research Articles

Improved performance in MoS2 homogeneous junction field effect transistors by optimizing electrodes contact

Junction field effect transistor (JFET) operates by controlling the thickness of depletion layer in channel with a reverse biased pn junction without dielectric issues, leading to high performance in nanoscale. Two-dimensional MoS2 has shown excellent electronic properties in atomic scale. MoS2 is an n-type semiconductor, therefore JFET based on MoS2 either adopts heterogeneous structure or doping of MoS2 needs to be done. Heterogeneous JFET suffers from lattice mismatching and other interface limitations. Homogeneous JFET with stable doping stands out. Herein, we propose a homogeneous JFET with stable doping by toroidal-magnetic-field controlled nitrogen plasma. The gate-channel pn homojunction in JFET exhibits excellent pn diode rectifying behavior with low reverse current. This JFET shows n-channel characteristics, and by improving contact between electrodes and MoS2, 102 improvement in mobility is demonstrated. The ON/OFF ratio reaches 104 in optimized JFETs.

The intercalated disc: a unique organelle for electromechanical synchrony in cardiomyocytes.

The intercalated disc (ID) is a highly specialized structure that connects cardiomyocytes via mechanical and electrical junctions. Although described in some detail by light microscopy in the 19th century, it was in 1966 that electron microscopy images showed that the ID represented apposing cell borders and provided detailed insight into the complex ID nanostructure. Since then, much has been learned about the ID and its molecular composition, and it has become evident that a large number of proteins, not all of them involved in direct cell-to-cell coupling via mechanical or gap junctions, reside at the ID. Furthermore, an increasing number of functional interactions between ID components are emerging, leading to the concept that the ID is not the sum of isolated molecular silos but an interacting molecular complex, an "organelle" where components work in concert to bring about electrical and mechanical synchrony. The aim of the present review is to give a short historical account of the ID's discovery and an updated overview of its composition and organization, followed by a discussion of the physiological implications of the ID architecture and the local intermolecular interactions. The latter will focus on both the importance of normal conduction of cardiac action potentials as well as the impact on the pathophysiology of arrhythmias.

The transparent Mg:NiO/SnO2 pn junctions toward photovoltaic conversion enhancement via the potential regulation of Mg-doping

The transparent Mg:NiO/SnO2 pn junctions toward photovoltaic conversion enhancement via the potential regulation of Mg-doping

The enhanced photocatalytic performance of Co3O4 nanoparticles/In2O3 nanotubes pn junction via dual MOFs template auxiliary

The enhanced photocatalytic performance of Co3O4 nanoparticles/In2O3 nanotubes pn junction via dual MOFs template auxiliary

Simulation Study to Enhance the Efficiency of Switching Devices using the Combinations of Diodes in Various Networks

AbstractIn this communication, PSpice simulation software is used to design and characterize reverse biasing modes in series and parallel combinations. Using multiple diodes of similar types, how the breakdown voltage and power dissipation vary in parallel and series modes in reverse bias is investigated. In this paper, correlation equations and correlation factors between voltage and current in both series and parallel combinations using n = 1‐5 diodes in reverse bias are also found. The second‐order correlation equation between voltage and current provides a new way for designing new networks of PN junction diodes for better power gain. The mathematical formulation for applied voltage and average current of n = 1‐10 diodes in parallel and series combinations is also calculated, which can help researchers to design new network circuits for switching devices in the electronics industry.

Molecular Dipole-Modulated Charge Transport across Organic Monolayer-Modified Metal–Semiconductor Junctions

The effect of molecular dipoles on charge transport across organic monolayer-modified metal–semiconductor junctions has been investigated systematically. We have prepared a new set of organic monolayers with varied terminal derivatization on crystalline silicon to construct molecular junctions using mercury drops as the top contact electrode. Although the surface and structural characterization indicated the high quality and uniformity of all these monolayers, the junctions (Hg/R–Si≡) showed a diverse electrical performance. Beyond taking the most common theoretical approach to analyze these molecular junctions, that is, applying the thermionic emission model (TE) to calculate the barrier height (ΦB) and ideality factor (η), we have examined the contribution of the carrier generation–recombination (CGR) mechanism by fitting the experimental current–voltage curves. When η is close to unity, the charge transport across these molecular junctions is dominated by TE; for η values greater than unity, TE indeed remains the dominant current transport pathway, while CGR transport becomes significant.

Light-Driven Ion Transport through Single-Heterojunction Nanopores.

Inspired by natural photosynthesis, light has become an emerging ionic behavior regulator and ion-pumping source. Nanoprocessing technology has allowed the bridge between the light-regulated nanofluids and the optoelectronic properties of two-dimensional (2D) materials, which inspires applications like energy harvesting and enhances fundamental understandings in nanofluidics. However, unlike light-induced ion pumping based on densely layered membranes with multiple nanochannels, experimental implementation on atomically thin materials featuring only a single nanochannel remains challenging. Here, we report light-induced ion pumping based on a single artificial heterojunction nanopore. Under light illumination, the induced current through a single nanopore reaches tens of picoamperes. The hole-electron separation originating from the optoelectrical property of a van der Waals PN junction is proposed to capture the light-driven ion transport. Further, different methods are adopted to modify the ion behavior and response time, presenting potential applications in fluidic photoenergy harvesting, photoelectric ion transport control, and bionic artificial neurons.

Terahertz Nonlinear Hall Rectifiers Based on Spin-Polarized Topological Electronic States in1T-CoTe2.

The zero-magnetic-field nonlinear Hall effect (NLHE) refers to the second-order transverse current induced by an applied alternating electric field; it indicates the topological properties of inversion-symmetry-breaking crystals. Despite several studies on the NLHE induced by the Berry-curvature dipole in Weyl semimetals, the direct current conversion by rectification is limited to very low driving frequencies and cryogenic temperatures. The nonlinear photoresponse generated by the NLHE at room temperature can be useful for numerous applications in communication, sensing, and photodetection across a high bandwidth. In this study, observations of the second-order NLHE in type-II Dirac semimetal CoTe2 under time-reversal symmetry are reported. This is determined by the disorder-induced extrinsic contribution on the broken-inversion-symmetry surface and room-temperature terahertz rectification without the need for semiconductor junctions or bias voltage. It is shown that remarkable photoresponsivity over 0.1 A W-1 , a response time of approximately 710ns, and a mean noise equivalent power of 1 pW Hz-1/2 can be achieved at room temperature. The results open a new pathway for low-energy photon harvesting via nonlinear rectification induced by the NLHE in strongly spin-orbit-coupled and inversion-symmetry-breaking systems, promising a considerable impact in the field of infrared/terahertz photonics.

SYSTEMATIC FIELD APPLICATION OF ENHANCED PLASMONIC ORGANIC SOLAR CELL: AN OVERVIEW

Organic solar cells (OSCs) have attracted considerable research interest due to their satisfactory properties including light-weight, low-cost, low-temperature fabrication process, semi-transparency and mechanical flexibility. Recent advances in OSCs have demonstrated above 10% efficiency in single-junction cells, indicating a strong competitiveness when compared with the commercial silicon photovoltaic system. To obtain maximum efficiency, there is a trade-off between light absorption and charge transport efficiency. Plasmonic light-trapping scheme is a feasible approach to maximize light absorption while maintaining charge transport efficiency. To give an overall look at the plasmonic organic solar cells, we review the recent progress on plasmonic-enhanced OSCs devices by integration with metal plasmonic enhancers, including both experimental and theoretical works. Among the varying proposed plasmonic structures, nano particles are preferable because of their strong scattering properties, particle size tunability, shape, and dielectric environment. In addition, design approaches based on plasmonics can be used to improve absorption in solar cells, permitting a considerable reduction in the physical thickness of solar cell absorber layers, and yielding novel options for solar-cell designs. Also, the simplicity in plasmonics preparation and integration methods is easily compatible with the standard solar cell fabrication process.

Biotin Binding Hardly Affects Electron Transport Efficiency across Streptavidin Solid-State Junctions

The electron transport (ETp) efficiency of solid-state protein-mediated junctions is highly influenced by the presence of electron-rich organic cofactors or transition metal ions. Hence, we chose to investigate an interesting cofactor-free non-redox protein, streptavidin (STV), which has unmatched strong binding affinity for an organic small-molecule ligand, biotin, which lacks any electron-rich features. We describe for the first time meso-scale ETp via electrical junctions of STV monolayers and focus on the question of whether the rate of ETp across both native and thiolated STV monolayers is influenced by ligand binding, a process that we show to cause some structural conformation changes in the STV monolayers. Au nanowire-electrode-protein monolayer-microelectrode junctions, fabricated by modifying an earlier procedure to improve the yields of usable junctions, were employed for ETp measurements. Our results on compactly integrated, dense, uniform, ∼3 nm thick STV monolayers indicate that, notwithstanding the slight structural changes in the STV monolayers upon biotin binding, there is no statistically significant conductance change between the free STV and that bound to biotin. The ETp temperature (T) dependence over the 80-300 K range is very small but with an unusual, slightly negative (metallic-like) dependence toward room temperature. Such dependence can be accounted for by the reversible structural shrinkage of the STV at temperatures below 160 K.

Highly responsive silicon-based hot-electron photodetector with self-aligned metamaterial interdigital electrodes

A sensitive silicon-based hot-electron photodetector based on a self-aligned metal–semiconductor–metal junction is developed. Nearly perfect absorption is achieved with the metamaterial optical coupling, whereas the absorption difference between the upper and lower interdigital gratings is as large as 70% near the resonant wavelength. Arising from the asymmetric photo-absorption, the measured responsivity values of the self-aligned interdigital grating devices reach 1.89 and 0.78 mA/W under zero biasing conditions at the wavelengths of 1310 and 1550 nm, respectively. These values approach the reported record photo-responsivity of hot-electron photodetectors with conventional metal–semiconductor junctions. In addition, the indication of polarity-switchable photocurrent appears due to the wavelength-dependent absorption of the upper and lower metal interdigital gratings. Our device, combining the self-aligned metamaterial interdigital electrodes with highly asymmetric absorption, shows prospects for applications in photodetection, photovoltaics, integrated optoelectronics, and optical communications.

Stable Organic Radical for Enhancing Metal-Monolayer-Semiconductor Junction Performance.

The preparation of monolayers based on an organic radical and its diamagnetic counterpart has been pursued on hydrogen-terminated silicon surfaces. The functional monolayers have been investigated as solid-state metal/monolayer/semiconductor (MmS) junctions showing a characteristic diode behavior which is tuned by the electronic characteristics of the organic molecule. The eutectic gallium-indium liquid metal is used as a top electrode to perform the transport measurements and the results clearly indicate that the SOMO-SUMO molecular orbitals impact the device performance. The junction incorporating the radical shows an almost two orders of magnitude higher rectification ratio (R(|J1V/J-1V|) = 104.04) in comparison with the nonradical one (R(|J1V/J-1V|) = 102.30). The high stability of the fabricated MmS allows the system to be interrogated under irradiation, evidencing that at the wavelength where the photon energy is close to the band gap of the radical there is a clear enhancement of the photoresponse. This is translated into an increase of the photosensitivity (Sph) value from 68.7 to 269.0 mA/W for the nonradical and radical based systems, respectively.

Investigation on performance degradation mechanism of GaN p–i–n diode under proton irradiation

Radiation effects of a 150 keV proton beam with various fluences on GaN-based quasi-vertical p–i–n diodes are investigated. For fundamental analysis, the electrical properties of P-GaN and N−-GaN separated from p–i–n diodes are also investigated. With the increase in the radiation-induced defect (e.g., VN and VGa) density, the carrier concentrations and mobilities of P-GaN and N−-GaN decrease significantly. Under the proton fluence of 1 × 1015 p/cm2, P-GaN has been transformed into highly resistive N-GaN, resulting in p–i–n diodes losing electrical characteristics of the PN junction. Meanwhile, the P-GaN Ohmic contact has been converted to Schottky contact. In addition, due to a large number of radiation-induced defects in P-GaN and N−-GaN, the reverse leakage current mechanism is revealed to change from space-charge-limited current conduction to Ohmic conduction.

Scalable synthesis of Ta1.1O1.05/biomass carbon composite with multiple structure engineering by boron-doped graphene quantum dot for high-energy supercapacitor

Low intrinsic conductivity and insufficient electroactive sites hinder wide applications of tantalum oxide in supercapacitors. The study reports scalable synthesis of Ta1.1O1.05/biomass carbon (C) composite with multiple structure engineering by boron-doped graphene quantum dot (B-GQD). B-GQD was orderly coordinated with Ta(V) ion to produce Ta-B-GQD complex, sucked into cotton and dried. Followed by annealing at 900 °C in N2 to obtain B-GQD-Ta1.1O1.05/C. Experimental result and theoretical calculation demonstrate that the introduction of B-GQD results in formation of Ta1.1O1.05 nanorods with low valence, small size, highly exposed high-index crystal faces, oxygen vacancies and PN junction. The structure dramatically improves the intrinsic conductivity, electroactive sites and voltage window range. The B-GQD-Ta1.1O1.05/C electrode exhibits high capacitance of 528.3 F g−1 at 0.5 A/g, which is more than that of Ta1.1O1.05 electrode (130.9 F g−1). The flexible symmetrical supercapacitor provides ultrahigh capacitance of 374.1 F g−1 at 1 A/g, high-rate capacity of 207.8 F g−1 at 50 A/g, capacity retention of 98.7 % after 10,000 cycles at 10 A/g and energy density of 113.9 W h Kg−1 at 521.2 W kg−1. The supercapacitor has been successfully applied in the self-powered attitude sensor driven via friction nanogenerator to monitor human walking posture.

Charge Steering in Heterojunction Photocatalysis: General Principles, Design, Construction, and Challenges

Steering charge kinetics is a key to optimizing quantum efficiency. Advancing the design of photocatalysts (ranging from single semiconductor to multicomponent semiconductor junctions) that promise improved photocatalytic performance for converting solar to chemical energy, entails mastery of increasingly more complicated processes. Indeed, charge kinetics become more complex as both charge generation and charge consumption may occur simultaneously on different components, generally with charges being transferred from one component to another. Capturing detailed charge dynamics information in each heterojunction would provide numerous significant benefits for applications and has been needed for a long time. Here, the steering of charge kinetics by modulating charge energy states in the design of semiconductor–metal‐interface‐based heterogeneous photocatalysts is focused. These phenomena can be delineated by separating heterojunctions into classes exhibiting either Schottky/ohmic or plasmonic effects. General principles for the design and construction of heterojunction photocatalysts, including recent advances in the interfacing of semiconductors with graphene, carbon quantum dots, and graphitic carbon nitride are presented. Their limitations and possible future outlook are brought forward to further instruct the field in designing highly efficient photocatalysts.

Carrier transport model of non-carrier-injection light-emitting diode

Non-carrier-injection light-emitting diodes (NCI-LEDs) are expected to be widely used in the next-generation micro-display technologies, including Micro-LEDs and nano-pixel light-emitting displays due to their simple device structures. However, because there is no external charge carrier injection, the internal carrier transport behavior of the NCI-LED cannot be described by using the traditional PN junction and LED theory. Therefore, establishing a carrier-transport model for the NCI-LED is of great significance in understanding its working mechanism and improving device performance. In this work, carrier transport mathematical model of the NCI-LED is established and the mechanical behavior of charge-carrier transport is analyzed quantitatively. Based on the mathematical model, the working mechanism of the NCI-LED is explained, the carrier transport characteristics of the device are obtained. Additionally, the key features, including the length of the induced charge region, the forward biased voltage across the internal PN junction, and the reverse biased voltage across the internal PN junction are studied. Their relationships with the applied frequency of the applied driving voltage are revealed. It is found that both the forward bias and reverse bias of the internal PN junction increase with the driving frequency. When the driving frequency reaches a certain value, the forward bias and the reverse bias of the PN junction will be maintained at a maximum value. Moreover, the length of the induced charge region decreases with the increase of the driving frequency, and when the frequency reaches a certain value, the induced charge region will always be in the state of exhaustion. According to the mathematical model, suggestions for the device optimization design are provided below. 1) Reducing the doping concentration of the induced charge region can effectively increase the voltage drop across the internal LED; 2) employing the tunneling effect occurring in the reverse-biased PN junction can effectively improve the electroluminescence intensity; 3) using the square-wave driving voltage can obtain a larger voltage drop across the internal LED and increase the electroluminescence intensity. This work on the carrier transport model is expected to e present a clear physical figure for understanding the working mechanism of NCI-LED, and to provide a theoretical guidance for optimizing the device structure.

THE ROLE OF ELASTIC STRESS DURING THERMOMIGRATION OF LIQUID ZONES BASED ON ALUMINUM IN SILICON

The method of thermomigration of liquid zones based on aluminum makes it possible to create complex structures of closed channels with boundaries formed from p-n junctions in single-crystal silicon wafers. The channels are characterized by the uniformity of their properties, and the pn junctions are characterized by their sharpness. Such structures are used in high-current electronics, photovoltaics, and microelectromechanical converters. Volumetric deformation inside and outside the channel due to alloying of silicon with aluminum leads to the formation of mechanical stresses. The equilibrium shape of the channels formed at high temperatures is determined by the minimum elastic energy and depends on the material parameters and geometry of the structure. Within the framework of the linear theory of elasticity, the behavior of elastic energy during the formation of the structure of thermomigration channels at high temperatures doped with aluminum in a single-crystalline (001) cut disk was studied. The simulation was performed using the finite element method in the COMSOL Multiphysics mathematical package. The study was carried out for practically important structures in which the direction of the edges is oriented along the diagonal of the square. Only such structures do not have breaks during the process of thermomigration. Based on the calculation results, it was revealed that the minimum elastic energy corresponds to structures with different crystalline orientations inside the channel and outside it – in the main silicon matrix. The direction of the crystalline axes inside the channel, corresponding to the minimum elastic energy, is rotated by 45 degrees in the plane of the disk relative to the direction of the axes of the main matrix of the silicon crystal. In addition, calculations showed that with such a turn, the shape of the channels changes. The minimum elastic energy corresponds not to vertical structures, but to inclined ones. The angle of inclination of the pyramids depends on the width of the channels and the distance between them.

2-D Photo-Thermal Distribution and Structures of Flip-Chip Mini Light-Emitting Diodes by Microscopic Hyperspectral Imaging

Given the growing interest in micro-scale thermal management of mini- and micro-light-emitting diodes (LEDs), it’s crucial to develop an effective two-dimensional (2D) junction temperature measurement method. In this paper, the microscopic hyperspectral imaging (μ-HSI) technique has been proposed to probe the 2D photo-thermal distribution of the flip-chip mini-LEDs. Running on a two-axis rotating platform, μ-HSI is able to directly focus on the epitaxial layer surface (episurface) and lateral side of the LED chips to acquire their 2D spectral distributions. Subsequently, the full width at half maximum matrix was extracted to deduce the 2D junction temperature distributions. As a result, the location and temperature distribution of the active layer, i.e., PN junction, can be determined accurately. The mean temperature of the episurface approximately matches that of the active layer. The Raman shift method was applied to verify the accuracy of the μ-HSI technique. In addition, the extra fine structures as well as temperature distributions of the interface between the episurface and sapphire or electrodes are distinguished and analyzed by this technique. This work offers an effective tool for the quality improvement and thermal management of mini-LEDs.

Gate Tunable Lateral 2D Pn Junctions: An Analytical Study of Its Electrostatics

The electrostatics of two-dimensional (2D) lateral pn homojunctions considering the impact of electrostatic doping by means of two split bottom-gates are studied here. Analytical expressions are obtained from the solution of the 2D Poisson equation considering a depletion approximation. Straightforward analytical models for the electrostatic potential and the depletion width within both the dielectric and the 2D semiconductor are obtained for both the symmetrical and asymmetrical cases. In contrast to the case of devices with chemical doping, the obtained depletion width model of devices with electrostatic doping do not depend on the dielectric constant but only on the electrostatic potential and oxide thickness. The models describe the electrostatics of gate-tunable 2D pn junctions at arbitrary bias. A benchmark against numerical device simulations of MoS2-based pn junctions validate the analytical models.

Switch-Beam Antenna Techniques for Bridge Structural Health Monitoring With GaAs-Based Solar Energy Harvesting

<bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">The structural health monitoring (SHM) of bridges with wireless sensor networks (WSNs) is addressed by leveraging two distinct but interrelated aspects: GaAs-based solar energy harvesting and switched-beam antenna strategies in combination with asynchronous media access control (MAC) protocols. The joint optimization of solar energy harvesting and switched-beam directional antennas at the nodes is considered and compared with an equivalent omnidirectional antenna network. To address the limited energy budget in battery-based sensor nodes which is a serious limitation in long-lived applications such as bridge SHM, an efficient solar harvesting solution is put forth based on the good performance of GaAs cells even under low-light conditions. Given the current state of the art in GaAs cells, single-junction cells were selected due to the cost of double-or triple-junction versions. The simulation model includes the residual energy capacity with GaAs-based solar energy harvesting of actual selected components (microcontroller, radio interface chip). The model was implemented on top of the Omnet<inline-formula> <tex-math notation="LaTeX">$++$</tex-math> </inline-formula> and Silvaco Atlas simulator. The comparative study in this article provides insights into realistic bridge SHM sensor networks, leveraging solar energy harvesting and switched-beam antennas.</b>