Diode-like Behavior Research Articles

UV-A to UV-B electroluminescence of core-shell GaN/AlGaN wire heterostructures

Core-shell GaN/AlGaN multiple quantum wells (MQWs) embedded in a p–n junction are integrated on the upper part of GaN microwires grown by silane-assisted metal organic vapor phase epitaxy. Dispersed wires are then contacted by electron beam induced deposition for fabrication of single wire UV-LED devices. Rectifying diode-like behavior is first demonstrated for both GaN and GaN/AlGaN p-n junctions without a MQW active region. A weak leakage current in the GaN/AlGaN core-shell heterostructure is attributed to an additional conduction path along wire sidewalls. Electroluminescence at 340 nm in UV-A is demonstrated using a GaN (2.6 nm)/Al0.3Ga0.7N (3 nm) heterostructure embedded in a GaN/Al0.3Ga0.7N p–n junction. This value is even decreased to 310 nm by reducing the well thickness to 0.9 nm and increasing the Al-content of barriers (up to 60%) integrated in the GaN/Al0.3Ga0.7N p–n junction. This work demonstrates UV-B emission based on single wire core-shell UV-LEDs.

Asymmetric propagation of acoustic waves in a conical granular chain

An acoustic wave asymmetric propagation is implemented by a conical granular chain here. The chain size is gradually changed interacting via Hertzian contacts. Theoretical modeling and numerical analysis are conducted to investigate the diode-like propagation behavior. Results show that the chain blocks/allows the low-frequency acoustic wave, which depend on different configurations and driving amplitudes in a broad frequency band.

Influence of location junction on ion transfer behavior in conical nanopores with bipolar polyelectrolyte brushes

A bipolar ion diode consists of two positively and negatively charged surfaces that show the distribution of specific ions under different applied voltages. One of the most important electrokinetic phenomena occurring in bipolar nanopores is ionic current rectification (ICR). ICR in nanopores occur when, by applying a voltage to both ends of a nanochannel, the system exhibits non-linear current-voltage behavior or diode-like behavior, in other words, ionic current occurs in a specific direction. In modeling bipolar soft nanochannels, it is usually assumed that the properties of the soft layer and the electrolyte are the same, which is not true for soft layers with high charge densities. In the present work, the effect of sharp and wide aperture radius of nanochannels on ionic current rectification in bipolar nanochannels by coating polyelectrolytic layer with conical geometry in different values of soft layer lengths was studied. For this purpose, by adopting a numerical calculation approach Finite element, Poisson-Nernst-Planck and Navier-Stokes equations were solved for steady-state by considering different permeability values, diffusion coefficient, and dynamic viscosity for polyelectrolyte and electrolyte In general, it can be concluded that the bipolar conical nanopore has a higher ICR than the cylinder geometry with the same average radius If the junction is at the tip of the nanopore. For example, when the mole concentration was equal to c0=50mM, the ICR for the bipolar conical nanopore with a soft layer with an optimal junction at the tip of the nanopore reached 45, while in the bipolar cylindrical nanopore at best (the optimal junction in the middle of the nanopore) reached 25.

Current Transient Spectroscopic Study of Vacancy Complexes in Diamond Schottky p-i-n Diode

The present state-of-the-art of junction-based diamond electronic devices is limited by the challenges inherent to the synthesis of n-type layers, where the dopant itself forms defect complexes that are donor compensating centers. Recently, the fabrication of diamond Schottky p-i-n diodes (SPINDs) by chemical vapor deposition (CVD) of intrinsic diamond films followed by an n-type layer on p-type diamond substrates has been reported to demonstrate excellent diode-like behavior with high rectification factors and surface barrier height at elevated temperatures. However, due to the ultrawide bandgap of diamond and small contact area of the devices, it is challenging to characterize the defect centers that limit the performance of the SPINDs using conventional capacitance transient spectroscopy. In this article, we report the characterization of defect centers in the diamond SPINDs with a contact area of 280 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}\,\,\times \,\,280\,\,\mu \text{m}$ </tex-math></inline-formula> using current transient spectroscopy (CTS), which measures thermally induced emission rates from trap centers through change in device current instead of junction capacitance. The CTS scans in the temperature range 80–800 K revealed the presence of five trap-related peaks. Results from density functional theory (DFT) calculations were used to identify the nature of the traps. While most of the detected traps were identified to be vacancy complexes coupled to phosphorus and hydrogen impurities, one trap has been identified as single carbon vacancy. Most of the phosphorus-related defect complexes were observed to be in neutral and/or negative charge states and were identified as acceptor-like states.

Ferroelectric diode characteristic and tri-state memory in self-assembled BiFeO3 nanoislands with cross-shaped domain structure

Exotic polarization domain configurations in BiFeO3 nanoislands have recently been achieved, promising for exploring next-generation nanoelectronics. Here, different from the earlier reported BiFeO3 nanoislands with a very thin cross-shaped domain wall on LaAlO3 substrates, we observed the cross-shaped domains with a downward polarization separating quad-domains with an upward polarization, which is confirmed by spherical aberration corrected scanning transmission electron microscopy and piezoresponse force microscopy. Interestingly, the cross- and quad-domains show diode-like transport behaviors but with different rectification directions owing to their different polarization orientations. Specifically, an intriguing two-step ferroelectric polarization switching can be realized, which locally results in a tri-state nonvolatile memory. These results broaden the understanding of the interesting polarization configurations in BiFeO3 nanoislands and highlight their potential as high-density information storage.

Investigation of a vertical 2D/3D semiconductor heterostructure based on GaSe and Ga2O3

Mixed-dimensional heterostructures are emerging to be very promising for future electronic and optoelectronic applications. Here, we report on the fabrication and characterization of a 2D/3D vertical van der Waals p–n heterojunction based on p-type gallium selenide (GaSe) and n-type gallium oxide (). Kelvin Probe Force Microscopic (KPFM) measurements have been conducted to estimate the difference in the surface potential values between GaSe and , which is further used to find out the conduction band offset value at the GaSe/ hetero-interface to design the band diagrams. The current–voltage measurements on the device display a diode-like behavior which is attributed to the type-II band alignment, present at the p–n junction interface as per the electron affinities and bandgap values of GaSe and . The device exhibits a high current rectification ratio of ∼2500 extracted at V. The photoresponse properties of the heterostructure are also studied and the figure of merit parameters of the photodetector such as photoresponsivity and specific detectivity have been evaluated for the fabricated device. Since the GaSe/ heterojunction holds a great potential in the field of efficient optoelectronic devices, we believe our study could pave the way to designing innovative optoelectronic devices by integrating low-dimensional materials with conventional 3D semiconducting materials.

Controllable spin diode based on a semiconductor quantum dot

We theoretically propose an all-electrically controlled spin-current diode consisting of a quantum dot sandwiched between one normal electrode and one ferromagnetic electrode. By applying a spin bias V S across one electrode, the spin current distribution shows a rectification effect; that is, in the forward spin bias regime, a spin current can tunnel through the junction, while in the reverse bias regime, the current is tiny. Such asymmetry in the spin-current profile suggests diode-like behaviour with respect to the spin bias. Moreover, the polarity direction of this spin-current diode can be manipulated and reversed by adjusting the gate voltage, which is much more feasible than the approach with traditional charge-current diodes. The present device can be realized by current technologies and has potential applications in spintronics or quantum information processing.

Room temperature magnetic field modulation of diode-like behavior in Ca-doped BiFeO3 thin films

Bi1-xCaxFeO3 (x = 0, 0.1) thin films were synthesized by a sol-gel spin coating method. A diode-like current–voltage characteristic was investigated in a Bi0.9Ca0.1FeO3 (BCFO) thin film. By Ca element doping, the current–voltage characteristic was changed from a traditional symmetric variation to a diode-like behavior. Besides, the modulation effects of a magnetic field on Pt/BCFO/Pt/Ti/SiO2/Si devices have been investigated. Using some micro-analysis methods, such as x-ray photoelectron spectroscopy and transmission electron microscopy, possible mechanisms were discussed on the basis of an oxygen vacancy modulated Schottky-like barrier. The control of the resistance state with the magnetic field means larger degrees of freedom, and this is crucial for further application of BiFeO3-based materials in higher density memory devices.

Characterization of Eu doped ZnO micropods prepared by chemical bath deposition on p-Si substrate

The chemical bath deposition method was used to synthesize Eu-doped ZnO on p-type (100) silicon. The SEM image shows the formation of micropod-like ZnO. EDX and XPS measurements showed an increase in the Eu concentration up to 2.54% and the simultaneous presence of Eu3+ and Eu2+. XRD analysis confirmed that the interstitial Eu3+ ions distorted the four tetrahedral bonds, and the substitution of Eu2+ ions increased the c lattice parameter. Only Eu3+5D0→7F2 transition-related emission was observed, so a weak transfer energy from the ZnO matrix to the Eu ion occurred. However, the competition between the emission of deep-level defects in the host matrix and that of Eu3+ ions deforms the visible emission towards the red color. The I–V measurements of the Eu-ZnO/p-Si heterojunctions showed diode-like behavior with a low rectification ratio and a barrier height around 0.84 eV not affected by the Eu concentration.

Investigations on Asymmetric Transmittivity of Optical Devices and Different Diode-Like Behaviors

Investigations on Asymmetric Transmittivity of Optical Devices and Different Diode-Like Behaviors

Second Harmonic Generation Exploiting Ultra-Stable Resistive Switching Devices for Secure Hardware Systems

In the era of Big Data and Internet of Things (IoT), information security has emerged as an essential system and application metric. The information exchange among the ubiquitously connected smart electronic devices requires functioning reliably in harsh environments, which highlights the need for securing the hardware root of trust. In this work, by leveraging the uniform nonlinear resistive switching of emerging electroforming-free analog memristive device based on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {BiFeO}_3$</tex-math></inline-formula> (BFO) thin film, the security-oriented hardware primitive (SoHP) system is developed and optimized with high-security level. The SoHP system utilizes the distinguishable power conversion efficiency generated at second and higher harmonics in low resistance state (memristor with diodelike behavior) and high resistance state (memristor with high resistive behavior) of memristive devices. By exploring the significant influence of writing bias and operational frequency in sourcing input voltage on the dynamic switching behavior of memristive device, the novel 2-memristor encoding scheme and 1-memristor decoding scheme are developed for SoHP system, which realizes a frequency enhancement of 4000 times in comparison to 1-memristor encoding scheme and 2-memristor decoding scheme. The encoded data bits that generated from physically implemented SoHP system pass diverse statistical test suites (i.e. ENT, BSI, and NIST SP-800.22 statistical test suites), which indicates the high randomness distribution of the encoded data and the high-security level of the proposed memristive encoding system.

Tunable Symmetry-Breaking-Induced Dual Functions in Stable and Photoswitched Single-Molecule Junctions.

The aim of molecular electronics is to miniaturize active electronic devices and ultimately construct single-molecule nanocircuits using molecules with diverse structures featuring various functions, which is extremely challenging. Here, we realize a gate-controlled rectifying function (the on/off ratio reaches ∼60) and a high-performance field effect (maximum on/off ratio >100) simultaneously in an initially symmetric single-molecule photoswitch comprising a dinuclear ruthenium-diarylethene (Ru-DAE) complex sandwiched covalently between graphene electrodes. Both experimental and theoretical results consistently demonstrate that the initially degenerated frontier molecular orbitals localized at each Ru fragment in the open-ring Ru-DAE molecule can be tuned separately and shift asymmetrically under gate electric fields. This symmetric orbital shifting (AOS) lifts the degeneracy and breaks the molecular symmetry, which is not only essential to achieve a diode-like behavior with tunable rectification ratio and controlled polarity, but also enhances the field-effect on/off ratio at the rectification direction. In addition, this gate-controlled symmetry-breaking effect can be switched on/off by isomerizing the DAE unit between its open-ring and closed-ring forms with light stimulus. This new scheme offers a general and efficient strategy to build high-performance multifunctional molecular nanocircuits.

Effects of boron oxide addition on electrical properties of yttrium-doped bismuth-based zinc oxide varistors

The optimal amount of B2O3 (0.75 mol%) drastically improved the electrical properties of Y-doped varistors, reducing the leakage current to 0.8 μA/cm2 while maintaining exceptionally long-term stability against DC electrical degradation and a varistor voltage around 900 V/mm. Boron ions were found with Bi ions in Y-compounds, which contributed to formation of a Bi-rich glass phase containing B at grain boundaries when the B2O3 content was above 0.75 mol%. The change in microstructure affected the donor density and barrier structure, leading to a change in electrical properties. The Bi-rich phase first reduced the Co concentration in the ZnO grains, thereby decreasing the donor density ND. When large amount of B2O3 was added, some Co remained in ZnO grains, causing an increase in ND. A new analytical method using the differential resistance RD for the nonlinear voltage–current density relation was proposed to clarify the effects of B2O3 addition. This method separates the three differential resistance RDi values (i = 1, 2, 3) and was used to analyze the corresponding conduction process in forward-biased region I, reverse-biased region III, and interface region II of the energy band. The RD1 and RD2 values exhibited junction diode-like behavior in regions I and III. The value of RD2 that correlated with αasMAX and the long-term stability of the varistor and RD3 may be related to region II.

Fluidic bacterial diodes rectify magnetotactic cell motility in porous environments

Directed motility enables swimming microbes to navigate their environment for resources via chemo-, photo-, and magneto-taxis. However, directed motility competes with fluid flow in porous microbial habitats, affecting biofilm formation and disease transmission. Despite this broad importance, a microscopic understanding of how directed motility impacts the transport of microswimmers in flows through constricted pores remains unknown. Through microfluidic experiments, we show that individual magnetotactic bacteria directed upstream through pores display three distinct regimes, whereby cells swim upstream, become trapped within a pore, or are advected downstream. These transport regimes are reminiscent of the electrical conductivity of a diode and are accurately predicted by a comprehensive Langevin model. The diode-like behavior persists at the pore scale in geometries of higher dimension, where disorder impacts conductivity at the sample scale by extending the trapping regime over a broader range of flow speeds. This work has implications for our understanding of the survival strategies of magnetotactic bacteria in sediments and for developing their use in drug delivery applications in vascular networks.

Enhanced Spin Accumulation in Semiconductor at Room Temperature Using Ni0.65Zn0.35Fe2O4(NZFO) as Spin Injector in NZFO/MgO/p-Si Device

In this article, the fabrication of a Ni0.65Zn0.35Fe2O4/MgO/p-Si heterostructure device has been optimized using the pulsed laser deposition (PLD) technique, and a detailed investigation of its structural, electrical, and magnetic features has been performed experimentally. The electronic and magneto-transport characteristics have been explored in the temperature range of 100–300 K. The current-voltage (I-V) characteristics of the heterojunction have been recorded, which displayed an excellent rectifying magnetic tunnel diode-like behavior throughout that temperature regime. The application of an external magnetic field parallel to the plane of the NZFO film causes the current (I) across the junction to decrease, clearly indicating positive junction magnetoresistance (JMR) of the heterostructure. The root of displaying positive magnetoresistance in our heterojunction has been well justified using the standard spin injection model. The electrical injection of spin-polarized carriers and its accumulation and detection in a p-Si channel have been demonstrated using the NZFO/MgO tunnel contact using a three-terminal (3-T) Hanle device. The parameters such as spin lifetime (99 ps), spin diffusion length (276 nm), and spin polarization (0.44) have been estimated from the Hanle curve detected in our heterostructure at room temperature, making the Ni0.65Zn0.35Fe2O4/MgO/p-Si device a very favorable promising junction structure in the field of spintronics for several device appliances in the future.

Detection of nitrogen atoms as dopants in a zinc oxide crystal lattice incorporated by the effect of a cooling method in a thin film bilayer scheme

The zinc oxide semiconductor can be directed towards p-type or n-type electrical performance depending on the synthesis conditions and fabrication methods, ranging from chemical, sol gel to physical vapor deposition procedures, or the one used in this work: reactive sputtering. Usually this binary oxide, in thin film form, synthesizes into an n-type semiconductor if is fabricated by means of the reactive sputtering method, using an oxygen-poor atmosphere and specific deposition conditions, already established above. However, due to an accident in the synthesis, it was possible to determine the effect that the typical atmosphere at normal atmospheric pressure with 78% nitrogen had on the expected zinc oxide lattice if was abruptly integrated over the scheme. The verification was done using a scratch angle X-ray diffraction characterization, which evidences the incorporation of nitrogen atoms into the zinc oxide crystal by the widening of the lattice parameters. The experimental arrangement analyzed was a bilayer scheme with a first film of n-type zinc oxide and, on this, a second film of the same oxide but p-type. It was possible to conclude that, apart from the desired diode-like behavior of the bilayer, evidenced by the assembly of the half-wave rectifier, there was also evidence of the incorporation of nitrogen in the crystal lattice in the second layer by the notorious shift of the diffraction peak (101).

Ultralong π-Conjugated Bis(terpyridine)metal Polymer Wires Covalently Bound to a Carbon Electrode: Fast Redox Conduction and Redox Diode Characteristics.

We developed an efficient and convenient electrochemical method to synthesize π-conjugated redox metal-complex linear polymer wires composed of azobenzene-bridged bis(terpyridine)metal (2-M, M = Fe, Ru) units covalently immobilized on glassy carbon (GC). Polymerization proceeds by electrochemical oxidation of bis(4′-(4-anilino)-2,2′:6′,2″-terpyridine)metal (1-M) in a water–acetonitrile–HClO4 solution, affording ultralong wires up to 7400 mers (corresponding to ca. 15 μm). Both 2-Fe and 2-Ru undergo reversible redox reactions, and their redox behaviors indicate remarkably fast redox conduction. Anisotropic hetero-metal-complex polymer wires with Fe and Ru centers are constructed via stepwise electropolymerization. The cyclic voltammograms of two hetero-metal-complex polymer wires, GC/[2-Fe]–[2-Ru] (3) and GC/[2-Ru]–[2-Fe] (4), show irreversible redox reactions with opposite electron transfer characteristics, indicating redox diodelike behavior. In short, the present electrochemical method is useful to synthesize polymer wire arrays and to integrate functional molecules on carbon.

Inverted Ion Current Rectification-Based Chemical Delivery Probes for Stimulation of Neurons.

Ion current rectification (ICR), diodelike behavior in surface-charged nanopores, shows promise in the design of delivery probes for manipulation of neural networks as it can solve diffusive leakages that might be critical in clinical and research applications. However, it has not been achieved because ICR has restrictions in nanosized dimension and low electrolyte concentration, and rectification direction is inappropriate for delivery. Herein, we present a polyelectrolyte gel-filled (PGF) micropipette harnessing inverted ICR as a delivery probe, which quantitatively transports glutamate to stimulate primary cultured neurons with high efficiency while minimizing leakages. Since the gel works as an ensemble of numerous surface-charged nanopores, the current is rectified in the micro-opening and physiological environment. By extending the charge-selective region using the gel, inverted ICR is generated, which drives outward deliveries of major charge carriers. This study will help in exploring new aspects of ICR and broaden its applications for advanced chemical delivery.

Pure spin-current diode based on interacting quantum dot tunneling junction* *Project supported by the National Natural Science Foundation of China (Grant No. 11404322) and the Natural Science Foundation of Huai’an (Grant No. HAB202150).

A magnetic field-controlled spin-current diode is theoretically proposed, which consists of a junction with an interacting quantum dot sandwiched between a pair of nonmagnetic electrodes. By applying a spin bias V S across the junction, a pure spin current can be obtained in a certain gate voltage regime,regardless of whether the Coulomb repulsion energy exists. More interestingly, if we applied an external magnetic field on the quantum dot, we observed a clear asymmetry in the spectrum of spin current I S as a function of spin bias, while the charge current always decays to zero in the Coulomb blockade regime. Such asymmetry in the current profile suggests a spin diode-like behavior with respect to the spin bias, while the net charge through the device is almost zero. Different from the traditional charge current diode, this design can change the polarity direction and rectifying ability by adjusting the external magnetic field, which is very convenient. This device scheme can be compatible with current technologies and has potential applications in spintronics or quantum processing.

Upconversion of Bi4Ti3O12:Er and its evaluation in silicon solar cell yield

Using the sol–gel method, Er3+-doped Bi4Ti3O12 films were prepared on monocrystalline silicon substrates. The current–voltage characteristics for the prepared structures were measured using a 300 W solar simulator at air mass 1.5 (AM1.5) and at a frequency of 50–60 Hz. In general, all samples maintained a clearly visible diode-like behavior. It was observed that the reference cell had a lower energy conversion efficiency compared to the silicon solar cell modified with the BIT:Er films adhered to its back contact in all cases under AM1.5 illumination. The 2 mol% sample reached an open circuit voltage of 544 mV and a short circuit current of 39.8 mA/cm2 with a 2.2% excess over the reference solar cell efficiency.