Rectification Characteristics Research Articles

Current Rectification, Resistive Switching, and Stable NDR Effect in BaTiO3/CeO2 Heterostructure Devices

AbstractElectronic devices with simultaneous manifestation of multiphysical properties are of great interest due to their possible application in multifunctional devices. In the present study, simultaneous execution of negative differential resistance (NDR) effect, current rectification (≈105), and resistive switching characteristics (≈103) are demonstrated in BaTiO3/CeO2 heterostructure. Although the negative differential effect has gained huge attention, its instability and poor reproducibility at room temperature are the main obstacles to its possible application in electronic devices. However, in this report, the NDR is observed even after hundreds of cycles in BaTiO3/CeO2 heterostructure at 300 K. For a detailed analysis of the NDR effect, AC conductance spectroscopy is performed, which reveals that the presence of NDR is associated with trapping/detrapping of charge carriers at interface states formed at the BaTiO3/CeO2 interface. In addition, the resistive switching and rectification effect are demonstrated due to a barrier at the BaTiO3/CeO2 interface, which can be strongly modulated by thickness (20, 50, and 80 nm) based ferroelectric polarization of BaTiO3. However, the results show that the remarkable performance of these devices makes them a potential candidate for application in multifunctional devices.

Research on Pt/NiOx/WO3-x:Ti/W Multijunction Memristors with Synaptic Learning and Memory Functions.

Artificial synapses based on biological synapses represent a new idea in the field of artificial intelligence with future applications. Current two-terminal RRAM devices have developed tremendously due to the adjustable synaptic plasticity of artificial synapses. However, these devices still have some problems, such as current leakage and poor durability. Here, we demonstrate a Pt/NiOx/WO3-x:Ti/W memristor with a pn-type heterojunction and two metal-semiconductor contacts, which exhibits good rectification. Due to the change in the internal potential barrier, the devices possess multiconductance states under different pulse modulations and memory characteristics, similar to synapses. The rectification characteristics of the device exhibit stable enhancement and suppression behavior. Each device in the 10 × 10 cross array we constructed can be written correctly, which verifies that leakage current does not appear in the device. The structure proposed in this work has great significance for the integration of large-scale memristor cross arrays.

Effect of Plasma Treatment on Metal Oxide p–n Thin Film Diodes Fabricated at Room Temperature

AbstractThere is a need for a good quality thin film diode using a metal oxide p–n heterojunction as it is an essential component for the realization of flexible large‐area electronics. However, metal oxide‐based diodes normally show poor rectification characteristics whose origin is still poorly understood; this is holding back their use in various applications. A systematic study of the origins of the poor performance is performed based on bias‐stress measurements using a cuprous oxide (Cu2O)/amorphous zinc‐tin oxide (a‐ZTO) heterojunction as an example. This suggests that multiple carrier trapping and thermal release of carriers in defect states stemming from oxygen vacancies at the heterojunction interface is the primary cause of poor rectification. It is demonstrated that a plasma treatment is an effective way to optimize the population of oxygen vacancies at the heterojunction interface based on extensive material analyses, allowing a significant improvement in the diode performance with a much‐enhanced rectification ratio from ≈20 to 10 000, and a consequent facilitation of the next‐generation of ubiquitous electronics.

Fabrication of a poly(N-vinyl carbazole)/ϵ-Ga2O3 organic–inorganic heterojunction diode for solar-blind sensing applications

Herein, a poly(N-vinyl carbazole) (PVK)/ϵ-gallium oxide (ϵ-Ga2O3) heterojunction device was fabricated by spin coating prepared PVK solution onto a ϵ-Ga2O3 thin film produced by metal-organic chemical vapor deposition. Under 254 nm ultraviolet light, the device shows obvious rectification characteristics of 37 at ±2 V and has a response speed of 0.52 s rise time and 0.11 s decay time at 5 V. Current–voltage measurement confirmed that the prepared device has the potential to become a self-powered photodetector and displays good stability and a fast response speed under various light intensities and different voltages.

Volatile and Nonvolatile Memory Operations Implemented in a Pt/HfO₂/Ti Memristor

Both nonvolatile and volatile characteristics are realized in the same Pt/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ti memristor by specific electrical operations. The resistance states of nonvolatile memory hardly change for over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> s, whereas the low resistance state of volatile memory is unstable, and degenerates gradually into the high resistance state in hundreds of seconds. The volatile device was forming-free and realized only in clockwise voltage sweeping. Compared to the nonvolatile device, the operating current of volatile device was lower and showed obviously rectification characteristics. Emulations of synaptic plasticity including short-term plasticity, long-term plasticity, and spike-time-dependent-plasticity were achieved. Finally, the resistive switching mechanism of the volatile device was analyzed and assumed to be the trapping and detrapping of electrons by traps near the interface of Pt/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> .

Characterization of 2D boron nitride nanosheets with hysteresis effect in the Schottky junctions

Carbon doped two-dimensional (2D) hexagonal boron nitride nanosheets (BNNSs) are obtained through a CO2—pulsed laser deposition (CO2—PLD) technique on silicon dioxide (SiO2) or molybdenum (Mo) substrates, showing - stable hysteresis characteristics over a wide range of temperatures, which makes them a promising candidate for materials based on non-volatile memory devices. This innovative material with electronic properties of n-type characterized in the form of back-to-back Schottky diodes appears to have special features that can enhance the device performance and data retention due to its functional properties, thermal-mechanical stability, and its relation with resistive switching phenomena. It can also be used to eliminate sneak current in resistive random-access memory devices in a crossbar array. In this sense constitutes a good alternative to design two series of resistance-switching Schottky barrier models in the gold/BNNS/gold and gold/BNNS/molybdenum structures; thus, symmetrical and non-symmetrical characteristics are shown at low and high bias voltages as indicated by the electrical current-voltage (I–V) curves. On the one hand, the charge recombination caused by thermionic emission does not significantly change the rectification characteristics of the diode, only its hysteresis properties change due to the increase in external voltage in the Schottky junctions. The addition of carbon to BNNSs creates boron vacancies that exhibit partially ionic character, which also helps to enhance its electrical properties at the metal-BNNS-metal interface.

Towards significant enhancement of structural and optoelectronic properties of porphyrin palladium(II) complex: A theoretical and experimental analysis

In the present investigation, the nanostructure of porphyrin palladium(II) complex thin films was fabricated by low-cost conventional thermal analysis. The experimental and simulation investigations were used for the analysis of the structure and the unique optical characteristics for optoelectronic applications. The simulation processes using TD-DFT/ B3LYP were implemented to extract the distinguished geometry optimizations and other related parameters. The quantum theory of atoms in molecules (QTAIM) was additionally applied for the studied complexes to evaluate their peculiar electronic features. An indexation of XRD was performed to give a full identification of the crystal structure and supported by the results of transmission electron microscopy images. The investigation of the surface morphology and its quality for the optical applications was established using the atomic force microscopy, AFM supported surface topography mapping images. The optical properties confirm two main direct transitions with determined band gaps of 2.31 and 2.98 eV. The experimental optical gap was comparable with those theoretically extracted using DFT. The characteristics of the current density-voltage measurements verified rectification in the dark and under different values of illuminations. The device showed remarkable rectification characteristics with good responsitivity under illumination conditions. The maximum external quantum efficiency of 9.8% was obtained and compared to other organic-based devices.

N–SrTiO3/p-GaN heterojunctions: A white light-emitting diode with a broad luminescence spectrum

We report a white light-emitting diode (LED) based on the n-SrTiO3 (n-STO)/p-GaN heterojunction. The n-STO/p-GaN heterojunction LED shows the good rectification characteristics in the current−voltage measurements and an intense white light emission with a broad luminescence spectrum in electroluminescence (EL) measurements. There are two strong and broad emission bands at the regions from blue to red (450–650 nm, center located at ~525 nm) and from ultraviolet to blue (350–450 nm, center located at ~410 nm), which are respectively derived from the p-type GaN and n-type STO layers. The photoluminescence (PL) spectra indicate that the n-STO film has an emission band from ultraviolet (UV) to blue which is associated with the near band-edge emission and defect-related radiative recombination, and the p-GaN layer has an emission band from blue to red. Our results suggest that n-STO/p-GaN heterojunction is an alternate and effective heterostructure to achieve LEDs with high intense white light emission.

NiO/GaN p-n junction ultraviolet photodetector and self-powered technology

&lt;sec&gt; Ultraviolet photodetector plays an important role in fire warning, missile tracking and dose detecting of ultraviolet sterilization and disinfection, which is closely related to human lives. With the development of integrated detection system, the requirements for the size and energy consumption of the detector are becoming more and more stringent. Traditional detector that requires an external power supply can no longer meet these requirements. Moreover, a traditional ultraviolet detector is mainly composed of first-generation semiconductors and second-generation semiconductors. These semiconductors have small band gaps and large cut-off wavelengths, and are more suitable for infrared detection. When used for implementing the ultraviolet detection, an additional layer is often required, which increases not only the volume but also the cost. &lt;/sec&gt;&lt;sec&gt; Gallium nitride (GaN), as a third-generation semiconductor, has a band gap of 3.4 eV and a corresponding absorption edge of 365 nm. It is a natural ultraviolet detection material. At the same time, the excellent physical and chemical properties make the devices prepared by GaN have high stability. In recent years, some studies have shown that the GaN-based ultraviolet photodetectors have excellent responsiveness, but each of these detectors usually requires an external bias and has a slow response speed. Here, we propose a high responsivity, fast response speed and self-powered ultraviolet photodetector based on NiO/GaN p-n junction. By using the magnetron sputtering, a layer of 70 nm thick p-NiO film is deposited on a high-quality n-GaN film that has been grown on a sapphire substrate by the metal-organic chemical vapor deposition. The fabricated p-n junction shows obvious rectification characteristics at ± 0.5 V. Due to the existence of the built-in electric field, the device can work without externally applied bias. Under zero bias, the detector shows a responsivity of 272.3 mA/W for 365 nm ultraviolet light while the intensity is 50 μW/cm&lt;sup&gt;2&lt;/sup&gt;, and has a detectivity as high as 2.83 × 10&lt;sup&gt;14&lt;/sup&gt; Jones. This indicates that the detector has a high sensitivity even for very weak light. Owing to the good crystallinity of the film, the dark current is as low as 10&lt;sup&gt;–10&lt;/sup&gt; A, the switching ratio is &gt; 10&lt;sup&gt;3&lt;/sup&gt;, and the response speed reaches 31 ms. These excellent properties show the broad application prospects of the devices based on NiO/GaN p-n junctions in the field of self-powered ultraviolet detection, and thus providing new ideas for the future development of intelligent integration. &lt;/sec&gt;

Improved rectification characteristics by engineering energy barrier height in TiOx-based RRAM

Resistive random access memory (RRAM) is a strong candidate for next-generation memory. Despite its versatility, the sneak path current severely threatens accurate read operations, preventing RRAM from being expanded to high density array. To solve this sneak path current, here we propose a method to enhance a rectification effect through barrier height engineering. We fabricated two TiOx-based devices, Al/TiOx/Al devices as a control group and Cu/TiOx/Al devices as an experimental group, and compare their rectification characteristics. As a result, a rectification ratio in Cu/TiOx/Al devices is much larger than that of Al/TiOx/Al devices, e.g., approximately 122 times for low-resistance-state and 251 times for high-resistance-state. Furthermore, we analyze the energy band diagram considering the bias polarity and electric-field-driven oxygen ion migration. It is confirmed that the rectification effect results from high energy barrier height between Cu top electrode and TiOx. In addition, it is established that the high rectification ratio of Cu/TiOx/Al devices is capable of constructing large-sized memory array with reliable read margin by simply adjusting energy barrier height

Morphology Controlled Synthesis of Composition Related Plasmonic CuCdS Alloy Nanocrystals.

Cu-based ternary alloy nanocrystals have emerged for extensive applications in solar cells, light-emitting devices (LEDs), and photoelectric detectors because of their low-toxicity, tunable band gaps, and large absorption coefficients. It is still an enormous challenge that regulating optical and electrical properties through changing their compositions and shapes in alloy nanocrystals. Herein, we present a facile method to synthesize CuCdS alloy nanocrystals (NCs) with tunable compositions and shapes at relatively low temperature. Different morphologies of monodisperse CuCdS nanocrystals are tailored successfully by simply adjusting the reaction temperature and Cu:Cd precursor molar ratio. The as-synthesized nanocrystals are of homogeneous alloy structures with uniform obvious lattice fringes throughout the whole particles rather than heterojunction structures. The localized surface plasmon resonance (LSPR) absorption peaks of CuCdS NCs are clearly observed and can be precisely tuned by varying the Cu:Cd molar ratio. Moreover, current–voltage (I–V) behaviors of different shaped CuCdS nanocrystals show certain rectification characteristics. The alloy CuCdS NCs with tunable shape, band gap, and compositionpossess a potential application in optoelectronic devices.

Rectifying Characteristics of the Perovskite Oxide La1−xSrxMnO3/Nb‐0.7 wt%‐Doped SrTiO3 Heterojunction

The influence of Sr‐doping on the rectifying characteristics of the perovskite oxide La1−xSrxMnO3/Nb‐0.7 wt%‐doped SrTiO3(LSMO/NSTO) heterojunction is studied systematically. Clear rectification characteristics are observed in the Au/LSMO/NSTO heterojunction with Sr‐doping rate of 0.1–0.6 at 300 K. The threshold voltage and Schottky barrier height increase linearly with the increase in Sr‐doping. Combined with first‐principles calculations, it is found that the variation of Sr‐doping concentration directly leads to a change in the LSMO work function, then a change in barrier height, and finally a change in the threshold voltage and rectification characteristics. Ultimately, it is proved that the rectification characteristics of the perovskite metal oxide heterostructure are consistent with the potential barrier mechanism of semiconductors. The rectifying characteristics of the perovskite oxide p–n junction can be well modulated by the change in energy band structure caused by Sr‐doping. These results lay a foundation for further understanding of the rectification characteristics of the perovskite oxide heterostructure and improving its application value.

Investigation of the Resistive Switching Mechanisms and Rectification Characteristics of HfO₂-Based Resistive Random Access Memory Devices with Different Electrode Materials.

To study the substitutability of noble metal electrodes in memristors, the effect of Pt/HfO₂/Ti structure on the replacement of noble metal electrode Pt by different electrodes was studied. Compared with the unsubstituted devices, the HfO₂-based RRAM devices with TiN and TiOxNy electrodes devices showed good resistive switching performance and resistive switching mechanism under oxygen ion migration. Five devices were prepared, and their resistive switching mechanism under oxygen ion migration was investigated. Moreover, besides the resistive switching phenomenon of these RRAM devices, it was found that significant rectifying characteristics were exhibited in a highresistance state (HRS). This phenomenon can be explained by regulation of the Schottky barrier of the interface between the top electrode and the resistive layer, which can be influenced by the migration of oxygen vacancies.

Pd decorated TiO2 nanotube array Schottky barrier diodes for efficient hydrogen sensing application

Well aligned TiO2 nanotube arrays have been synthesized via electrochemical anodization, and Pd-based nanoparticles (NPs) were decorated by electrodeposition with the aid of UV irradiation. A new back-to-back Schottky barrier diode (SBD) was formed by connecting with Ag–(Pd decorated TiO2)–Ti. We found that such an SBD sensor has excellent hydrogen (H2) sensing performances at a working temperature of 80 °C, with a detection limit as low as 1 ppm as well as a quick response time within 10 s at a low bias voltage (0.025 V). I–V curves and electrochemical impedance spectroscopy analysis demonstrate a typical rectification characteristic of SBD as well as a dramatic decrease of the barrier height of SBD during the H2 sensing process. The high H2 sensing performance of a Pd-based NP decorated TiO2 nanotube array film SBD could be attributed to the synergism of the highly ordered nano-porous configurations and the Pd-based NP (with a high catalytic active metallic Pd nanoshell layer) decoration providing the enhancement of H2 spillover effect (and/or electronic sensitization) related redox processes.

Ionic Current Rectification of Porous Anodic Aluminum Oxide (AAO) with a Barrier Oxide Layer.

Synthetic nanofluidic diodes with highly nonlinear current-voltage characteristics are currently of particular interest because of their potential applications in biosensing, separation, energy harvesting, and nanofluidic electronics. We report the ionic current rectification (ICR) characteristics of a porous anodic aluminum oxide membrane, whose one end of the nanochannels is closed by a barrier oxide layer. The membrane exhibits intriguing pH-dependent ion transport characteristics, which cannot be explained by the conventional surface charge governed ionic transport mechanism. We reveal experimentally and theoretically that the space charge density gradient present across the 40-nm-thick barrier oxide is mainly responsible for the evolution of ICR. Based on our findings, we demonstrate the formation of a single 5-8-nm-sized pore in each hexagonal cell of the barrier oxide. The present work would provide valuable information for the design and fabrication of future ultrathin nanofluidic devices without being limited by the engineering of the nanochannel geometry or surface charge.

Diode-like rectification characteristics of BiFeO3-based /Zn1-xNixFe2O4 bilayered films for application of ferroelectric field effect transistors

The microscopic strain caused by lattice mismatch show great differences in the Bi0.89Ho0.08Sr0.03Fe0.95Mn0.03Zn0.02O3/Zn1-xNixFe2O4 (BHSFMZO/ZNxFO) bilayered films prepared by chemical solution deposition, which affects the state between the interfaces. The p-n heterojunction is formed between the BHSFMZO and ZNxFO layers of the BHSFMZO/ZNxFO (x ≤ 0.3) bilayered films. And its leakage current shows obvious diode-like rectifying I–E characteristic and the ferroelectric properties show hysteresis. BHSFMZO/ZNxFO (x ≤ 0.3) bilayered films prepared by chemical solution deposition may be helpful to suppress the charge injection from semiconductor to ferroelectric thin film in ferroelectric field effect transistor and may have potential applications in self-rectified resistive random access memory due to their excellent resistance switching behaviors.

Functionalized Nanogap for DNA Read-Out: Nucleotide Rotation and Current-Voltage Curves.

Functionalized nanogaps embedded in nanopores show a strong potential for enhancing the detection of biomolecules, their length, type, and sequence. This detection is strongly dependent on the features of the target biomolecules, as well as the characteristics of the sensing device. In this work, through quantum‐mechanical calculations, we elaborate on representative such aspects for the specific case of DNA detection and read‐out. These aspects include the influence of single DNA nucleotide rotation within the nanogap and the current‐voltage (I‐V) characteristics of the nanogap. The results unveil a distinct variation in the electronic current across the functionalized device for the four natural DNA nucleotides with the applied voltage. These also underline the asymmetric response of the rotating nucleotides on this applied voltage and the respective variation in the rectification ratio of the device. The electronic tunneling current across the nanogap can be further enhanced through the proper choice of an applied bias voltage. We were able to correlate the enhancement of this current to the nucleotide rotation dynamics and a shift of the electronic transmission peaks towards the Fermi level. This nucleotide specific shift further reveals the sensitivity of the device in reading‐out the identity of the DNA nucleotides for all different configurations in the nanogap. We underline the important information that can be obtained from both the I‐V curves and the rectification characteristics of the nanogap device in view of accurately reading‐out the DNA information. We show that tuning the applied bias can enhance this detection and discuss the implications in view of novel functionalized nanopore sequencers.

A self-powered ultraviolet photodiode using an amorphous InGaZnO/p-silicon nanowire heterojunction

This study proposes a novel photodetector (PD) that uses an amorphous InGaZnO (IGZO)/silicon nanowires (SiNWs) heterojunction, in which the IGZO functions as an ultraviolet (UV) light absorption layer and the nanowires provide carrier conduction paths and light trapping centers. The p-n heterojunction shows excellent rectification characteristics in the dark and distinctive photovoltaic behavior under UV illumination. A high responsivity of 0.53 A/W at 380 nm and a quick response time of less than 0.2 ms are achieved. The device exhibits self-powering characteristics under UV illumination due to the amorphous phase of IGZO. The architecture, which combines a wide-bandgap a-IGZO (~3.5 eV) with a narrow-bandgap SiNWs, means that the photo-detection spectra extend from UV to near-infrared. This study demonstrates that the a-IGZO/SiNWs PD is suitable for applications that require high response speeds, broadband detection and self-sufficient functionality.

Large-area vertically stacked MoTe2/β-Ga2O3 p-n heterojunction realized by PVP/PVA assisted transfer

Beta phase gallium oxide (β-Ga2O3) has attracted wide attention due to its unique material property; however, the lack of p-type doping hinders its practical application. Here, we report a 2H-MoTe2/β-Ga2O3 (2-01) vertical p-n heterojunction diode via chemical vapor deposition, which exhibited excellent rectification characteristics with a rectifying ratio of 105, and an on-current density of up to 1 mA/cm2. The depletion comes from strain-free interface of the 2H-MoTe2 and β-Ga2O3 (2-01) by van der Waals force. The band offsets and the interface element distribution of the heterojunction were investigated by the X-ray photoelectron spectroscopy and transmission electron microscope. The valence and conduction band offsets between the 2H-MoTe2 and β-Ga2O3 were consequently determined to be 0.16 eV and 3.56 eV, with a nested gap (type I) band alignment. Moreover, an abnormal build-in potential was observed in the 2H-MoTe2/β-Ga2O3 p-n heterojunction diode which could be attributed to the formation of an interfacial layer of MoOX. These observations in the 2H-MoTe2/β-Ga2O3 heterojunction show the great potential in optoelectronic devices.

Negative Differential Resistance of n-ZnO Nanorods/p-degenerated Diamond Heterojunction at High Temperatures.

In the present study, an n-ZnO nanorods (NRs)/p-degenerated diamond tunneling diode was investigated with regards to its temperature-dependent negative differential resistance (NDR) properties and carrier tunneling injection behaviors. The fabricated heterojunction demonstrated NDR phenomena at 20 and 80°C. However, these effects disappeared followed by the occurrence of rectification characteristics at 120°C. At higher temperatures, the forward current was increased, and the turn-on voltage and peak-to-valley current ratio (PVCR) were reduced. In addition, the underlying mechanisms of carrier tunneling conduction at different temperature and bias voltages were analyzed through schematic energy band diagrams and semiconductor theoretical models. High-temperature NDR properties of the n-ZnO NRs/p-degenerated diamond heterojunction can extend the applications of resistive switching and resonant tunneling diodes, especially in high-temperature, and high-power environments.