High Rectification Ratio Research Articles

Engineering a Smart Nanofluidic Sensor for High-Performance Peroxynitrite Sensing through a Spirocyclic Ring Open/Close Reaction Strategy.

Peroxynitrite (ONOO-) is an important reactive oxygen/nitrogen species that participates in a range of physiological and pathological processes by modulating ion flux through biological channels. Inspired by a ONOO--regulated K+ channel in vivo, herein, we describe the construction of a smart ONOO--driven nanosensor using a spirocyclic ring open/close reaction approach. The prepared nanosensor possessed a prominent ONOO- selectivity and sensitivity and rapid response (∼90 s) owing to the specific reaction between ONOO- and ligands on the nanosensor surface with a high ion rectification ratio (∼10) and ion gating ratio (∼4). Moreover, this nanosensor system also exhibits excellent stability and recyclability. Thus, these results will provide a new direction for the design of nanochannel-based sensors for future practical and biological applications.

Precise Turn-On Voltage Control of MIOSM Thin-Film Diodes with Amorphous Indium-Gallium-Zinc Oxide.

Recently, metal-insulator-oxide semiconductor-metal (MIOSM) thin-film diodes (TFDs) have received attention as next-generation diodes due to their high rectification ratio and broad option on the operating voltage range. Nevertheless, precise turn-on voltage control of the MIOSM TFDs has been required for circuit design convenience. Here, we present a simple and accurate method of controlling the turn-on voltage of MIOSM TFDs. Studies on current-voltage characteristics reveal that controlling carrier injection into trap states in an insulator by oxygen vacancy variation of the oxide semiconductor plays a key role in the turn-on voltage shift of MIOSM TFDs. Moreover, by controlling the trap states in the insulator, the finely tuned turn-on voltages of the MIOSM TFDs are demonstrated for both low-voltage- and high-voltage-driving diodes. MIOSM TFDs with adjustable turn-on voltage, which can be built more efficiently and accurately, are expected to make oxide-based circuit designs more precise and straightforward.

First-Principles Investigation of Pd-Doped Armchair Graphene Nanoribbons as a Potential Rectifier

A first-principles investigation is carried out on palladium (Pd)-doped armchair graphene nanoribbons (AGNRs) to investigate their structural, electronic and transport properties. The structural analysis of the considered Pd-doped nanoribbons reveals that single Pd doping at the edges of AGNRs results in the most stable configuration. The present findings reveal that the electronic transport properties are strongly dependent on the number of dopant atoms and their positions. Furthermore, it is noted that the proposed two-probe devices exhibit peculiar nonlinear I–V characteristics indicating potential for rectification behavior. Excellent high rectification ratio (RR) and reverse rectification ratio (RRR) are on the order of $$1.8\times 10^{5}$$ and $$9.7\times 10^{4}$$ , respectively, are found for center-Pd-doped 7-AGNRs. The interesting rectifying I–V behavior can be explained by the localization/delocalization effect of frontier orbitals along with the variation of the transmission spectra with the applied bias voltage. These findings indicate that Pd-doped armchair GNRs are a potential candidate for use in next-generation ultralow-power nanoscale switching devices.

High performance polarization-sensitive self-powered imaging photodetectors based on a p-Te/n-MoSe2 van der Waals heterojunction with strong interlayer transition.

In-plane anisotropic two-dimensional (2D) materials offer great opportunities for developing novel polarization sensitive photodetectors without being in conjunction with filters and polarizers. However, owing to low linear dichroism ratio and insufficient optical absorption of the few layer 2D materials, the comprehensive performance of the present polarization sensitive photodetectors based on 2D materials is still lower than the practical application requirements. In this work, after systematic investigation of the structural, vibrational, and optical anisotropies of layer-structured Te nanosheets, a novel polarization-sensitive self-powered imaging photodetector with high comprehensive performance based on a p-Te/n-MoSe2 van der Waals heterojunction (vdWH) with strong interlayer transition is proposed. Owing to the high rectification ratio (104) of the diode, the device shows excellent photovoltaic characteristics. As examples, the photodetectors exhibited an ultrahigh on/off ratio of 105 at a relatively weak light intensity (4.73 mw cm-2), and the highest responsivity of the device could reach 2106 mA W-1 without any power supply. In particular, benefitting from the excellent dichroism properties of Te nanosheets synthesized in this work, the anisotropic ratio of the photocurrent (Imax/Imin) could reach as high as 16.39 (405 nm, 24.2 mw cm-2). This value obtained under zero bias voltage is much greater than that of present 2D material photodetectors even at a bias voltage. In addition, the highest detectivity is 2.91 × 1013 Jones at a low bias voltage of -0.08 V. This work provides a novel building block for high resolution polarization-sensitive photodetection of weak signals in complex environments.

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

Doping-induced large spin-filter behavior and rectification behavior in zigzag graphene nano-ribbon junction

Due to the edge states of zigzag graphene nanoribbon (ZGNR), heterojunctions of p- and n-type doped ZGNRs with either high rectification ratios or high spin-filter efficiencies are constructed. Four ZGNR-based heterojunctions are designed theoretically by replacing the edge carbon atoms of two ZGNR electrodes with boron atoms and nitrogen atoms, respectively. The electron-transport properties and the spin-transport properties are studied by applying non-equilibrium Green's function method combined with first principles calculations. The numerical results show that, such heterojunctions show 100% spin-filter efficiencies in the lower negative bias regime. This excellent spin-filter behavior originates from the localized spin-up sub-bands that lie on the Fermi level of boron-doped electrode and lead to a destructive interference of electrons in the scattering region, thereby preventing the spin-up electrons from entering the electrode and leading to a near-zero spin-up current in lower bias regime. When the dopant boron and nitrogen atoms are hydrogenated, the 100% spin-filter efficiency disappears, but the rectification ratio up to 106 is obtained. This amazing rectification ratio results from the vanishing overlap of conduction bands of the two electrodes for both spin-up and spin-down sub-bands when the absolute value of the negative bias is greater than 0.4 V.

Carrier transport through near-ideal interface for WSe2 van der Waals homojunction diode

Transition-metal dichalcogenides are promising alternatives to conventional materials for next-generation devices owing to their unique characteristics. Because efficient doping is difficult, in designing devices, more than two materials are typically heterogeneously junctioned via van der Waals (vdW) bonds. However, unintended effects at the vdW heterojunction due to lattice mismatch or trap-assisted transport limit the device performance. In this study, we fabricated a vdW homojunction p–n diode with elementally doped WSe2. The device made of pristine WSe2 exhibited forward diode characteristics with an ideal transport characteristic. When WSe2 was doped with the p-dopant bis(trifluoromethane) sulfonimide, the carrier transport mechanism changed from diffusion to tunneling. The device rectified the forward current with a high rectification ratio of 2 × 105 at 300 K. This study provides a comprehensive understanding of the carrier transport mechanism in a high-performance backward vdW homojunction diode.

Optimizing the Electronic Structure of In2O3 through Mg Doping for NiO/In2O3 p-n Heterojunction Diodes.

In2O3 is a wide bandgap oxide semiconductor, which has the potential to be used as an active material for transparent flexible electronics and UV photodetectors. However, the high concentration of unintentional background electrons existing in In2O3 makes it hard to be modulated by the electric field or form p-n heterojunctions with a sufficient band-bending width at the interface. In this work, we report the reduction of the background electrons in In2O3 by Mg doping (Mg-In2O3) and thereby improve the device performance of p-n diodes based on the NiO/Mg-In2O3 heterojunction. In particular, Mg doping compensates the free electrons in In2O3 and reduces the electron concentration from 1.7 × 1019 cm-3 without doping to 1.8 × 1017 cm-3 with 5% Mg doping. Transparent p-n heterojunction diodes were fabricated based on p-type NiO and n-type Mg-In2O3. The device performance was considerably enhanced by Mg doping with a high rectification ratio of 3 × 104 and a remarkable high breakdown voltage of >20 V. High-resolution X-ray photoelectron spectroscopy was used to investigate the interfacial electronic structure between NiO and Mg-In2O3, revealing a type II band alignment with a valence band offset of 1.35 eV and a conduction band offset of 2.15 eV. A large built-in potential of 0.98 eV was found for the undoped In2O3 but decreased to 0.51 eV for 5% Mg doping of In2O3. The NiO/Mg-In2O3 diodes with an improved rectification ratio and wider depletion region provide the possibility of achieving photodetectors with rapid photoresponse.

Enhancing the Diode Characteristics of Pulsed Laser–Deposited n‐MgxZn1−xO/p‐Si Heterojunction: Role of Oxygen Ambient Pressure

Herein, diode characteristics of n‐MgxZn1−xO/p‐Si heterojunctions grown by pulsed laser deposition at different oxygen ambient pressures are investigated. It is found that the heterojunctions grown at lower oxygen growth pressure of 1.0 × 10−2 mbar and below do not show rectifying diode‐like behavior, whereas those grown at higher oxygen pressures at and above 2.5 × 10−2 mbar exhibit perfect diode‐like rectifying characteristics. The diode characteristics are found to improve significantly with increasing oxygen ambient pressure during the growth of MgxZn1−xO film. The current–voltage measurements show that the n‐MgxZn1−xO/p‐Si heterojunction diode grown at a higher oxygen ambient pressure of ≈1.0 × 10−1 mbar has the lowest reverse saturation current of ≈19 nA and highest rectification ratio of ≈1.4 × 104. The capacitance–voltage measurements reveal that the depletion layer width of heterojunction diodes increases manifold with increasing oxygen ambient pressure during the growth of MgxZn1−xO, which is understood in terms of decrease in carrier concentrations in the MgxZn1−xO thin films grown at higher oxygen ambient pressures. The n‐MgxZn1−xO/p‐Si heterojunction diodes, grown at high oxygen ambient pressures, with low reverse saturation current, high rectification ratio, and large depletion width may have potential application in wide‐bandgap nanoelectronic devices and UV enhanced photodetectors.

Record-High-Performance Hydrogenated In-Ga-Zn-O Flexible Schottky Diodes.

High-performance In-Ga-Zn-O (IGZO) Schottky diodes (SDs) were fabricated using hydrogenated IGZO (IGZO:H) at a maximum process temperature of 150 °C. IGZO:H was prepared by Ar + O2 + H2 sputtering. IGZO:H SDs on a glass substrate exhibited superior electrical properties with a very high rectification ratio of 3.8 × 1010, an extremely large Schottky barrier height of 1.17 eV, and a low ideality factor of 1.07. It was confirmed that the hydrogen incorporated during IGZO:H deposition increased the band gap energy from 3.02 eV (IGZO) to 3.29 eV (IGZO:H). Thus, it was considered that the increase in band gap energy (decrease in electron affinity) of IGZO:H contributed to the increase in the Schottky barrier height of the SDs. Angle-resolved hard X-ray photoelectron spectroscopy analysis revealed that oxygen vacancies in IGZO:H were much fewer than those in IGZO, especially in the region near the film surface. Moreover, it was found that the density of near-conduction band minimum states in IGZO:H was lower than that in IGZO. Therefore, IGZO:H played a key role in improving the Schottky interface quality, namely, the increase of Schottky barrier height, decrease of oxygen vacancies, and reduction of near-conduction band minimum states. Finally, we fabricated a flexible IGZO:H SD on a poly(ethylene naphthalate) substrate, and it exhibited record electrical properties with a rectification ratio of 1.7 × 109, Schottky barrier height of 1.12 eV, and ideality factor of 1.10. To the best of our knowledge, both the IGZO:H SDs formed on glass and poly(ethylene naphthalate) substrates achieved the best performance among the IGZO SDs reported to date. The proposed method successfully demonstrated great potential for future flexible electronic applications.

Toward three-dimensional hybrid inorganic/organic optoelectronics based on GaN/oCVD-PEDOT structures

The combination of inorganic semiconductors with organic thin films promises new strategies for the realization of complex hybrid optoelectronic devices. Oxidative chemical vapor deposition (oCVD) of conductive polymers offers a flexible and scalable path towards high-quality three-dimensional inorganic/organic optoelectronic structures. Here, hole-conductive poly(3,4-ethylenedioxythiophene) (PEDOT) grown by oxidative chemical vapor deposition is used to fabricate transparent and conformal wrap-around p-type contacts on three-dimensional microLEDs with large aspect ratios, a yet unsolved challenge in three-dimensional gallium nitride technology. The electrical characteristics of two-dimensional reference structures confirm the quasi-metallic state of the polymer, show high rectification ratios, and exhibit excellent thermal and temporal stability. We analyze the electroluminescence from a three-dimensional hybrid microrod/polymer LED array and demonstrate its improved optical properties compared with a purely inorganic microrod LED. The findings highlight a way towards the fabrication of hybrid three-dimensional optoelectronics on the sub-micron scale.

Hybrid nano-scale Au with ITO structure for a high-performance near-infrared silicon-based photodetector with ultralow dark current

An internal photoemission-based silicon photodetector detects light below the silicon bandgap at room temperature and can exhibit spectrally broad behavior, making it potentially suited to meet the need for a near-infrared pure Si photodetector. In this work, the implementation of a thin Au insertion layer into an ITO/n-Si Schottky photodetector can profoundly affect the barrier height and significantly improve the device performance. By fabricating a nanoscale thin Au layer and an ITO electrode on a silicon substrate, we achieve a well-behaved ITO/Au/n-Si Schottky diode with a record dark current density of 3.7 × 10 − 7 A / cm 2 at − 1 V and a high rectification ratio of 1.5 × 10 8 at ± 1 V . Furthermore, the responsivity has been obviously improved without sacrificing the dark current performance of the device by decreasing the Au thickness. Such a silicon-based photodetector with an enhanced performance could be a promising strategy for the realization of a monolithic integrated pure silicon photodetector in optical communication.

Combining Photomodulation and Rectification in Coordination Molecular Wires Based on Dithienylethene Molecular Junctions

Thin films of photochromic coordination polymers deposited by layer-by-layer technique, based on iron (II) bis-terpyridine-appended dithienylethene blocks, were used to create light-switchable molecular junctions with high rectification ratios. These multilayer films show a modulation of the attenuation factor when exposed to light irradiation

Electrical performance of nanocrystalline graphene oxide/SiO2-based hybrid heterojunction device

In this study, a nanostructure of graphene oxide films was deposited on the surface of silicon oxide to form a hybrid heterojunction diode. The characteristics of dielectric were studied in a wide range of frequencies under the influence of temperature in the range from 223 K to 363 K. The results showed lower and nearly constant values of the dielectric at high frequencies which can be understood under the conception of the inability of the dipole to rotate itself under the influence of high frequency. Moreover, the recorded large capacitance at low frequencies was attributed to the excess capacity value caused by the formed oxide layer. Also, the electrical properties in the dark and under the influence of light illumination were studied in a wide range of temperatures from 303 K to 448 K. The hybrid heterojunction diode exhibited a high rectification ratio at high voltage bias. The extracted series and shunt resistances showed a decrease with increasing temperature, which meant that the characteristics of the device enhanced at a higher temperature. The device also showed a remarkable light sensitivity and the transient photocurrent was detected, confirming the validity of the prepared device for photodiode applications.

Performance improvement of n-TiO2/p-Si heterojunction by forming of n-TiO2/polyphenylene/p-Si anisotype sandwich heterojunction

The n-TiO2/polyphenylene (PPh)/p-Si heterojunction devices were fabricated in which PPh film and TiO2 top layer were grown on p-Si substrates by diazonium modification method and cathodic electrodeposition, respectively. The XPS, UV–vis diffuse reflectance and STM analyses of the films were performed. After the characterization of deposited films and the fabrications of n-TiO2/PPh/p-Si sandwich devices, the electrical measurements of nine devices were carried out from the current–voltage (I–V) characteristics, at room temperature. The I–V characteristics of n-TiO2/PPh/p-Si heterojunctions were compared with TiO2/p-Si heterojunctions, one of them was analysed in more detailed and it was observed that the n-TiO2/PPh/p-Si gave better performance than TiO2/p-Si heterojunctions such that lower ideality factor, higher rectification ratio and more stable reverse current characteristics. Then, the main device parameters of n-TiO2/PPh/p-Si were compared with many devices reported in literature based on TiO2/p-Si device and TiO2 preparation techniques. Furthermore, the rectification ratio of n-TiO2/PPh/p-Si heterojunction was 9.42 × 105, while it was 5.80 × 102 for TiO2/p-Si heterojunction. Later, the capacitance-voltage (C–V) and conductance-voltage (G-V) measurements of the n-TiO2/PPh/p-Si heterojunction was performed depending on applied frequency and bias and it was observed that the values of capacitance and conductance were found a strongly function of bias voltage.

Interfacial ZnS passivation for improvement of transparent ZnO/CuI diode characteristics

To fabricate a n-ZnO/p-CuI heterojunction diode with a high rectification ratio at a large junction area, γ-CuI film was spin-coated on ZnO. Since the n-ZnO/p-CuI diode showed a rectification ratio as small as 2.38 × 102, the ZnS interfacial layer was prepared by successive ionic layer adsorption and reaction. By placing a ZnS layer between the n-ZnO/p-CuI, the rectification ratio from the diode increased to 1.71 × 107 at a junction area of 1 cm2. Modification of the valence band offset and the conduction band offset of the n-ZnO/p-CuI junction in the presence of the interfacial ZnS layer may facilitate carrier transport between ZnO and CuI. In addition, it was confirmed that two types of defects (oxygen vacancy and unpaired electron trapped on an oxygen vacancy) were reduced by insertion of an interfacial ZnS layer. A significant improvement in the rectification ratio resulted from the large decrease in the reverse current in the ZnO/CuI diode by a reduced amount of oxygen vacancies. Therefore, the improvement of band alignment with the decrease in the interfacial defects by the introduction of wide bandgap ZnS passivation layer enhanced the electrical characteristics of ZnO/CuI diode.

Transition metal dichalcogenides thyristor realized by solid ionic conductor gate induced doping

Transition metal dichalcogenides (TMDCs) are promising for future electronic and optoelectronic applications, such as field effect transistors (FETs), for their high carrier mobility with a thin layer, wide bandgap, and organic-like flexibility. However, background doping and unipolar electrical characteristics are commonly observed in TMDCs and their based FETs due to the naturally inevitable vacancy defects, which limit their application in electronics and optoelectronics systems. Here, taking MoS2 as an example, in a TMDC FET, ambipolar properties were achieved at room temperature by introducing an amorphous solid ionic conductor lithium tantalate (LiTaO3) as the gate dielectric, which could guarantee the modulation of the Fermi level in the MoS2 channel by the gate electric field. Based on the modulation mechanisms by the solid ionic conductor-gated electric field for the transformation of conduction mode, the three-terminal device exhibits a gate-controlled rectifying, that is, thyristor performance with a high rectification ratio over 300 obtained at a low gate voltage of 2 V. The present results show the great potential of TMDCs in future logic and other electronic device applications.

Bipolar resistive switching with unidirectional selector function in nitride/oxide heterostructures

In this work, we propose a self-rectifying Ni/SiNx/HfO2/p++Si resistive memory device to alleviate the sneak-path current occurring in crossbar array. The bilayer (Ni/SiNx/HfO2/p++Si) device exhibits a much higher rectification ratio (>104) in the low-resistance state for DC sweep mode and pulse mode than single-layer devices (Ni/SiNx/p++Si and Ni/HfO2/p++Si). The suppressed current of the bilayer device can be explained by the high Schottky barrier of the HfO2 layer under a negative bias. The modified read bias scheme in the crossbar array structure ensures a large number of word line (∼3971 at a read margin of 10%) using the advantage of the high rectification of the bilayer device. The bilayer device with the proposed read bias scheme is promising for high-density memory applications.

Multilayer InSe-Te van der Waals Heterostructures with an Ultrahigh Rectification Ratio and Ultrasensitive Photoresponse.

Multilayer van der Waals (vdWs) semiconductors have promising applications in high-performance optoelectronic devices. However, photoconductive photodetectors based on layered semiconductors often suffer from sizeable dark currents and high external driving bias voltages. Here, we report vertical van der Waals heterostructures (vdWHs) consisting of multilayer indium selenide (InSe) and tellurium (Te). The multilayer InSe-Te vdWH device shows a record high forward rectification ratio greater than 107 at room temperature. The vdWH device achieves an ultrasensitive and broadband photoresponse photodetector with an ultrahigh photo/dark current ratio over 104 and a high detectivity of 1013 Jones under visible light illumination with weak incident power. Moreover, the vdWH device has a photovoltaic effect and can function as a self-powered photodetector (SPPD). The SPPD is also ultrasensitive to a broadband spectrum ranging from 300 to 1000 nm and is capable of detecting weak light signals. This work offers an opportunity to develop next-generation electronic and optoelectronic devices based on multilayer vdWs materials.

A 1.86-kV double-layered NiO/ β -Ga2O3 vertical p–n heterojunction diode

In this Letter, high-performance vertical NiO/β-Ga2O3 p–n heterojunction diodes without any electric field managements were reported. The devices show a low leakage current density and a high rectification ratio over 1010 (at ±3 V) even operated at temperature of 400 K, indicating their excellent thermal stability and operation capability at high temperature. Given a type-II band alignment of NiO/β-Ga2O3, carrier transport is dominated by the interface recombination at forward bias, while the defect-mediated variable range hopping conduction is identified upon strong reverse electric field. By using the double-layer design of NiO with a reduced hole concentration of 5.1 × 1017 cm−3, the diode demonstrates an improved breakdown voltage (Vb) of 1.86 kV and a specific on-resistance (Ron,sp) of 10.6 mΩ cm2, whose power figure of merit (Vb2/Ron,sp) has reached 0.33 GW/cm2. The high breakdown voltage and low leakage current are outperforming other reported Ga2O3 based p–n heterojunctions and Schottky barrier diodes without field plate and edge termination structures. TCAD simulation indicates that the improved Vb is mainly attributed to the suppression of electric field crowding due to the decreased hole concentration in NiO. Such bipolar heterojunction is expected to be an alternative to increase the breakdown characteristics of β-Ga2O3 power devices.