Schottky Emission Mechanism Research Articles

Influence of 700 keV O3+ ion implantation on current transport properties of Cr/p-GaN SBD’s

In the present study we show a detailed investigation into the influence of 700 keV O3+ ion implantation in Cr/p-GaN SBDs on electrical characteristics / current transport properties. Also the damage events along the trajectory of the ion beam were quantitatively estimated through SRIM and TRIM simulations. The Current-voltage (I-V) characteristics were analyzed using different methods such as Cheung and Cheung's method and Norde’s method to obtain different electrical parameters. The values of n and ϕB decrease up to a fluence of 1 × 1014 ions cm−2, and show a fractional increase at a fluence of 1 × 1015 ions cm−2. Further, a drastic increase in values of series resistance (RS ) of SBDs with an increase in fluence was observed. In the forward-bias voltage regions, the Cr/p-GaN SBDs conduction mechanism shows an increasingly ohmic behavior with an increase in fluence, which may be attributed to thermally generated carriers. At low voltage, the reverse current conduction mechanism is due to Poole-Frenkel emission. For the high voltage region, Schottky emission mechanism becomes more prominent. The changes in electrical parameters are closely related to the defect and damage profiles estimated through SRIM/TRIM simulations, which are strongly dependent on the dose of the 700 keV O3+ ion implantation. Additionally, we found that at high doses, the charge transport mechanism changes, with additional defects affecting not only the thermionic emission mechanism but also various current transport mechanisms.

Understanding the Reversible Transition of Unipolar and Bipolar Resistive Switching Characteristics in Solution-Derived Nanocrystalline Au-Co3O4 Thin-Film Memristors.

Nanocrystalline Au-Co3O4 thin films were fabricated through a facile solution-processing method, and voltage-polarity-dependent resistive switching (RS) characteristics including variability of Set/Reset voltages, stability of cycling endurance, and carriers transport mechanism were studied in the Pt/Au-Co3O4/Pt memory devices. The switching voltages of the Set and Reset processes in the bipolar RS memristors exhibited lower variability as compared to the unipolar resistance switching devices. Moreover, the switching performance of cycle-to-cycle endurance in bipolar mode had a smaller fluctuation than those of unipolar switching behavior. Based on the current-voltage curve fitting analysis, it was found that Ohmic-conduction behaviors dominated the carriers transport of low-resistance state regardless of unipolar or bipolar switching behaviors. The carrier transport of high resistance state was governed following Poole-Frenkel emission and Schottky emission mechanisms in the unipolar and bipolar switching modes, respectively. The physical switching mechanism of Pt/Au-Co3O4/Pt memory devices was proposed using the model by means of growth and disruption of conducting filaments, involved in memory effects of thermochemical mechanism and valence change mechanism in the unipolar and bipolar RS, respectively. The proposed model following the finite element method revealed the roles of electrical field distribution and temperature gradient to further clarify the RS mechanism. Our results open a door for understanding and optimizing oxide-based thin-film resistance switching memory devices.

High performance low power multilevel oxide based RRAM devices based on TiOxNy/Ga2O3 hybrid structure

In this study, the resistive memory devices with Ag/TiOxNy/Pt structure and Ag/TiOxNy/Ga2O3/Pt structure are fabricated. The results showed that they exhibit typical resistive behaviors as well as excellent cycling and retention characteristics (>104 s). Especially, the double-layer device with Ga2O3 layer exhibits superior resistive behavior, which has a larger storage window (ON/OFF ratio >105), a smaller set voltage (0.17 V) and a reset voltage (−0.057 V), and lower power consumption (21.7, 0.17 μW) compared with the single-layer device. Furthermore, the Ag/TiOxNy/Ga2O3/Pt device demonstrates ultraviolet light (UV-365 nm)-dependent resistance state (RS), which is advantageous for multilevel memory cells. As the intensity of UV light increases, eight high resistance state (HRS) levels are produced. Finally, the conductive mechanism for both device structures is discussed, and it is found that the conductive filaments mechanism dominates in the low resistance state. However, for the HRS, the single-layer TiOxNy device is dominated by the space charge-limited conduction mechanism, and the double-layer TiOxNy/Ga2O3 device is dominated by the Schottky emission mechanism.

NDR effect and negative-set/reset phenomenon in core-shell structure-based memristor under the effect of humidity

The potential applications of memristors in the post-Moore era of rapidly developing next-generation artificial intelligence and high-frequency communication technologies are immense. The effects on the resistive switching (RS) characteristics based on Ag Salt@TiO2 memristive device with a nano core-shell structure under different relative humidity (RH) environments have been investigated in this work. Negative-set/reset phenomena occurs in negative voltage region due to excessive growth of conductive filaments (CFs). When the CF returns to normal growth, the current suddenly decreases in the positive high voltage area at lower humidity, which can be explained by the dissolution and growth hindrance of the CFs. Furthermore, the coexistence of negative differential resistance (NDR) and bipolar RS at room temperature can be regulated by adjusting humidity. The current conduction mechanism of the device in both dry and humid environments were fitted using the ohmic conduction mechanism, space charge-limited current (SCLC) conduction mechanism, and Schottky emission mechanism.

Improvement of memristive switching of Pb(Zr0.52Ti0.48)O3/Nb:SrTiO3 heterostructures via La doping

The ferroelectric memory with superior stability and high operating speed has broad development prospects in areas such as neural computing and information storage. An effective strategy to improve the performance of the resistive switching (RS) of the ferroelectric memory is to improve the conductivity of ferroelectric thin films while maintaining their ferroelectric properties, because there is a competition between ferroelectric properties and conductivity in the RS behavior. Herein, we prepared La-doped Pb(Zr0.52Ti0.48)O3 (PLZT) thin films on the Nb:SrTiO3 (NSTO) substrate. By controlling La concentration, a compromise between ferroelectricity and conductivity was achieved. The RS on/off ratio reached 2.6 × 104 doped with 2 mol% La. Moreover, the conduction mechanism changes from the Schottky emission controlling PZT/NSTO interface to the coexistence of Schottky emission and space charge-limited mechanism in the PLZT/NSTO heterostructures. The results reveal that the effective matching of the ferroelectricity and conductivity of ferroelectric thin films is necessary for obtaining high RS on/off ratio, which is helpful to the accurate design of high-performance ferroelectric memory devices.

Stable resistive switching behavior of polyvinyl alcohol coating film-based memristor under multiple operating voltages by doping AgNWs

The integration of memristive effect devices for both information storage and computation can enhance the efficiency and performance of artificial intelligence (AI) systems，the memristors based on various polymers as functional layers show high application prospects. This research introduces 5 wt% silver nanowires (AgNWs) doping into the polyvinyl alcohol (PVA) memristor device, which enables stable resistive switching (RS) behavior across multiple operating voltages. Defects from PVA and AgNWs are counterbalanced by Ag ions stimulated by AgNWs and Ag top electrode, thus reducing conductive path randomness. The device demonstrates excellent cycle durability for 300 cycles and data retention for up to 104 s. Analysis of the I-V characteristic curve reveals that the current conduction mechanism is mainly related to Ohmic conduction, Space-charge-limited conduction (SCLC), and Schottky emission mechanisms. The AgNWs simplify the structure of conductive filaments (CFs) and facilitate the formation and breakage of CFs dominated by Ag atoms, leading to the conversion between HRS and LRS of the device.

Resistive switching characteristics and mechanism of W/TiO2/ITO devices

In recent years, titanium oxide (TiO2)-based memristors have come under widespread investigation due to their compatibility with CMOS technology and their potential use as the forthcoming nonvolatile memories. However, the practical application of these devices requires a detailed understanding of their switching mechanism. This study examined the resistive switching and conduction mechanism of titania films on an Indium tin oxide (ITO) substrate with tungsten (W) serving as the top electrode (TE). The thin film of TiO2 was fabricated by solution processing and spin coating technique. The sol was prepared using titanium tetra isopropoxide (TTIP) and ethanol. Optical characterization was done using UV–Visible transmission spectroscopy. From the tauc plot, the band gap of films treated at 250 °C and 400 °C was found to be 3.37 eV and 3.29 eV, respectively. From the electrical analysis, a pinched hysteresis current–voltage curve was obtained, and the device exhibits stable, reversible, forming-free, and interface type resistance-switching characteristics.The homogeneous switching observed in this device is caused by oxygen vacancy-induced barrier modulation at the metal-oxide interface. The I-V data were fitted to various conduction mechanismsand it was found that ohmic conduction and Schottky emission mechanism (SE) were dominant in the low and high field regions, respectively, for both HRS and LRS.

Dielectric response of high-κ hafnium oxide under finite electric field: nonlinearities from ab initio and experimental points of view.

Herein, we report on the dielectric-voltage nonlinearities under a constant electric field in metal insulator metal (MIM) capacitor-based hafnium oxide (HfO2) with respect to the frequency range. Via the Schottky emission mechanism obtained from the current-voltage characteristic (I-V), we calculated the optical dielectric constant εr,opt for different external DC bias values. The extracted εr,opt revealed a quadratic dependence on the applied external field. This confirmed that such dependence is a common feature of high-κ oxides in the low and high frequency ranges. The results were correlated with the ab initio calculations using the finite field (FF) method as implemented in the CRYSTAL 17 code. Good agreement between the results from the FF method, I-V plots, as well as the UV-visible spectrometry is observed. To assess any change in the dielectric constant upon the application of an external electric field, several parameters such as exchange-correlation functional, basis sets (BSs), as well as supercell expansion factor (N) were tested. The corresponding parameters have a great influence on the macroscopic electron density and voltage along the field direction and thus on the optical response. For N > 2 and rich basis sets, the hybrid functional B3LYP revealed good agreement with the experimental results as compared to other Hamiltonian's forms such as LDA, PW-GGA and HF.

Fowler-Nordheim tunneling in β-Ga2O3/SrRuO3 Schottky interfaces

Interfaces in heterostructures always emerge as prototype electronic devices with tunable functionality. The fundamental properties of these interfaces can be finely manipulated by epitaxy engineering. Recently, heterostructures based on Ga2O3, an ultra-wide bandgap semiconductor, have been reported for use in high powered device applications. Herein, we will demonstrate a heterostructure of β-Ga2O3/SrRuO3 integrated on c-plane sapphire, where the high density of edge dislocations are evidenced in the heterostructure interfaces. Apart from the dominant Schottky emission mechanism, Fowler-Nordheim tunneling is also revealed by leakage current analysis, which may be ascribed to the edge dislocations at the interfaces. These results boost the basic understanding of ultra-wide bandgap materials and devices.

Influence of tin oxide (SnO2) interlayer on the electrical and reverse current conduction mechanism of Au/n-InP Schottky junction and its microstructural properties

The microstructural and current-voltage (I-V) characteristics of the prepared Au/SnO2/n-InP heterojunction (HJ) with an e-beam evaporated tin oxide (SnO2) film as an interlayer between the Au and InP substrate have been explored. The X-Ray diffraction and transmission electron microscopy results confirm the formation of the SnO2 thin film on InP surface. Then, the Au/SnO2/n-InP HJ diode is prepared and explored its electrical properties by the I-V approach. Low reverse leakage current is noted for HJ diode than the Au/n-InP Schottky junction (SJ). Higher barrier height (BH) is attained for the HJ compared to the SJ, which indicates that the insertion of SnO2 interlayer leads to an increase in the BH of SJ. Further, the BH is evaluated for the SJ and HJ diodes by Hernandez and Cheung's methods and matched with one another. Results exhibit that the interface state density (NSS) of HJ is less than the SJ, suggesting that the use of the SnO2 layer plays a key role in reducing NSS. Analysis of the reverse leakage current transport suggested the dominance of Poole-Frenkel emission in the lower bias region while the Schottky emission mechanism governs at upper bias region in both the SJ and HJ diodes. These results could provide expedient information of SnO2 interlayer for the design of metal/interlayer/semiconductor or heterojunction devices.

High Curie temperature BiFeO3-BaTiO3 lead-free piezoelectric ceramics: Ga3+ doping and enhanced insulation properties

BiFeO3-BaTiO3 is a promising high-temperature lead-free piezo-ceramics due to its high Curie temperature (TC > 500 °C) and excellent piezoelectric properties. However, a high leakage current was often detected in this system, which severely affects its applications. In this work, the 0.7BiFe(1−x)GaxO3-0.3BaTiO3 (BFGax-BT, 0.00 ≤ x ≤ 0.10) system was designed to reveal the reason of leakage-current density decreased by their leakage mechanism. Because of the suppression of generation of Fe2+ and oxygen vacancy (VO∙∙), the leakage mechanism from space charge limited conduction mechanism found in Ga-free BF-BT ceramics turns into Ohmic conduction and Schottky emission mechanism as Fe3+ was replaced with Ga3+. A good combination of piezoelectric properties (d33 = 174 pC N−1 and kp = 29%) and high Curie temperature (TC = 497 °C) was achieved in the BFGa0.06-BT ceramic owning the lowest leakage-current density. This work will provide the clues for preparing the high insulation and high piezoelectric performance BF-BT-based ceramics by suppressing the valence change of Fe3+ and VO∙∙ appearance.

Copper ion beam emission in solid electrolyte Rb4Cu16I6.5Cl13.5

Copper ion conducting solid electrolyte Rb4Cu16I6.5Cl13.5 was prepared by means of mechano-chemical method. The structure and morphology of the powder was investigated by x-ray diffraction and scanning electron microscopy. The grain size was estimated to be 0.2–0.9 μm and the ionic conductivity at room temperature was approximately 0.206 S/cm. The solid electrolyte Rb4Cu16I6.5Cl13.5 was exploited for copper ion beam generation. The copper ion emission current of several nA was successfully obtained at acceleration voltages of 15 kV and temperature of 197 °C in vacuum of 2.1 × 10−4 Pa. A good linear correlation between the logarithmic ion current (log I) and the square root of the acceleration voltage (U acc) at high voltage range was obtained, suggesting the Schottky emission mechanism in the process of copper ion beam generation.

Compact Modeling of the Switching Dynamics and Temperature Dependencies in TiOₓ Memristors—Part II: Physics-Based Model

In the second part of this series, we propose a physics-based model for describing the temperature dependence of TiO x -based memristors, both switching and static. We show that the current–voltage ( ${I}$ – ${V}$ ) characteristics of memristor in the nonswitching regime, indicating a Schottky emission mechanism, can be described by minor modifications to the Schottky current equation. This leads to a physics-based static ${I}$ – ${V}$ compact model. Simultaneously, we show that the temperature dependence of the switching dynamics model parameters naturally emerges as a mere scaling factor from the static ${I}$ – ${V}$ model. This is a computationally efficient approach, which does not require any additional parameters to extend the switching dynamics model for incorporating thermal dependence.

Resistive Switching Effects of Crystal‐Ion‐Slicing Fabricated LiNbO3 Single Crystalline Thin Film on Flexible Polyimide Substrate

AbstractThe fabrication process and resistive switching properties of flexible single crystalline LiNbO3 (LN) thin films are reported in this paper. Single crystalline LN thin films are transferred onto polyimide (PI) substrate by crystal‐ion‐slicing (CIS) technique using benzocyclobutene (BCB) as bonding layer. Low energy Ar+ irradiation is carried out to introduce a layer with high concentration oxygen vacancies. Uniform and stable resistive switching behaviors are observed in different memristor cells on the same thin film, which can be attributed to the single crystalline properties of the fabricated LN thin films. The on/off ratio is almost the same even when the LN thin film is bended either to different radii or thousand times. Thus, based on CIS technique and Ar+ irradiation, the fabrication method of flexible single crystalline thin films for flexible memristor is established. These results indicate that single crystalline LN thin film on PI substrate is a promising candidate structure for flexible memristor devices. A novel conduction model combined filamentary mechanism and Schottky emission mechanism is proposed to explain the resistive switching behavior.

Variation of leakage current conduction mechanism by heat treatment in Bi-based lead-free piezoelectric ceramics

The leakage current mechanism in the as-sintered and quenched 0.75BiFeO3–0.25BaTiO3 (0.75BF–0.25BT) ceramics is evaluated by the space-charge-limited current (SCLC), Poole–Frenkel (P–F) emission, Schottky (ST) emission, and Fowler–Nordheim (F–N) tunneling mechanism. The discrepancy observed in the optical dielectric constant of BF and BT between the reported value and the values calculated from the P–F and ST emission plots suggests that the P–F emission and ST emission mechanisms do not contribute to the leakage current behavior of the 0.75BF–0.25BT ceramics. Subsequently, F–N tunneling is observed under a high electric field in the as-sintered 0.75BF–0.25BT ceramics, whereas the direct tunneling effect is exhibited throughout the measured electric field in the quenched ceramics. The SCLC mechanism is dominant in both the as-sintered and quenched 0.75BF–0.25BT ceramics. A change from Ohmic conduction to trap-filled-limit conduction is observed with an increase in the applied electric field in the as-sintered ceramics, whereas the quenched ceramics only revealed Ohmic conduction over the entire range of the measured electric field. The different behaviors exhibited in the SCLC mechanism between the as-sintered and the quenched ceramics imply that the conduction mechanism can be controlled by heat treatment.

Enhanced resistive switching performance in bilayer Pt/TiO2/Co3O4/Pt memory device

In this work, the bilayer Pt/TiO2/Co3O4/Pt and single-layer Pt/TiO2/Pt memory devices were fabricated for investigating their resistive switching characteristics. The statistical switching parameters revealed the enhanced resistive switching performance in the bilayer Pt/TiO2/Co3O4/Pt device, for instance, more centralized operating voltages and current, as well as lower power consumption. The analysis of conductive mechanisms showed that the Schottky emission and Ohmic mechanisms were responsible for the OFF and ON states of the Pt/TiO2/Co3O4/Pt memory devices. The conductive filament mode combined with the fitting results of conductive mechanisms was used to illustrate the resistive switching effect, which provided a microscopic model for a deeper understanding of switching behavior in bilayer devices. Our results indicated that switching properties of TiO2-based resistive random access memory (RRAM) could be improved by inserting a Co3O4 layer.

Implementation of synaptic learning rules by TaO x memristors embedded with silver nanoparticles* *Project supported by the National Natural Science Foundation of China (Grant No. 61674038), the Natural Science Foundation of Fujian Province, China (Grant No. 2019J01218), the Fund from the Fujian Science and Technology Innovation Laboratory for Optoelectronic Information of China (Grant No. 2021ZR145), and the Science Fund from

As an alternative device for neuromorphic computing to conquer von Neumann bottleneck, the memristor serving as an artificial synapse has attracted much attention. The TaO x memristors embedded with silver nanoparticles (Ag NPs) have been fabricated to implement synaptic plasticity and to investigate the effects of Ag NPs. The TaO x memristors with and without Ag NPs are capable of simulating synaptic plasticity (PTP, STDP, and STP to LTP), learning, and memory behaviors. The conduction of the high resistance state (HRS) is driven by Schottky-emission mechanism. The embedment of Ag NPs causes the low resistance state (LRS) conduction governed by a Poole–Frenkel emission mechanism instead of a space-charge-limited conduction (SCLC) in a pure TaO x system, which is ascribed to the Ag NPs enhancing electric field to produce additional traps and to reduce Coulomb potential energy of bound electrons to assist electron transport. Consequently, the enhanced electric fields induced by Ag NPs increase the learning strength and learning speed of the synapses. Additionally, they also improve synaptic sensitivity to stimuli. The linearity of conductance modulation and the reproducibility of conductance are improved as well.

Enhanced reliability through regulation of electrode resistance in indium tin oxide/HfOx/TiN resistive memories

In this work, three indium tin oxide (ITO) films with distinct resistance values were realized by optimizing the deposition process, and X-ray photoelectron spectroscopy was performed to confirm the origin of resistance variation in the different ITO films. Three ITO/HfOx/TiN (IHT) devices were correspondingly constructed by capping the distinct ITO films applied as a top electrode. A series of reliability measures indicated that the IHT stack capping ITO films with high resistance value (RTE, ~600 Ω) demonstrated better performance. For example, endurance of up to 105 sweep cycles, compared with other stacks capping ITO films with low RTE (~300 Ω or 50 Ω). Furthermore, the Schottky emission mechanism was confirmed through fitting of I-V-curves in the HRS, and the carrier conduction was determined primarily by an Ohmic mechanism in the LRS.

Radiation sustenance of HfO2/β-Ga2O3 metal-oxide-semiconductor capacitors: gamma irradiation study

β-Ga2O3 is an interesting new generation wide bandgap semiconductor for power device applications. The gamma irradiation was performed on the HfO2/β-Ga2O3-based metal-oxide-semiconductor capacitors at 1 kGy and 200 kGy doses. The leakage current density variation at −1 V is 3.47 × 10−7 A cm−2, 5.90 × 10−7 A cm−2 and 4.91 × 10−6 A cm−2 for the pristine, 1 kGy and 200 kGy devices, respectively. In the case of substrate injection, the Schottky emission mechanism appears to be dominant in the 0.65 to 2.0 MV cm−1 electric field range. The barrier heights (Ni/HfO2/β-Ga2O3) 0.95 eV, 0.86 eV and 0.83 eV were extracted from Schottky emission for the pristine, 1 kGy and 200 kGy doses, respectively. However, as the dose increases to 200 kGy, the charge-trapping favors the trap-assisted Poole–Frenkel (PF) tunneling mechanism. In this case, the PF emission mechanism seems to be dominant for the pristine and 1 kGy in the range of 2.0–4.0 MV cm−1, whereas for 200 kGy it is 1.45 to 4.0 MV cm−1 which indicates that the defect assisted PF tunneling is predominant at 200 kGy irradiation dose. There is an increase in the density of oxide traps (Dot) changes from 1.14 × 1012 cm−2 eV−1 to 1.47 × 1012 cm−2 eV−1, and the density of interface traps has increased from 1.95 × 1011 cm−2 eV−1 to 3.80 × 1011 cm−2 eV−1 for the pristine and 200 kGy samples, respectively. The peaks of Photoluminescence show that the three bands of defects centered at 3.0, 2.7 and 2.2 eV. These peaks have possibly arisen from the vacancies of oxygen. At 200 kGy high dose, the defect band emissions were found at 2.9, 2.6 eV and a broad emission at 2.1 eV indicates the increase in the denisty of oxide-trapped charges within the HfO2 layer.

Leakage Current Conduction Mechanism of Au-Pt-Ti/ HfO2-Al2O3/n-InAlAs Metal-Oxide-Semiconductor Capacitor under Reverse-Biased Condition

Au-Pt-Ti/high-k/n-InAlAs metal-oxide-semiconductor (MOS) capacitors with HfO2-Al2O3 laminated dielectric were fabricated. We found that a Schottky emission leakage mechanism dominates the low bias conditions and Fowler–Nordheim tunneling became the main leakage mechanism at high fields with reverse biased condition. The sample with HfO2 (4 m)/Al2O3 (8 nm) laminated dielectric shows a high barrier height ϕB of 1.66 eV at 30 °C which was extracted from the Schottky emission mechanism, and this can be explained by fewer In–O and As–O states on the interface, as detected by the X-ray photoelectron spectroscopy test. These effects result in HfO2 (4 m)/Al2O3 (8 nm)/n-InAlAs MOS-capacitors presenting a low leakage current density of below 1.8 × 10−7 A/cm2 from −3 to 0 V at 30 °C. It is demonstrated that the HfO2/Al2O3 laminated dielectric with a thicker Al2O3 film of 8 nm is an optimized design to be the high-k dielectric used in Au-Pt-Ti/HfO2-Al2O3/InAlAs MOS capacitor applications.