Schottky Barrier Interface Research Articles

Silicon flexoelectronic transistors

It is extraordinarily challenging to implement adaptive and seamless interactions between mechanical triggering and current silicon technology for tunable electronics, human-machine interfaces, and micro/nanoelectromechanical systems. Here, we report Si flexoelectronic transistors (SFTs) that can innovatively convert applied mechanical actuations into electrical control signals and achieve directly electromechanical function. Using the strain gradient-induced flexoelectric polarization field in Si as a "gate," the metal-semiconductor interfacial Schottky barriers' heights and the channel width of SFT can be substantially modulated, resulting in tunable electronic transports with specific characteristics. Such SFTs and corresponding perception system can not only create a high strain sensitivity but also identify where the mechanical force is applied. These findings provide an in-depth understanding about the mechanism of interface gating and channel width gating in flexoelectronics and develop highly sensitive silicon-based strain sensors, which has great potential to construct the next-generation silicon electromechanical nanodevices and nanosystems.

Unusual Contact Properties at the Metal–2D Perovskite Interface: The Crucial Role of Naturally Formed Buffer Layer in 2D Perovskite

The contact properties of two-dimensional (2D) perovskites with electrode can severely affect the device performance. In this work, we studied the contact properties of Cs2PbI2Cl2 with different metals (Al, Ag, Au, Pd, Ir, and Pt). A naturally formed buffer layer in Cs2PbI2Cl2 at the interface plays a crucial role in affecting the interface electronic properties. Two stacking patterns are constructed according to their symmetry. Typical Schottky contacts are observed in type II contacts with a strong Fermi level pinning (FLP) effect, while unusual FLP is observed in type I contacts. Remarkably, Ohmic contacts are obtained in Pd/Ir/Pt-Cs2PbI2Cl2 type I contacts. The influence of interfacial coupling behaviors to the FLP is revealed. This study shows that through judicious device architecture design, tunable interfacial tunneling and Schottky barriers can be achieved in metal-Cs2PbI2Cl2 contacts, which would provide guidance in developing more effective electronic nanodevices based on Cs2PbI2Cl2 and its analogues.

Coexistence of Write Once Read Many Resistive Switching with Negative Differential Resistance in Bi‐Rich Bi12FeO20 Ideal Sillenite

The materials showing write once read many (WORM) types of resistive switching characteristics are potential candidates for permanent storage. The negative differential resistance‐based memory devices have the potential to perform like nonlinear systems together with resistive switching simultaneously. The successful synthesis of Bi‐rich Bi12FeO20 sillenite material as phase pure thin film on fluorine tin oxide (FTO) using a solution process together with thermally deposited copper (Cu) as the top contact is demonstrated. Cu/Bi12FeO20/FTO/Glass resistive random‐access memory (RRAM) devices show the WORM characteristics with Ion/Ioff ratio103 and negative differential resistance simultaneously. Further, Bi12FeO20 active material also shows nonvolatile characteristics with analog switching for 200 cycles or more with large retention time, ≈5 × 103 s, and endurance for 103 cycles, substantiating the stability of the device. The space charge limited conduction and Schottky mechanisms explain the formation of a conductive filament in a high resistance state (HRS) and rupturing of a conductive filament in a low resistance state (LRS). The observed negative differential resistance is attributed to trapping, detrapping, and Schottky barrier interface between the top electrode and active layer together with ambient humidity.

Ultrahigh energy storage capacity in multilayer-structured cellulose-based dielectric capacitors caused by interfacial polarization-coupled Schottky barrier height

The interfacial polarization-couples Schottky barrier height between BT particles and the C8P2 matrix strongly enhanced the energy storage capacity of this cellulose-based flexible capacitors.

Interface formation and Schottky barrier height for Y, Nb, Au, and Pt on Ge as determined by hard x-ray photoelectron spectroscopy

Development of a robust, thin, hole-blocking (n+) contact on high purity germanium (HPGe) has been the main challenge in the development of Ge-based radiation sensors. Yttrium has been reported to be a viable hole-blocking contact on HPGe, and detectors with low leakage have been fabricated. Niobium has also been considered as a potential hole-blocking contact due to its low work function. Here, we investigate interface chemistry and the Schottky barrier height of Y and Nb, as well as electron-blocking contacts Au and Pt, on Ge(100) surfaces using hard x-ray photoelectron spectroscopy. We find a barrier height of 1.05 ± 0.10 eV for Y/HPGe, confirming the formation of a hole-blocking barrier. For Nb/HPGe, the barrier height of 0.13 ± 0.10 eV demonstrates that the interface is not hole-blocking. The Schottky barrier of Au and Pt was found to be 0.45 ± 0.10 and 0.51 ± 0.10 eV, respectively.

Defective ZrO2−x supported Ru nanoparticles as a Mott–Schottky photocatalyst for efficient ammonia synthesis under ambient conditions

The supported Ru co-catalyst induces upward band bending in the defective ZrO2−x, forming an interfacial Schottky barrier that facilitates the separation of photogenerated charge carriers and provides energetic electrons for nitrogen activation.

Realistic Multidimensional Optoelectrical Modeling Guide for Copper Indium Gallium Diselenide Solar Cells

Herein, an optoelectrical model is presented for copper indium gallium diselenide (CIGSe) solar cells in COMSOL Multiphysics, capable of multidimensional simulations, and it is applied to ultrathin (500 nm absorber thickness) solar cells. First, the modeling approach is shown. Special attention is paid to back contact materials, interface states, and defect application and their impact on the current–voltage (J–V) characteristics. To address whether the back contact is Schottky or Ohmic, the influence of the Schottky barrier height, recombination velocity, and interface states is shown. Then, the additional application of an acceptor defect gradient at the absorber back and a donor defect density distribution at the p–n junction is investigated. The results of these parameter adjustments are discussed, and the trends are shown to enable fast fitting of experimental J–V curves. Finally, the results are compared to the experimental J–V curves for indium tin oxide and Mo back contact, and challenges encountered are discussed while fitting. The optoelectrical model for CIGSe solar cells, established in two dimensions here, paves the way for comprehensively describing 2D and 3D solar cell structures, e.g., nanotextured or microsolar cells, as well as for considering different absorber thicknesses.

In Quest of Low‐Leakage Dynamic Random Access Memory Enabled by Doped TiO2 Dielectrics

AbstractHigh permittivity rutile TiO2 has been regarded as a promising candidate for the capacitor dielectric in ultra‐scaled dynamic random access memory (DRAM), but its low band gap and low interfacial Schottky barrier cause the bothering leakage current problem. It is in principle possible to tune the electrode Fermi level to the mid‐gap of TiO2 for leakage current reduction. In this work, the generalized gradient approximation (GGA)‐1/2 method is shown as a viable first‐principles approach to predict the Schottky barriers of TiO2 based capacitors. Through RuO2/TiO2/RuO2 and IrO2/TiO2/IrO2 full capacitor calculations, the impact of trivalent cation dopants (Al, Ga, La, and Y) on the Schottky barrier tuning is systematically studied. Among the four dopants, it is discovered that Y doping is most effective in hindering the formation of oxygen vacancies by analyzing formation energy and crystal orbital Hamilton population. Y‐doped rutile TiO2 is a promising material for next‐generation high capacitance and low leakage DRAM capacitors.

Effective Schottky barrier height and interface trap density reduction engineering using 2-dimensional reduced graphene oxide interlayer for metal-interlayer-semiconductor contact structure

The contact resistance at the metal-semiconductor (MS) interface has become the foremost challenge to ensuring high performance in nanoelectronics as devices are scaled down. A metal-interlayer-semiconductor (MIS) contact structure is a promising technique for Fermi-level unpinning to overcome the issue of fundamental contact resistance. Herein, an MIS contact structure with a 2-dimensional reduced graphene oxide (rGO) interlayer is proposed as an effective source/drain contact structure. The demonstration of a metal-rGO-semiconductor MIS (rGO MIS) contact structure with different interlayer thicknesses indicated that the rGO interlayer with a thickness of a few nanometers significantly enhanced the reverse current density (JR) by ∼2.0 × 103 times compared to that of the MS contact. In addition, the effective Schottky barrier height was reduced from 0.576 to 0.205 eV. This drastic improvement is attributed to the unique properties of rGO, such as its wide band gap, electrical conductivity, and Van der Waals interface leading to a metal-induced gap state reduction, tunneling resistance lowering, and passivation effect when it is adopted as an interlayer of the MIS contact. This result demonstrates the promising potential of using rGO as an MIS interlayer, which will pave the way toward high-performance emerging nanoelectronic devices.

Experimental and Modeling Study of Metal-Insulator Interfaces to Control the Electronic Transport in Single Nanowire Memristive Devices.

Memristive devices relying on redox-based resistive switching mechanisms represent promising candidates for the development of novel computing paradigms beyond von Neumann architecture. Recent advancements in understanding physicochemical phenomena underlying resistive switching have shed new light on the importance of an appropriate selection of material properties required to optimize the performance of devices. However, despite great attention has been devoted to unveiling the role of doping concentration, impurity type, adsorbed moisture, and catalytic activity at the interfaces, specific studies concerning the effect of the counter electrode in regulating the electronic flow in memristive cells are scarce. In this work, the influence of the metal-insulator Schottky interfaces in electrochemical metallization memory (ECM) memristive cell model systems based on single-crystalline ZnO nanowires (NWs) is investigated following a combined experimental and modeling approach. By comparing and simulating the electrical characteristics of single NW devices with different contact configurations and by considering Ag and Pt electrodes as representative of electrochemically active and inert electrodes, respectively, we highlight the importance of an appropriate choice of electrode materials by taking into account the Schottky barrier height and interface chemistry at the metal-insulator interfaces. In particular, we show that a clever choice of metal-insulator interfaces allows to reshape the hysteretic conduction characteristics of the device and to increase the device performance by tuning its resistance window. These results obtained from single NW-based devices provide new insights into the selection criteria for materials and interfaces in connection with the design of advanced ECM cells.

Interfacial electronic characteristics and tunable contact types in novel silicene/Janus Ga2STe heterobilayers

Silicene-based van der Waals (vdWs) heterstructures are expected to design novel nanoelectronic devices due to their intriguing properties. Here, we construct novel silicene/Janus Ga2STe heterobilayers by vertically stacking silicene and Janus Ga2STe monolayer. Employing first-principles calculations, their interfacial electronic properties, Schottky barriers, and contact types are investigated systematically. The silicene/Janus Ga2STe heterobilayers are verified to be favorable energetically and stable dynamically. We also find that the graphene-like Dirac cone is well preserved in the silicene/Janus Ga2STe heterobilayer, suggesting a high carrier mobility. Depending on the stacking orders, an n-type or a p-type Schottky contact can be acquired at the silicene/Janus Ga2STe interface. More importantly, vertical strain and electric field can effectively tune the interfacial electronic properties and contact type in the silicene/Janus Ga2STe heterobilayer. These findings can provide a useful guidance for designing controllable Schottky nanoelectronic devices based on silicene/Janus Ga2STe heterobilayers with high electronic performance.

Ferroelectricity and Piezoelectricity in 2D Van der Waals CuInP2S6 Ferroelectric Tunnel Junctions.

CuInP2S6 (CIPS) is a novel two-dimensional (2D) van der Waals (vdW) ferroelectric layered material with a Curie temperature of TC~315 K, making it promising for great potential applications in electronic and photoelectric devices. Herein, the ferroelectric and electric properties of CIPS at different thicknesses are carefully evaluated by scanning probe microscopy techniques. Some defects in some local regions due to Cu deficiency lead to a CuInP2S6–In4/3P2S6 (CIPS–IPS) paraelectric phase coexisting with the CIPS ferroelectric phase. An electrochemical strain microscopy (ESM) study reveals that the relaxation times corresponding to the Cu ions and the IPS ionospheres are not the same, with a significant difference in their response to DC voltage, related to the rectification effect of the ferroelectric tunnel junction (FTJ). The electric properties of the FTJ indicate Cu+ ion migration and propose that the current flow and device performance are dynamically controlled by an interfacial Schottky barrier. The addition of the ferroelectricity of CIPS opens up applications in memories and sensors, actuators, and even spin-orbit devices based on 2D vdW heterostructures.

Enhancing high-temperature capacitor performance of polymer nanocomposites by adjusting the energy level structure in the micro-/meso-scopic interface region

The interface plays a major role in the conduction and breakdown behaviors of dielectric materials. Enhancing interface compatibility and Schottky barrier to reduce conduction loss and enhance breakdown strength of nanocomposites has been widely studied. Nevertheless, there are few reports on the effect of the energy level structure in filler/polymer and electrode/dielectric interface region on the breakdown strength and high-temperature energy storage performances. Herein, the polyimide (PI) films sandwiched by Al2O3 layers and filled with SiO2 shell-coated high-K BaTiO3 nanofibers were prepared. Our results reveal that the wide bandgap oxide layer can regulate the energy level structure of the interface region, introduce deep traps in the nanocomposites and increase the Schottky barrier at the electrode/dielectric interface to impede charge injection and transport. Moreover, the nanocomposites combine the advantages of anisotropic dielectric properties from the Al2O3 layer, SiO2 shell, and BaTiO3 core, enhancing dielectric constants of the nanocomposites. The optimal nanocomposites show greatly enhanced discharge energy density and breakdown strength at 150 °C, which are 370% and 38% higher than those of PI, respectively. This work provides more insight into the mechanism of electrical conduction and breakdown in polymer nanocomposites and offers an effective strategy for developing polymer nanocomposites with superior capacitive performance at elevated temperatures.

Manipulation of current rectification in van der Waals ferroionic CuInP2S6

Developing a single-phase self-rectifying memristor with the continuously tunable feature is structurally desirable and functionally adaptive to dynamic environmental stimuli variations, which is the pursuit of further smart memristors and neuromorphic computing. Herein, we report a van der Waals ferroelectric CuInP2S6 as a single memristor with superior continuous modulation of current and self-rectifying to different bias stimuli (sweeping speed, direction, amplitude, etc.) and external mechanical load. The synergetic contribution of controllable Cu+ ions migration and interfacial Schottky barrier is proposed to dynamically control the current flow and device performance. These outstanding sensitive features make this material possible for being superior candidate for future smart memristors with bidirectional operation mode and strong recognition to input faults and variations.

Photovoltaic sensing of a memristor based in LSMO/BTO/ITO ferroionic tunnel junctions

Memristors based on oxide tunnel junctions are promising candidates for energy efficient neuromorphic computing. However, the low power sensing of the nonvolatile resistive state is an important challenge. We report the optically induced sensing of the resistive state of a memristor based on a La0.7Sr0.3MnO3/BaTiO3/In2O3:SnO2 (90:10) heterostructure with a 3 nm thick BaTiO3 ferroelectric barrier. The nonvolatile memristive response originates from the modulation of an interfacial Schottky barrier at the La0.7Sr0.3MnO3/BaTiO3 interface, yielding robust intermediate memristive states. The Schottky barrier produces a photovoltaic response when illuminated with a 3.3 eV UV LED, which depends on the state. The open circuit voltage Voc correlates linearly with the resistance of each state, enabling active sensing of the memristive state at light power densities as low as 20 mW/cm2 and temperatures up to 100 K. This opens up avenues for the efficient and minimally invasive readout of the memory states in hybrid devices.

Regulating interface Schottky barriers toward a high-performance self-powered imaging photodetector.

Two-dimensional (2D) layered organic–inorganic hybrid perovskites have attracted wide attention in high-performance optoelectronic applications due to their good stability and excellent optoelectronic properties. Here, a high-performance self-powered photodetector is realized based on an asymmetrical metal–semiconductor–metal (MSM) device structure (Pt-(PEA)2PbI4 SC-Ag), which introduces a strong built-in electric field by regulating interface Schottky barriers. Benefitting from excellent built-in electrical potential, the photodetector shows attractive photovoltaic properties without any power supply, including high photo-responsivity (114.07 mA W−1), fast response time (1.2 μs/582 μs) and high detectivity (4.56 × 1012 Jones). Furthermore, it exhibits high-fidelity imaging capability at zero bias voltage. In addition, the photodetectors show excellent stability by maintaining 99.4% of the initial responsivity in air after 84 days. This work enables a significant advance in perovskite SC photodetectors for developing stable and high-performance devices.

Regulating Interface Schottky Barriers Towar High-Performance Self-Powered Imaging Photodetector

Regulating Interface Schottky Barriers Towar High-Performance Self-Powered Imaging Photodetector

Characterization of Electrical Parameters of Copper Phthalocyanine Based Organic Electronic Device in Presence of Fullerene Nanoparticles

Characterization of electrical parameters of Copper Phthalocyanine dye has been done in the present work. In the context of electrical parameters, the Schottky barrier and ideality factor of the organic device has been measured and the effects of fullerene nanoparticles on these parameters have been studied. Analysis of electrical parameters has been done by the current-voltage characteristics of the device. The influence of fullerene nanoparticles lessens the Schottky barrier to 0.71 eV from 0.75 eV. The current flow is assumed to be injection limited as the Schottky barrier is greater than 0.3 eV - 0.4 eV. The Schottky barrier is also estimated by the Norde method. Norde's method shows lessening of barrier height from 0.70 eV to 0.65 eV under the influence of fullerene nanoparticles. The measured ideality factor value reduces from 3.787 to 1.495 in presence of fullerene nanoparticles. The charge injection mechanism at metal-organic contact gets influenced by the interfacial Schottky barrier height. Decrease in both Schottky barrier and ideality factor attribute to the increase in charge flow and it allows a reduction in the device’s transition voltage from 2.5 V to 1.0 V.

MoTe2 Field-Effect Transistors with Low Contact Resistance through Phase Tuning by Laser Irradiation.

Due to their extraordinary electrical and physical properties, two-dimensional (2D) transition metal dichalcogenides (TMDs) are considered promising for use in next-generation electrical devices. However, the application of TMD-based devices is limited because of the Schottky barrier interface resulting from the absence of dangling bonds on the TMDs’ surface. Here, we introduce a facile phase-tuning approach for forming a homogenous interface between semiconducting hexagonal (2H) and semi-metallic monoclinic (1T′) molybdenum ditelluride (MoTe2). The formation of ohmic contacts increases the charge carrier mobility of MoTe2 field-effect transistor devices to 16.1 cm2 V−1s−1 with high reproducibility, while maintaining a high on/off current ratio by efficiently improving charge injection at the interface. The proposed method enables a simple fabrication process, local patterning, and large-area scaling for the creation of high-performance 2D electronic devices.

Synthesis of nickel nanoparticles-deposited strontium titanate nanocubes (Ni-STO) and heterojunction electrical applications over a wide temperature range

In the present study, the structural properties of nickel nanoparticles-deposited strontium titanate nanocubes (Ni-STO) were examined by taking XRD, ICP-MS, TEM and SEM images. Temperature-dependent capacitance–voltage (C-V) and current–voltage (I-V) measurements were made for the electrical characterization of the Ni/Ni-STO/n-Si heterojunction devices produced. As the temperature increases from 80 K to 400 K, the ideality factor (n) decreases from 2.30 to 1.02 while barrier height (BH) increases from 0.27 eV to 0.80 eV. In the heterojunction device between Ni-STO and n-type Si, electrons can be captured at the Schottky barrier interface and recombinations can be reduced. Devices produced with Ni-STO material had a positive effect on performance compared to the devices produced with STO in previous studies. The electrical parameters obtained give compatible results as a function of temperature. Metal deposited STOs are potential candidates for temperature-dependent sensors and electrical devices.