Low Schottky Barrier Research Articles

Unraveling the Role of Interfacial Interactions in Electrical Contacts of Atomically Thin Transition-Metal Dichalcogenides.

Van der Waals (vdW) contact has been widely regarded as one of the most potential strategies for exploiting low-resistance metal-semiconductor junctions (MSJs) based on atomically thin transition-metal dichalcogenides (TMDs), but this method is still not efficient due to weak metal-TMD interfacial interactions. Therefore, an understanding of interfacial interactions between metals and TMDs is essential for achieving low-resistance contacts with weak Fermi level pinning (FLP). Herein, we report how the interfacial interactions between metals and TMDs affect the electrical contacts by considering more than 90 MSJs consisting of a semiconducting TMD channel and different types of metal electrodes, including bulk metals, MXenes, and metallic TMDs. We reveal that the vdW contact scheme cannot ensure the formation of low-resistance metal-TMD contacts. The interfacial coupling between metals and TMDs leads to a delicate competition between the FLP and carrier tunneling efficiency, which explains the broad experimental observations in which the weakly coupled van der Waals contacts usually show high contact resistance, while the strongly coupled metal-TMD contacts suffer from strong FLP. Benefiting from the low Schottky barrier and weak FLP, bulk Ag is a promising electrode for n-type MoS2 devices with a contact resistance of 83 Ω μm at a carrier concentration of 5.95 × 1013 cm-2, and 1T'-phase MoS2 and Sc2NO2 are identified as superior contact electrodes for p-type WSe2 devices. This work offers a general rule to exploit high-performance MSJs and clarifies the key role of interfacial coupling in the electrical contacts of TMD-based devices.

Pick-and-Place Transfer of Arbitrary-Metal Electrodes for van der Waals Device Fabrication.

Van der Waals electrode integration is a promising strategy to create nearly perfect interfaces between metals and 2D materials, with advantages such as eliminating Fermi-level pinning and reducing contact resistance. However, the lack of a simple, generalizable pick-and-place transfer technology has greatly hampered the wide use of this technique. We demonstrate the pick-and-place transfer of prefabricated electrodes from reusable polished hydrogenated diamond substrates without the use of any sacrificial layers due to the inherent low-energy and dangling-bond-free nature of the hydrogenated diamond surface. The technique enables transfer of arbitrary-metal electrodes and an electrode array, as demonstrated by successful transfer of eight different elemental metals with work functions ranging from 4.22 to 5.65 eV. We also demonstrate the electrode array transfer for large-scale device fabrication. The mechanical transfer of metal electrodes from diamond to van der Waals materials creates atomically smooth interfaces with no interstitial impurities or disorder, as observed with cross-section high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. As a demonstration of its device application, we use the diamond transfer technique to create metal contacts to monolayer transition metal dichalcogenide semiconductors with high-work-function Pd, low-work-function Ti, and semimetal Bi to create n- and p-type field-effect transistors with low Schottky barrier heights. We also extend this technology to air-sensitive materials (trilayer 1T' WTe2) and other applications such as ambipolar transistors, Schottky diodes, and optoelectronics. This highly reliable and reproducible technology paves the way for new device architectures and high-performance devices.

Enhanced UV–Vis Rejection Ratio in Metal/BaTiO3/β‐Ga2O3 Solar‐Blind Photodetectors

AbstractThe fabrication and characterization of metal/BaTiO3/β‐Ga2O3 solar‐blind photodetectors are reported. β‐Ga2O3 is a promising material for solar‐blind photodetectors due to its large bandgap and the availability of low defect‐density melt‐grown substrates. In this work, structures are introduced that employ high‐permittivity dielectric/semiconductor heterojunctions to enhance the performance of a Schottky photodetector. It is shown that integrating the high‐k dielectric BaTiO3 reduces the dark current by ≈104, all but eliminates illumination induced Schottky barrier lowering, and increases the UV–vis rejection ratio by a factor greater than 9 × 103 compared to a Schottky photodetector. It is hypothesized that the high permittivity of the dielectric overcomes the influence of self‐trapped holes in Ga2O3 to reduce the peak electric field at the dielectric/metal interface, thereby eliminating the effects of Schottky barrier lowering on illuminated β‐Ga2O3 photodetectors. Additionally, it is hypothesized that the increase in the UV–vis rejection ratio is caused by the “dead layer” that forms at the BaTiO3/Pt interface.

Contact Resistance Reduction of MoS2-Based Field Effect Transistor Using Semimetallic TiS2 Contact Layer Deposited By Atomic Layer Deposition

Recently, two-dimensional transition metal dichalcogenides (2D TMDCs) have been researched as promising channel materials for filed effect transistors (FETs) owing to their high mobility at atomic-level thickness. As miniaturization and high performance of the electronic devices are required, however, high contact resistance at the interface between the metal electrode and 2D TMDC channel has become a major challenge.1 The high contact resistance at the metal-semiconductor interface originates from the uncontrollable high Schottky barrier height (SBH). Due to Fermi-level pinning induced by metal-induced gap state (MIGS) and defect-induced gap state (DIGS), the barrier height cannot be controlled by conventional Schottky-Mott rule, regardless of metal work function. Since MIGS occurs due to perturbation of metal wave function into the semiconductor, inserting semimetallic material as contact layer can be a solution to suppress the MIGS and further reduce the contact resistance.2 In this study, ALD TiS2 was used as semimetallic contact layer between the MoS2 channel and Ti/Au electrode for MoS2-based TFT. With the TiS2 contact layer, we could observe improvements in overall device performances, which is attributed to the semimetallic nature of TiS2. In addition, low temperature ALD TiS2 process contributed to the clean interface with vdW bonding between MoS2 and TiS2, resulting in suppression of DIGS, as well as MIGS. Owing to the ALD TiS2 contact, we could mitigate FLP and achieve metal-semiconductor interface with low Schottky barrier height, resulting in low contact resistance. References 1 K. Schauble et al., “Uncovering the effects of metal contacts on monolayer MoS2,” ACS Nano, vol. 14, no. 11, pp. 14798–14808, 2020, doi: 10.1021/acsnano.0c03515. 2 P. C. Shen et al., “Ultralow contact resistance between semimetal and monolayer semiconductors,” Nature, vol. 593, no. 7858, pp. 211–217, 2021, doi: 10.1038/s41586-021-03472-9.

Exploration of High‐Pressure Annealing and Microwave Annealing in Palladium Germano‐Silicide Formation for Si0.8Ge0.2‐Based Complementary Metal‐Oxide–Semiconductor Transistors

In this study, forming palladium germano‐silicide on Si0.8Ge0.2‐based complementary metal‐oxide semiconductor (CMOS) transistors by high‐pressure annealing compared to microwave annealing is investigated. Boron‐doped Si0.8Ge0.2 layers are epitaxially grown on n‐type Si wafers, achieving an initial boron concentration of 5 × 1015 cm−3, which increase to ≈6 × 1020 cm−3 after microwave annealing, reducing sheet resistance. Palladium is deposited using electron beam evaporation to form a 15 nm layer on Si0.8Ge0.2 (200 nm)/Si (100) substrates. High‐pressure annealing is conducted from 300 to 500 °C in N2 ambiance at 5 kg cm−3, while microwave annealing is performed at 5.8 GHz and 1800–3000 W for 100 s. X‐ray diffractometer confirms high‐intensity Pd2Si phase formation, but scanning electron microscope and atomic force microscope reveal increased surface roughness and clustering after annealing. Sheet resistance increases from 10.35 Ω sq−1 (unannealed) to 131.8 Ω sq−1 (high‐pressure annealing at 300 °C) and 85.8 Ω sq−1 (microwave annealing at 1800 W). In these results, the trade‐offs between annealing methods and metal choices for achieving low contact resistance and Schottky barrier heights in p‐type Si0.8Ge0.2 CMOS circuits are highlighted.

Numerical analysis of Gaussian potential patches model depending on the substrate doping in inhomogeneous Schottky barrier diodes over a wide temperature range

The current-voltage (I-V-T) characteristics of an inhomogeneous n-type GaAs Schottky barrier diode have been investigated by numerical analysis using the modified thermionic emission (TE) current equation by Tung in the 40–320 K range at 40 K intervals. This total current (TC) equation consists of TE current and the patch current components. The patch current dominates through the low Schottky barrier height patches at low temperatures. From the I-V-T characteristics given for three different standard deviations (σ) at each substrate doping value Nd, we have determined the temperatures at which the patch current begins to dominate. The starting temperature of the patch current has decreased as the σ and Nd values decrease. It has been seen that the temperature at which the patch current component begins to dominate is about 120, 80, and 60 K for σ4, σ3, and σ2 at Nd=1.0×1014cm−3 or Nd=1.0×1015cm−3, respectively; 160, 120, and 80 K at Nd=5.0×1015cm−3; and 200, 160, and 80 K at Nd=1.0×1016cm−3, respectively. Moreover, for the substrate with high doping, it has been observed that the I-V curve of the patch current component or the TC shifts toward higher voltages than the expected position at low temperatures. Thus, from the I-V-T characteristics, it has appeared that Tung’s pinch-off model tends to be more applicable to lightly doped semiconductors. Moreover, the TC equation should be used at high temperatures because the I-V curves at high temperatures belong to the TE component, and the patch current expression without the TE component should be especially used for fit to the experimental curves at low temperatures.

Electrical contact property and control effects for stable T(H)-TaS2/C3B metal-semiconductor heterojunctions.

Metal-semiconductor heterojunctions are the basis for developing new electronic devices. Here, T(H)-TaS2/C3B metal-semiconductor heterostructures are constructed by different phase T- and H-TaS2 monolayers combined with the C3B monolayer. The calculated corrected binding energies, phonon band structures, elastic constants, and molecular dynamics simulations indicated that both heterojunctions are highly stable, meaning that T(H)-TaS2/C3B heterojunctions possibly exist in experiments. The electronic property calculations showed that the intrinsic T(H)-TaS2/C3B heterojunction is an n(p)-type Schottky contact with a low Schottky barrier height (SBH), which is very important for the design of high-performance field-effect transistors. The electronic properties of the T(H)-TaS2/C3B heterojunctions can be controlled by varying the vertical strain and external electric field; however, the strain only resulted in a small change in the heterojunction SBH. Nevertheless, under external electrical field control, the T-TaS2/C3B heterojunction could manage a transition from an n-type Schottky contact to an n-type Ohmic contact and the H-TaS2/C3B heterojunction could be altered from a p-type Schottky contact to a p-type Ohmic contact. These findings provide theoretical insights into the electronic and electrical contact properties of the T(H)-TaS2/C3B heterojunction, which could be beneficial for developing n-type MOS and p-type MOS transistors.

Low-Defect-Density Monolayer MoS2 Wafer by Oxygen-Assisted Growth-Repair Strategy.

Atomic chalcogen vacancy is the most commonly observed defect category in two dimensional (2D) transition-metal dichalcogenides, which can be detrimental to the intrinsic properties and device performance. Here a low-defect density, high-uniform, wafer-scale single crystal epitaxial technology by in situ oxygen-incorporated "growth-repair" strategy is reported. For the first time, the oxygen-repairing efficiency on MoS2 monolayers at atomic scale is quantitatively evaluated. The sulfur defect density is greatly reduced from (2.71 ± 0.65) × 1013 down to (4.28 ± 0.27) × 1012 cm-2, which is one order of magnitude lower than reported as-grown MoS2. Such prominent defect deduction is owing to the kinetically more favorable configuration of oxygen substitution and an increase in sulfur vacancy formation energy around oxygen-incorporated sites by the first-principle calculations. Furthermore, the sulfur vacancies induced donor defect states is largely eliminated confirmed by quenched defect-related emission. The devices exhibit improved carrier mobility by more than three times up to 65.2 cm2 V-1 s-1 and lower Schottky barrier height reduced by half (less than 20 meV), originating from the suppressed Fermi-level pinning effect from disorder-induced gap state. The work provides aneffective route toward engineering the intrinsic defect density and electronic states through modulating synthesis kinetics of 2D materials.

Study on the interface electronic structure, strain modulation and transport properties of composite heterojunction of 2D semimetal TiS2 and MX2 (M=Mo, W, Cr, Zr, Hf; X=S, Se, Te) semiconductor

Ohmic contacts play a crucial role in realizing high-performance electronic devices based on two-dimensional materials. The contact between semimetals and semiconductors can mitigate the formation of metal-induced gap states (MIGS), thereby reducing the SBH, enhancing the efficiency of high charge injection, and facilitating the establishment of ohmic contacts. This study involves a systematic exploration of the contact characteristics between the two-dimensional semimetal TiS2 and semiconductor MX2 (M = Mo, W, Cr, Zr, Hf; X = S, Se, Te) through first-principles calculations. It is found that the TiS2/MoSe2 and TiS2/WSe2 heterojunction achieve ohmic contact. Investigations into their transport properties reveal that significant currents can be observed at relatively low voltages, indicating excellent transport performance of these heterojunctions. The TiS2/CrSe2 and TiS2/HfSe2 contact heterojunctions also show low Schottky barrier height (SBH), with the barrier height being adjustable under strain. The SBH of TiS2/CrSe2 and TiS2/HfSe2 heterojunctions are very close to zero under stresses of 4 % and −4%, respectively. This also implies that our research can offer valuable guidance for the development of adjustable Schottky nano-devices and high-performance optoelectronic devices.

Compositional engineering of interfacial charge transfer in van der Waals heterostructures of graphene and transition metal dichalcogenides.

Owing to their unique optical and electronic properties, vertical van der Waals heterostructures (vdWHs) have attracted considerable attention in optoelectronic applications, such as photodetection, light harvesting, and light-emitting diodes. To fully harness these properties, it is crucial to understand the interfacial charge transfer (CT) and recombination dynamics across vdWHs. However, the effects of interfacial energetics and defect states on interfacial CT and recombination processes in graphene-transition metal dichalcogenide (Gr-TMD) vdWHs remain debated. Here, we investigate the interfacial CT dynamics in Gr-TMD vdWHs with different chemical compositions (W, Mo, S, and Se) and tunable interfacial energetics. We demonstrate, using ultrafast terahertz spectroscopy, that while the photo-induced electron transfer direction is universal with graphene donating electrons to TMDs, its efficiency is chalcogen-dependent: the CT efficiency of S atom-based vdWHs is 3-5 times higher than that of Se-based vdWHs thanks to the lower Schottky barrier present in S-based vdWHs. In contrast, the electron back transfer process from TMD to Gr, which defines the charge separation time, is transition metal-dependent and dominated by the mid-gap defect level of TMDs: W transition metal-based vdWHs possess extremely long charge separation, well beyond 1ns, which is significantly longer than Mo-based vdWHs with only 10s of ps charge separation. This difference can be traced to the much deeper mid-gap defect reported in W-based TMDs compared to Mo-based ones, resulting in modified energetics for the back electron transfer from the trapped states to graphene. Our results shed light on the role of interfacial energetics and defects by tailoring chemical compositions of TMDs on the interfacial CT and recombination dynamics in Gr-TMD vdWHs, which is pivotal for optimizing optoelectronic devices, particularly in the field of photodetection.

Janus MoSH/WSi2N4 van der Waals Heterostructure: Two-Dimensional Metal/Semiconductor Contact.

Constructing heterostructures from already synthesized two-dimensional materials is of significant importance. We performed a first-principles study to investigate the electronic properties and interfacial characteristics of Janus MoSH/WSi2N4 van der Waals heterostructure (vdWH) contacts. We demonstrate that the p-type Schottky formed by MoSH/WSi2N4 and MoHS/WSi2N4 has extremely low Schottky barrier heights (SBHs). Due to its excellent charge injection efficiency, Janus MoSH may be regarded as an effective metal contact for WSi2N4 semiconductors. Furthermore, the interfacial characteristics and electronic structure of Janus MoSH/WSi2N4 vdWHs can not only reduce/eliminate SBH, but also forms the transition from p-ShC to n-ShC type and from Schottky contact (ShC) to Ohmic contact (OhC) through the layer spacing and electric field. Our results can offer a fresh method for optoelectronic applications based on metal/semiconductor Janus MoSH/WSi2N4 vdW heterostructures, which have strong potential in optoelectronic applications.

Constrained patterning of orientated metal chalcogenide nanowires and their growth mechanism

One-dimensional metallic transition-metal chalcogenide nanowires (TMC-NWs) hold promise for interconnecting devices built on two-dimensional (2D) transition-metal dichalcogenides, but only isotropic growth has so far been demonstrated. Here we show the direct patterning of highly oriented Mo6Te6 NWs in 2D molybdenum ditelluride (MoTe2) using graphite as confined encapsulation layers under external stimuli. The atomic structural transition is studied through in-situ electrical biasing the fabricated heterostructure in a scanning transmission electron microscope. Atomic resolution high-angle annular dark-field STEM images reveal that the conversion of Mo6Te6 NWs from MoTe2 occurs only along specific directions. Combined with first-principles calculations, we attribute the oriented growth to the local Joule-heating induced by electrical bias near the interface of the graphite-MoTe2 heterostructure and the confinement effect generated by graphite. Using the same strategy, we fabricate oriented NWs confined in graphite as lateral contact electrodes in the 2H-MoTe2 FET, achieving a low Schottky barrier of 11.5 meV, and low contact resistance of 43.7 Ω µm at the metal-NW interface. Our work introduces possible approaches to fabricate oriented NWs for interconnections in flexible 2D nanoelectronics through direct metal phase patterning.

Evidence of contact-induced variability in industrially-fabricated highly-scaled MoS2 FETs

Evidence of microscopic inhomogeneities of the side source/drain contacts in 300 mm wafer integrated MoS2 field-effect transistors is presented. In particular, the presence of a limited number of low Schottky barrier spots through which channel carriers are predominantly injected is demonstrated by the dramatic current changes induced by individual charge traps located near the source contact. Two distinct types of “contact-impacting traps” are identified. Type-1 trap is adjacent to the contact interface and exchanges carriers with the metal. Its impact is only observable when the adjacent contact is the reverse-biased FET source and limits the channel current. Type-2 trap is located in the AlOx gate oxide interlayer, near the source contact, and exchanges carriers with the channel. Its capture/emission time constants exhibit both a gate and drain bias dependence due to the high sensitivity of the contact regions to the applied lateral and vertical fields. Unlike typical channel-impacting oxide traps, both types of reported defects affect the Schottky barrier height and width rather than the threshold voltage and result in giant random telegraph noise (RTN). These observations indicate that the contact quality and geometry play a fundamental role in the ultimate scaling of 2D FETs.

Interface Characterization of Graphene‐Silicon Heterojunction Using Hg Probe Capacitance–Voltage Measurement

AbstractInvestigating the intrinsic properties of the Schottky interface between graphene and 3D bulk silicon is crucial. However, the semiconductor technology introduces extra doping and defects in graphene, which significantly disturbs the property of the graphene‐silicon interface. Here, the interface parameters of graphene/n‐Si heterojunction are derived by the damage‐free Hg‐probe capacitance–voltage measurement. Due to its low‐density states, the Fermi level of graphene can be pushed upward, which results in a lower Schottky barrier height (ΦB0) of Hg/graphene/n‐Si (HGS) heterostructure than that of Hg/n‐Si (HS) structure. Additionally, the series resistance (Rs) of HGS becomes lower than that of HS, which can be attributed to the narrowed depletion layer width (WD) and the decreased interface state density (Nit). Furthermore, the frequency characteristic is also investigated. Because of the weak interface state charge trapping–detrapping process and the decreased Nit at high frequency, electrons will accumulate in graphene, and the Fermi level will be pushed up. Hence, the ΦB0 and Rs will decrease with increasing frequency. This study contributes to a deep understanding of the graphene/silicon heterojunction interfaces, which is crucial for designing and optimizing the new electronic and optoelectronic devices based on 2D/3D heterostructure.

Modulate the work function of MXene in MXene/InGaN heterojunction for visible light photodetector

MXene/InGaN heterojunction photodetectors with simple structure and superior optoelectronic performance are considered a viable option for optical communication. However, the integration of MXene with InGaN faces the problem of a relatively low Schottky barrier, leading to electron backflow, which hinders the separation of carriers and limits the photoresponse of photodetectors. Herein, high-performance MXene/InGaN heterojunction photodetectors were fabricated, and the work function of Ti3C2TX was modulated to explore its effect on the performance of the photodetectors. The ascorbic acid treatment increased the work function of MXene from 4.20 to 4.34 eV, enhancing the Schottky barrier height of the heterojunction from 0.56 to 0.70 eV. The devices exhibit excellent photoresponse performances, such as a responsivity of 0.133 A W−1 and a specific detectivity of 2.81 × 1011 Jones at −1 V bias, as well as a short rise/decay time of 37.49/110 μs at 0 V bias. Additionally, the photodetectors achieve high stability that can maintain over 95% of the initial value after 3 months. This work indicates the potential for utilizing tunable MXene work function to construct high-performance optoelectronic devices for visible light applications.

Comparative Analysis of Ni/Ag and Ni/Au Contacts on GaN/AlGaN/GaN Platform

Herein, the electrical characteristics and Schottky barrier of Ni/Au and Ni/Ag contacts on the GaN/AlGaN/GaN heterojunction are investigated. Both contacts on the p‐GaN contact layer (Mg: ≈3 × 1019 cm−3) exhibit weak Schottky characteristics. The nonlinear current–voltage (I–V) characteristics are observed, leading to variations in contact resistance (RC) and sheet resistance (Rsh) with changing bias voltage. The Ni/Ag contact achieves a lower Schottky barrier height calculated by using the I–V method. Furthermore, when employing a p++‐GaN layer (Mg: ≈1 × 1020 cm−3) as the contact layer, the Ni/Ag contact forms an Ohmic contact without Schottky characteristics, achieving a satisfactory RC of 30.31 Ω mm. This result demonstrates its viability as a competitive candidate for p‐channel field‐effect transistors’ fabrication.

High breakdown voltage of 1.3 kV and low turn-on voltage of 0.48 V β-Ga2O3 heterojunction barrier Schottky diode with tungsten Schottky contact

β-Ga2O3 power diodes were expected to possess low turn-on voltage (V on), low reverse leakage (J R), and high blocking capability for low power losses. In this work, a low V on (0.48 V) β-Ga2O3 heterojunction barrier Schottky diode (HJBS) with tungsten Schottky contact was achieved. Benefitting from the lateral depletion of p+-NiO to suppress J R originating from the low Schottky barrier, the blocking capability of β-Ga2O3 HJBS was enhanced. The spacing width of p+-NiO was systematically studied to reveal its modulation effect on forward and reverse characteristics. This work provides a promising strategy for improving rectifier efficiency of β-Ga2O3 diodes.

Impact of Rh, Ru, and Pd Leads and Contact Topologies on Performance of WSe2 FETs: A First Comparative Ab Initio Study.

2D field-effect transistors (FETs) fabricated with transition metal dichalcogenide (TMD) materials are a potential replacement for the silicon-based CMOS. However, the lack of advancement in p-type contact is also a key factor hindering TMD-based CMOS applications. The less investigated path towards improving electrical characteristics based on contact geometries with low contact resistance (RC) has also been established. Moreover, finding contact metals to reduce the RC is indeed one of the significant challenges in achieving the above goal. Our research provides the first comparative analysis of the three contact configurations for a WSe2 monolayer with different noble metals (Rh, Ru, and Pd) by employing ab initio density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. From the perspective of the contact topologies, the RC and minimum subthreshold slope (SSMIN) of all the conventional edge contacts are outperformed by the novel non-van der Waals (vdW) sandwich contacts. These non-vdW sandwich contacts reveal that their RC values are below 50 Ω∙μm, attributed to the narrow Schottky barrier widths (SBWs) and low Schottky barrier heights (SBHs). Not only are the RC values dramatically reduced by such novel contacts, but the SSMIN values are lower than 68 mV/dec. The new proposal offers the lowest RC and SSMIN, irrespective of the contact metals. Further considering the metal leads, the WSe2/Rh FETs based on the non-vdW sandwich contacts show a meager RC value of 33 Ω∙μm and an exceptional SSMIN of 63 mV/dec. The two calculated results present the smallest-ever values reported in our study, indicating that the non-vdW sandwich contacts with Rh leads can attain the best-case scenario. In contrast, the symmetric convex edge contacts with Pd leads cause the worst-case degradation, yielding an RC value of 213 Ω∙μm and an SSMIN value of 95 mV/dec. While all the WSe2/Ru FETs exhibit medium performances, the minimal shift in the transfer curves is interestingly advantageous to the circuit operation. Conclusively, the low-RC performances and the desirable SSMIN values are a combination of the contact geometries and metal leads. This innovation, achieved through noble metal leads in conjunction with the novel contact configurations, paves the way for a TMD-based CMOS with ultra-low RC and rapid switching speeds.

Significant Enhancement of Electrocaloric Effect in Ferroelectric Polycrystalline Ceramics Through Grain Boundary Barrier Engineering

AbstractA key challenge currently for the new ferroelectric refrigeration with high efficiency and environmental friendliness lies in the urgent demand for ferroelectric materials with huge electrocaloric effects (ECE). Ferroelectric polycrystalline ceramics with high ECE stand out as one of the most promising candidates for electrocaloric cooling applications. However, the grain boundary network, as a barrier for the cross‐transmission of charged carriers, widely exists in electrocaloric polycrystalline ceramics and is often neglected in favor of focusing more on composition regulation and structural design. Herein, a grain boundary barrier engineering is proposed that regulates the Schottky barrier at the grain boundary network in the Ba0.8Zr0.2TiO3 ceramics by a maneuverable annealing process and clarifies its critical role in enhancing the ECE of polycrystalline ceramics. As a result, a substantial enhancement of the EC performance (from 0.68 to 1.63 K at 50 °C and 80 kV cm−1, ≈2.4 times) has been achieved in the annealed Ba0.8Zr0.2TiO3 ceramics with a lower Schottky barrier. The microstructural and electrical characterization reveals that the lower Schottky barrier in the grain boundary network facilitates the domain switching and electronic transition, hence resulting in enhanced polarization response and EC performance.

High-Performance Contact-Doped WSe2 Transistors Using TaSe2 Electrodes.

Two-dimensional (2D) transitional metal dichalcogenides (TMDs) have garnered significant attention due to their potential for next-generation electronics, which require device scaling. However, the performance of TMD-based field-effect transistors (FETs) is greatly limited by the contact resistance. This study develops an effective strategy to optimize the contact resistance of WSe2 FETs by combining contact doping and 2D metallic electrode materials. The contact regions were doped using a laser, and the metallic TaSe2 flakes were stacked on doped WSe2 as electrodes. Doping the contact areas decreases the depletion width, while introducing the TaSe2 contact results in a lower Schottky barrier. This method significantly improves the electrical performance of the WSe2 FETs. The doped WSe2/TaSe2 contact exhibits an ultralow Schottky barrier height of 65 meV and a contact resistance of 11 kΩ·μm, which is a 50-fold reduction compared to the conventional Cr/Au contact. Our method offers a way on fabricating high-performance 2D FETs.