Low Contact Resistance Research Articles

CNTs-TiB2/Cu laser cladding layer with enhanced tribo-electrical property on wind turbine pitch slip ring

Wind turbine pitch slip ring requires excellent tribo-electrical properties, including low friction and wear, high current transmission efficiency, low power loss and contact resistance. To improve the tribo-electrical property, a CNTs-TiB2/Cu coating was prepared on slip ring surface by laser cladding. Microstructure, dilution rate, microhardness, tribo-electrical property and power transmission property of cladding layer were analyzed. Optimal metallurgical bonding was achieved at a laser power of 900 W, resulting in a dilution rate of 14.5%. Elemental Ti diffused from the substrate into the coating, forming a hard TiC phase that significantly improved both friction reduction and wear resistance. Additionally, the formation of Cu3Ti increased the electrical conductivity of the cladding layer. The contact resistance was reduced by 30% to below 0.06 Ω, while the current transmission efficiency improved by 25%, exceeding 90%.

Record Low Contact Resistivity of 10-8 Ω cm² Ohmic Contacts on Oxygen-Terminated Intrinsic Diamond by Transition Metals Metallization

Record Low Contact Resistivity of 10^-8 Ω cm² Ohmic Contacts on Oxygen-Terminated Intrinsic Diamond by Transition Metals Metallization

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.

Low Contact Resistance WSe2 p-Type Transistors with Highly Stable, CMOS-Compatible Dopants.

High contact resistance has been a bottleneck in developing high-performance transition-metal dichalcogenide (TMD) based p-type transistors. We report degenerately doped few-layer WSe2 transistors with contact resistance as low as 0.23 ± 0.07 kΩ·μm per contact by using platinum(IV) chloride (PtCl4) as the p-type dopant, which is composed of ions compatible with the complementary metal-oxide-semiconductor (CMOS) fabrication process. Top-gated devices with a gate length of 200 nm showed good switching behaviors, implying that the dopant diffusion into the gate stack is not significant. The devices showed nearly identical performance after being kept in air for 86 days without any encapsulation while retaining the degenerately doped states at 78 K with pressure lower than 10-5 Torr, highlighting the stability of the dopants. The presented method sets forth the availability of highly stable methods for pattern doping the transistors with a thinned Schottky barrier width for low contact resistance devices.

Corrosion behavior of TiZrNbC coatings on TA1 substrates in simulated PEM water electrolysis

A TiZrNbC coating was deposited on the TA1 substrate by magnetron sputtering technology, and the corrosion behaviors of the TiZrNbC coating in a simulated proton exchange membrane water electrolysis (PEMWE) environment under fluctuating potentials were investigated. The microstructures and elemental distributions of the coating were characterized by SEM and EDS. The PEMWE environment was simulated using a dilute H2SO4 solution with pH = 3 and a 5 ppm of fluoride (F-) ions addition, and polarization tests were conducted under the potentials with constant, square and triangular waveforms. The corrosion resistances of the TiZrNbC-coated and bare TA1 substrates were characterized by potentiodynamic polarization, electrochemical impedance spectroscopy and interfacial contact resistance tests. Compared to the bare TA1 substrates, the TiZrNbC-coated TA1 substrates exhibited lower corrosion current densities, higher polarization resistances and lower contact resistances, demonstrating a superior corrosion resistance.

Understanding the Impact of Contact-Induced Strain on the Electrical Performance of Monolayer WS2 Transistors.

Two-dimensional (2D) electronics require low contact resistance (RC) to approach their fundamental limits. WS2 is a promising 2D semiconductor that is often paired with Ni contacts, but their operation is not well understood considering the nonideal alignment between the Ni work function and the WS2 conduction band. Here, we investigate the effects of contact size on nanoscale monolayer WS2 transistors and uncover that Ni contacts impart stress, which affects the WS2 device performance. The strain applied to the WS2 depends on contact size, where long (1 μm) contacts (RC ≈ 1.7 kΩ·μm) show a 78% reduction in RC compared to shorter (0.1 μm) contacts (RC ≈ 7.8 kΩ·μm). We also find that thermal annealing can relax the WS2 strain in long-contact devices, increasing RC to 8.5 kΩ·μm. These results reveal that thermo-mechanical phenomena can significantly influence 2D semiconductor-metal contacts, presenting opportunities to optimize device performance through nanofabrication and thermal budget.

Regulated charge transfer by cascade dual Z-scheme heterojunction of HCdS@ZnIn2S4-Cobalt porphyrin for efficient photocatalytic solar fuel production

Dual Z-schemed photocatalysts possess superior charge-separation efficiency and powerful redox capabilities, which have attracted significant attention in photocatalytic CO2 reduction (PCR). However, most of the dual Z-scheme systems are focused on inorganic semiconductors, which remain a challenge to control the selectivity of PCR products. Herein, we designed a cascade dual Z-scheme structured organic/inorganic heterojunction of HCdS@ZnIn2S4-Cobalt porphyrin (HCdS@ZIS-CoTPPS). HCdS@ZIS-CoTPPS demonstrated excellent PCR activity (CO rate: 93.64 μmol·g−1·h−1) and adjustable syngas ratio when compared to HCdS, ZIS, CoTPPS, and HCdS/ZIS. Experimental characterizations and density functional theory (DFT) calculations reveal that the superior PCR activity of HCdS@ZIS-CoTPPS is contributed by the broad light absorption range, short charge carrier migration path, low interface contact resistance, and strong redox ability induced by the hollow structured cascade dual Z-scheme heterojunction. This article provides valuable inspiration for the design and preparation of atomistic heterojunctions for solar-driven fuel generation.

Growth of Ta-doped SnO2 on GaN as a UV-transparent conducting electrode and band alignment properties of the heterojunction

GaN-based ultraviolet light emitting diodes (UV LEDs) have attracted considerable attention in recent years and are required in various applications such as healthcare, light illumination, and optical communication. However, the limited UV transparency of the electrodes like indium-doped tin oxide has hindered the external quantum efficiency of current UV LEDs. In this work, we present the growth of UV-transparent Ta-doped SnO2 (TTO) thin films on GaN as a promising UV-transparent electrode for LEDs. TTO thin films with a thickness of 200 nm exhibit optical transmission exceeding 80% at the wavelength of 300 nm, with a low resistivity of 2.5 × 10−4 Ω·cm and a low contact resistance of 1.7 × 10−2 Ω cm2 to n-type GaN. High-resolution x-ray photoemission spectra were employed to reveal insight into the electronic structure of TTO and the interfacial band alignment of TTO/GaN heterojunction. The wide optical bandgap (∼4.6 eV) and high UV transparency of TTO films stem from a significant Burstein–Moss shift due to degenerate doping, giving rise to metal-like characteristics and a small barrier height at the interface of TTO/GaN. These findings imply the origin of low contact resistivity of TTO to n-type GaN and may be applicable to the development of UV-transparent electrodes of optoelectronic devices.

Exploring low temperature-sputtered indium tin oxide (ITO) as an anti-reflection layer for silicon solar cells

Abstract This paper tackles challenges in silicon (Si) solar cells, specifically the use of hazardous Phosphorus Oxychloride (POCl3) for emitter formation and silane/ammonia for the Anti-Reflective Coating (ARC) layer, accompanied by high-temperature metallization. The study proposes an eco-friendly ARC layer process, replacing toxic materials. Indium Tin Oxide (ITO) with a refractive index of ∼2.0 is suggested as a non-toxic substitute for SiN x in the ARC layer. ITO enables fine-tuning of optical parameters and, with its electrical properties, supports low-resistivity contacts through efficient, low-temperature metallization processes. ITO-passivated solar cells with Ag polymer paste as a front contact exhibit promising characteristics: a commendable photocurrent density (J sc) of 20 mA cm−2 at 850 °C, low series resistance (R s) of 1.9 Ω, and high shunt resistance (R shunt) of 28.9 Ω, as demonstrated by illuminated I–V measurements. Implementing ITO as the ARC on a less toxic emitter junction enhances Si solar cells’ current density gain, minimizing current leakage during high-temperature processing. In conclusion, adopting less toxic materials and employing low-temperature processing in passive silicon solar cell fabrication presents an attractive alternative for cost reduction and contributes to environmentally sustainable practices in green manufacturing.

Unveiling Versatile Electronic Properties and Contact Features of Metal-Semiconductor Graphene/γ-Ge2SSe van der Waals Heterostructures.

Recently, searching for a metal-semiconductor junction (MSJ) that exhibits low-contact resistance has received tremendous consideration, as they are essential components in next-generation field-effect transistors. In this work, we design a MSJ by integrating two-dimensional (2D) graphene as the metallic electrode and 2D Janus γ-Ge2SSe as the semiconducting channel using first-principles simulations. All the graphene/γ-Ge2SSe MSJs are predicted to be energetically, mechanically, and thermodynamically stable, characterized by the weak van der Waals (vdW) interactions. The graphene/γ-SGe2Se MSJ-vdWH form the n-type Schottky contact (SC), while the graphene/γ-SeGe2S MSJ-vdWH form the p-type one, suggesting that the switching between p-type and n-type SC in the graphene/γ-Ge2SSe MSJ-vdWHs can occur spontaneously by simply altering the stacking patterns, without requiring any external conditions. Notably, the contact features, including contact types and barriers of the graphene/γ-Ge2SSe MSJs are significant in versatility and can be altered by applying electric gating and adjusting interlayer spacing. Both the applied electric gating and strain engineering induce switchability between p- and n-type and SC to OC in the graphene/γ-Ge2SSE MSJs. This versatility underscores the potential of the graphene/γ-Ge2SSe MSJ for next-generation applications that require low-contact resistance and high performance.

Boron‐Doped Zinc Oxide Electron‐Selective Contacts for Crystalline Silicon Solar Cells with Efficiency over 22.0%

The exploration of wide‐bandgap metal compound films with excellent passivation and contact properties on crystalline silicon (c‐Si) surface, as alternatives to traditional‐doped Si thin films, holds significant promise for the future enhancement of c‐Si solar cell efficiency. Herein, conductive boron‐doped zinc oxide (ZnO:B) films are deposited by atomic layer deposition (ALD) process and investigated as electron‐selective contacts, in combination with a thin SiOx passivating interlayer. This combination demonstrates a relative low contact resistivity of ≈2 mΩ cm2 and improved passivation quality. Further application of this SiOx/ZnO:B stack as a full‐area electron‐selective passivating contact in proof‐of‐concept n‐type c‐Si solar cells results in a satisfactory power conversion efficiency of over 22.0%. This electron‐selective passivating contact structure, prepared via low‐temperature, simplified, and the compositionally controlled ALD process, offers a promising pathway for the development of high‐efficiency and low‐cost c‐Si solar cells.

High-Performance p-Type Quasi-Ohmic of WSe2 Transistors Using Vanadium-Doped WSe2 as Intermediate Layer Contact.

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs), such as tungsten diselenide (WSe2), hold immense potential for applications in electronic and optoelectronic devices. However, a significant Schottky barrier height (SBH) at the metal-semiconductor (MS) interface reduces the electronic device performance. Here, we present a unique 2D/2D contact method for minimizing contact resistance and reducing the SBH. This approach utilizes vanadium-doped WSe2 (V-WSe2) as the drain and source contacts. The fabricated transistor exhibited a stable operation with p-type quasi-ohmic contact and a high on/off current ratio surpassing 108 at room temperature, reaching 1011 at 10 K. The device achieved an on-current of 68.87 μA, a high mobility of 103.80 cm2 V-1 s-1, a low contact resistance of 0.92 kΩ, and remarkably low SBH values of 1.51 meV for holes at VGS = -120 V with fixed VDS = 1 V. Furthermore, a Schottky photodiode has been fabricated, utilizing V-WSe2 and Cr as the asymmetric contact platform, showing a responsivity of 116 mA W1-. The findings of this study suggest a simple and efficient method for improving the performance of TMDC-based transistors.

Polymer hydrogel electronics with adhesive, self-healing, and anti-ultraviolet capabilities for machine learning-promoted electrophysiological detection

While adjustable mechanical properties, diverse biochemical features, and good ionic conductivity enabled by molecular engineering, polymer hydrogels as ionic skins (i-skins) are still limited by multiple challenges in the practical human health monitoring and health diagnosis, such as undesirable ductility and contact adhesion, poor functionality, and insufficient sensing ability. In view of this, the strategy of multiple dynamic interactions was proposed, and a mussel characteristic double-network polymer composite hydrogel (PG-BT2) with tannic acid and borax as dynamic media was reasonably designed. Due to the dynamic reversible interactions from the crosslinked network combined with special functional groups, the obtained PG-BT2 hydrogel attains remarkable stretchability with >1200 % elongation and good toughness of 268.6 kJ/m−3, and also possesses favorable versatility (e.g., self-healing time <2 s, adhesion strength of 4.62 kPa to pigskin, and UV transmittance of 15.3 % at 365 nm). Additionally, the i-skin derived from the PG-BT2 hydrogel exhibits excellent sensing properties, including a low interface contact resistance of 8.3 kΩ at 1 kHz, fast response/recovery time of 0.657 s/0.348 s, and a wide sensing range of 0–1100 % strain. By combining the hydrogel-based i-skin patch with the wireless circuit connected to a Bluetooth module, the constructed sensor system is capable of accurately monitoring micro-expressions and multi-joint movements. The portable system is also demonstrated to capture high-fidelity signals of electrocardiograms available for training artificial intelligence, achieving differentiation and recognition of blood pressure status, which will greatly benefit health management and intelligent medicine.

A novel dual functional gradient Zn(O,S)/Mg electron-selective contact for dopant‐free silicon solar cells with efficiencies approaching 21 %

Dopant-free carrier-selective contacts have the potential to mitigate or eliminate parasitic absorption, auger recombination losses, etc. Therefore, the vigorous development of dopant-free carrier-selective contact materials is an important way to enhance the performance of crystalline silicon (c-Si) photovoltaics. This study presents the concept of magnetron sputtering gradient deposited zinc oxide (Gd-Zn(O,S)) combined with a low work function magnesium metal layer. Subsequently, the Gd-Zn(O,S)/Mg bifunctional layer was further investigated and optimised to determine its suitability as a contact layer for electron transfer in c-Si solar cells. This strategy simultaneously enables a good passivation and a low contact resistance. The c-Si(n)/a-Si:H(i)/Gd-Zn(O,S)/Mg devices are constructed and achieved an optimal contact recombination current density (J0) of approximately 1.51 fA cm−2, along with a minimum ρc of approximately 35.89 mΩ.cm2. As a consequence, the power conversion efficiency of a prototype silicon heterojunction solar cell is 20.92 %. This study demonstrates that the strategy of replacing the a-Si:H(n) electron transport layer with Gd-Zn(O,S) is an effective approach for improving the SHJ cell. This study also provides new perspectives for designing novel dopant-free carrier-selective contact structures.

Role of electrostatic doping on the resistance of metal and two-dimensional materials edge contacts

In this theoretical study, we compare electrostatically doped metal-transition metal dichalcogenide (TMD) edge-contacts versus substitutionally doped edge-contacts in terms of their contact resistance. Our approach involves the utilization of electrostatic doping achieved by applying back-gate bias to the metal-TMD edge contacts, where carrier injection is primarily governed by the Schottky barrier at the interface. To analyze these contacts, we employ the Wentzel-Kramers-Brillouin (WKB) approximation to calculate the transmission coefficient and use density functional theory (DFT)-derived band structures. We numerically solve the Poisson equation to capture the electrostatic potential. We also account for the impact of the image force using Green's function for the Poisson equation with boundary conditions appropriate to our specific geometry. Our findings reveal that electrostatically doped TMD edge contacts exhibit higher contact resistance compared to impurity-doped edge contacts at equivalent carrier concentrations. At the same time, we find that, among the electrostatically doped edge contacts, a low-κ back-gate oxide in conjunction with low-κ top oxide is preferable in terms of improvement in contact resistance. For instance, in a metal-TMD edge contact scenario involving a monolayer MoS2 as the channel, SiO2 as the infinitely thick top oxide, and a SiO2 back-gate oxide with an equivalent oxide thickness (EOT) of 1nm, we demonstrate that it is possible to achieve an impressively low contact resistance of 50Ωµm when the back-gate bias exceeds or equals 2 V. Published by the American Physical Society 2024

2D Gr/WSe2/MoTe2 vertical heterojunction for self-powered photodiode with ultrafast response and high sensitivity

Two-dimensional materials without lattice constraints can be combined into form heterojunctions via van der Waals forces, providing opportunities for the future development of novel high-performance photodetectors. In non-vertical heterojunction devices with long carrier transport channels, SRH recombination due to defect and interface states in the heterojunction and Langevin recombination due to Coulomb interactions induce large amounts of photogenerated carrier recombination, leading to low quantum efficiencies of the heterojunction. At the same time, defect and interface trap states, as well as the long channel of the non-vertical heterojunction device, lead to a slow response speed of the device. In this work, a 2D WSe2/MoTe2 vertical heterojunction photodiode with a transparent graphene top electrode has been designed to simultaneously achieve high sensitivity and fast response speed of photodetectors. Benefiting from the vertical device structure, high-quality interface and low contact resistance, the photogenerated electron-hole pairs can be efficiently separated and transported. The photodiode exhibits remarkable rectification characteristics with a rectification ratio as high as 1.4 × 104, and provides a broadband and self-powered photodetection from the visible to NIR bands (405–1064 nm) with a maximum responsivity of 0.33 A/W at 785 nm. In particular, the photodiode achieves an ultra-fast rise/fall time of 6.49/6.22 μs at 0 V and a further reduction of the response time to 1.68/1.2 μs at a reverse bias of −1 V. This ultra-fast response allows the photodiode to detect switching signals with a cutoff frequency of more than 70 kHz and 200 kHz at 0 V and −1 V, respectively. This work opens up new opportunities for the development of integrated 2D photodetectors with low power consumption, high sensitivity, and high speed.

Au-free V/Al/Pt Contacts on n-Al0.85Ga0.15N:Si Surfaces of Far-UVC LEDs

The feasibility of replacing the V/Al/Ni/Au contact on n-Al0.85Ga0.15N:Si commonly used in far-UVC LEDs with a Au-free V/Al/Pt contact has been investigated. It is shown that the V and Pt layer thicknesses play an important role for achieving a low contact resistivity and a smooth contact surface at a low annealing temperature. The specific contact resistivity of V(10 nm)/Al(120 nm)/Pt(40 nm) annealed at 700 °C for 5 min is comparable with that of V(15 nm)/Al(120 nm)/Ni(20 nm)/Au(30 nm) annealed at 850 °C for 30 s. Furthermore, the root mean square roughness of the optimized V/Al/Pt contacts was 8.3 nm as compared to 30 nm for V/Al/Ni/Au.

Optimization of rear surface morphology in n-type TOPCon c-Si solar cells

Tunnel oxide passivated contact (TOPCon) crystalline silicon (c-Si) solar cells have attracted much attention because of their superior electrical properties such as the lower contact resistivity and better interface passivation at high temperatures. However, the TOPCon c-Si solar cells also have room for further improvement in optical performance, and the embodiment of optical advantages needs to be matched synchronously in electrical aspect. Here, the rear silicon pyramids with different angles have been achieved through solution corrosion to maximize the light absorption in the c-Si substrate. The light absorption for the pyramid angle of less than 30° is better. Compared with the cell samples with rear pyramid for a certain angle, the samples with flat back surface possess better surface passivation, and the contact resistivity can be reduced effectively by increasing the phosphorus doping concentration and adjusting the annealing temperature. Furthermore, the TOPCon c-Si solar cells with flat rear surface covered by 70 nm poly-Si have been demonstrated to increase the conversion efficiency by about 0.15 % vs. the counterpart for poly-Si of 130 nm thickness, and the improvement is mainly due to the increase of JSC and FF by 0.07 mA/cm2 and 0.72 %, respectively.

Enhanced adhesion strength of copper metallization on silicon heterojunction solar cell due to improved electrochemical reduction uniformity of ITO

Copper electroplating is an ideal technique for the metallization of highly efficient silicon heterojunction (SHJ) solar cells due to the unique advantage in the low cost, strong adhesion, and low contact resistance. Achieving these characteristics depends strongly on the seed layer before Cu electroplating. This work reports a potential economical and effective route for electrochemically reducing ITO to assist electroplating of Ni seed layer and increase the adhesion of the metallization grids. Good wettability of electrolyte solution to ITO and the low temperature account for the reduction uniformity. A uniform In,Sn/SnO mixed metal layer is formed on ITO surface after electrochemical reduction. With the assistance of the uniform reduction the adhesion strength of the metallization grid reaches to 9.9 N mm⁻1. Although it is conducted on a small-size ITO-coating Si plate, the present plating is convenient and low-cost for the metallization, which is expected to be suitable for the large-scale commercialization of SHJ solar cells.

Two-Dimensional Semiconductors for State-of-the-Art Complementary Field-Effect Transistors and Integrated Circuits.

As the trajectory of transistor scaling defined by Moore's law encounters challenges, the paradigm of ever-evolving integrated circuit technology shifts to explore unconventional materials and architectures to sustain progress. Two-dimensional (2D) semiconductors, characterized by their atomic-scale thickness and exceptional electronic properties, have emerged as a beacon of promise in this quest for the continued advancement of field-effect transistor (FET) technology. The energy-efficient complementary circuit integration necessitates strategic engineering of both n-channel and p-channel 2D FETs to achieve symmetrical high performance. This intricate process mandates the realization of demanding device characteristics, including low contact resistance, precisely controlled doping schemes, high mobility, and seamless incorporation of high- κ dielectrics. Furthermore, the uniform growth of wafer-scale 2D film is imperative to mitigate defect density, minimize device-to-device variation, and establish pristine interfaces within the integrated circuits. This review examines the latest breakthroughs with a focus on the preparation of 2D channel materials and device engineering in advanced FET structures. It also extensively summarizes critical aspects such as the scalability and compatibility of 2D FET devices with existing manufacturing technologies, elucidating the synergistic relationships crucial for realizing efficient and high-performance 2D FETs. These findings extend to potential integrated circuit applications in diverse functionalities.