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A type II heterojunction has been constructed between Cu-GDY and CoGdO 3 , and the participation of photoexcited electrons in the hydrogen evolution process has been significantly enhanced through an ohmic contact, substantially boosting the photocatalytic efficiency. [Display omitted] Although traditional type II heterojunction designs for artificial photosynthesis show promise for photocatalytic hydrogen production, their redox capacity is somewhat limited due to the spatial separation of hydrogen evolution and oxidation reactions at less favorable sites. To overcome this limitation, ohmic junctions based on type II heterojunctions have been designed to enhance hydrogen evolution by transferring electrons to the metal component. In this study, a copper powder graphdiyne (Cu-GDY) composite catalyst with ohmic angle contact was synthesized by coupling copper foil with hexa -hexylbenzene. Incorporating Cu-GDY into CoGdO 3 results in an interleaved band structure forming a type II heterojunction at the contact interface. This configuration overcomes the issue of the unfavorable conduction band position of CoGdO 3 , thereby promoting charge transfer. The internal electric field created by the Fermi level difference between Cu-GDY and CoGdO 3 , increase in REDOX capacity is the main reason for the increase of carrier separation rate. In addition, the plasmonic properties of copper expand the active reaction sites and promote the hydrogen evolution reaction. The composite catalyst exhibits b a hydrogen production rate that is 10.5 times higher than that of the individual catalysts. This work demonstrates that the formation of two distinct contact interfaces between Cu-GDY and CoGdO 3 significantly improves the electron transfer and hydrogen evolution performance. [ABSTRACT FROM AUTHOR]

This work investigates the Ohmic contact mechanism and low resistance Ohmic contact preparation for GaN-based high electron mobility transistors (HEMTs) with GaN/AlN superlattice (SL) barriers. The electrical and microstructural characterization of Ti/Al/Ni/Au contacts shows that the formation of Ohmic contacts primarily depends on the TiN islands formed by Ti diffusion in the barrier layer, which is the main reason for the high contact resistance of GaN/AlN SLs HEMTs under conventional high-temperature annealing. A grid deep-recess technique is proposed to establish direct contact between TiN interfacial layer, the barrier, and the two-dimensional electron gas through the sidewalls. This novel technique achieves an Ohmic contact with a low contact resistance of 0.31 Ω mm at low temperatures (700 °C). Furthermore, increased grid deep-recess density effectively reduces contact resistance due to the additional contribution from the conduction width. It is also noteworthy that after complete removal of the barrier layer, the impact of recess depth on contact characteristics is minimal, greatly reducing the process complexity of grid deep-recess technique. Consequently, GaN/AlN SLs HEMTs fabricated using the grid deep-recess technique exhibit significant improvements in on-resistance, transconductance and saturation current. These results are expected to expand the potential application of GaN/AlN SL barrier layers in radio frequency and power devices. [ABSTRACT FROM AUTHOR]

Adjusting the interfacial transport efficiency of photogenerated electrons and the free energy of hydrogen adsorption through interface engineering is an effective means of improving the photocatalytic activity of semiconductor photocatalysts. Herein, hollow ZnS/NiS nanocages with ohmic contacts containing Zn vacancy (VZn-ZnS/NiS) are synthesized using ZIF-8 as templates. An internal electric field is constructed by Fermi level flattening to form ohmic contacts, which increase donor density and accelerate electron transport at the VZn-ZnS/NiS interface. The experimental and DFT results show that the tight interface and VZn can rearrange electrons, resulting in a higher charge density at the interface, and optimizing the Gibbs free energy of hydrogen adsorption. The optimal hydrogen production activity of VZn-ZnS/NiS is 10,636 mmol h-1 g-1, which is 31.9 times that of VZn-ZnS. This study provides an idea for constructing sulfide heterojunctions with ohmic contacts and defects to achieve efficient photocatalytic hydrogen production. [ABSTRACT FROM AUTHOR]

In this work, metal contacts are fabricated on a p-type Hg1−xCdxTe semiconductor, with composition x = 0.30 and acceptor mercury vacancy concentration in the range of 1016 cm−3, by two different technological processes. Depending on the fabrication process, either non-ohmic contacts, with highly nonlinear current–voltage I(V) characteristics, or ohmic contacts are obtained. Different test patterns are measured at variable temperatures down to 77 K. Isolated small-area contacts, comparable to those in focal plane arrays (FPAs), are used to characterize the metal/semiconductor Schottky barrier energy, while transfer length method (TLM) structures are used to estimate the contact specific resistivity of the ohmic contacts. Classical circular TLM (CTLM) patterns are studied and, in addition, new patterns, referred to as variable-width closed TLM (VW-CTLM), are proposed. The linear I(V) characteristics, measured at variable temperatures down to 77 K, demonstrate that high-performance true ohmic contacts on p-type Hg1−xCdxTe can be obtained. To our knowledge, the contact specific resistivity values for these contacts, in the range 0.7–1.8 × 10−4 ohms cm2 at 77 K, are lower than the published state-of-the-art values. The very stable values of contact resistance over the whole temperature range is coherent with a dominant pure tunnel conduction mechanism through the metal/Hg1−xCdxTe barrier. TLM is used to analyze the ohmic contacts, and in some cases is used to obtain useful information even on some of the non-ohmic contacts, which is somewhat unusual and possibly innovative. [ABSTRACT FROM AUTHOR]

Adjusting the interfacial transport efficiency of photogenerated electrons and the free energy of hydrogen adsorption through interface engineering is an effective means of improving the photocatalytic activity of semiconductor photocatalysts. Herein, hollow ZnS/NiS nanocages with ohmic contacts containing Zn vacancy (VZn-ZnS/NiS) are synthesized using ZIF-8 as templates. An internal electric field is constructed by Fermi level flattening to form ohmic contacts, which increase donor density and accelerate electron transport at the VZn-ZnS/NiS interface. The experimental and DFT results show that the tight interface and VZn can rearrange electrons, resulting in a higher charge density at the interface, and optimizing the Gibbs free energy of hydrogen adsorption. The optimal hydrogen production activity of VZn-ZnS/NiS is 10,636 μmol h−1 g−1, which is 31.9 times that of VZn-ZnS. This study provides an idea for constructing sulfide heterojunctions with ohmic contacts and defects to achieve efficient photocatalytic hydrogen production.

4-probe measurements of surface resistivity, measurements of dark and light current-voltage characteristics, the possibilities of using a thin PdSi film to obtain perfect nano-sized ohmic contacts on the Si(111) surface have been investigated using Auger electron spectroscopy methods in combination with ion etching of the surface. It has been shown that the depth of Ni diffusion in the Ni-Si (111) system is 400 ‑ 500 Å at indoor temperature, and 70 – 80 Å in the Ni-PdSi-Si (111) system. The quality of the ohmic contact in the latter case does not change up to T = 800 K and withstands luminous flux illumination up to F = 1100 lux. It is shown that the resistivity of the PdSi film passes through a minimum at T = 900 – 1000 K. An analysis of the results obtained will be given in the article.

The detection of cations plays a significant role in environmental, pharmaceutical, and clinical analysis. In this study, a uniform Au nanoparticle/PbSe quantum dot heterostructure that promotes the desorption of a variety of cationic analytes (e.g., malachite green, berberine, and choline) was designed based on a layer-by-layer assembly strategy. The fabrication process involved applying a monolayer of AuNPs to a derivatized coverslip, followed by depositing a second layer of PbSe QDs. Through ultraviolet–visible–near-infrared spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and Hall effect measurements, it was revealed that the oxidation of PbSe QDs can induce a transition in electrical transport from n-type to p-type conductivity. This significant change results in an Ohmic contact formed at the heterointerface, which facilitates the transfer of holes from the underlying AuNPs to the surface of PbSe QDs upon UV laser excitation. Thus, the accumulated holes of QDs repel the cationic analytes via Coulombic forces, significantly enhancing the desorption process on the Au/PbSe heterostructure compared to that of the reverse layer configuration. The enhancement in desorption is not attributed to thermal effects, as further confirmed by employing benzylpyridinium as a chemical thermometer. Finally, this hole-driven substrate was applied to quantify choline levels in the human serum from healthy controls and lung cancer patients, and it had high sensitivity and linear correlation for real samples. The results demonstrated that Au/PbSe-assisted LDI-MS offers significant advantages in rapid cation screening and biomedical diagnostics. [ABSTRACT FROM AUTHOR]

The effects of thermal annealing on V‐based electrodes (V/Al/X/Au) with different diffusion barrier metal X are investigated for n‐type Al0.7Ga0.3N. At an annealing temperature of 800 °C, linear current (I)–voltage (V) characteristics are obtained, and the specific contact resistivities of the electrodes for X = Pt, Ni and V are 9.7 × 10−5, 2.3 × 10−4, and 1.8 × 10−4 Ω cm2, respectively. When the annealing temperature is increased to 850 °C, the I–V characteristics become nonlinear. Especially in the case of the V diffusion barrier, significant degradation of the ohmic contact is observed. The coverage of the electrode on the n‐type Al0.7Ga0.3N surface is significantly reduced after thermal annealing at 850 °C, resulting in a decrease in the current value. Furthermore, the formation of V–Al–Au and Al–Au alloys and diffusion of Au to the interface between the n‐type Al0.7Ga0.3N and electrode are found. The Au diffusion preferentially occurs through the domain boundaries of the alloys and causes the deterioration of the ohmic contact properties. In contrast, from the viewpoint of miscibility, Pt and Ni diffusion barriers are more effective than V in suppressing the formation of alloys with Au and then the diffusion of Au. [ABSTRACT FROM AUTHOR]

Various test structures can be used to determine the specific contact resistivity of ohmic contacts. The transmission line model test structure and circular transmission line model test structure are the most commonly used. The analytical expressions of the former are straightforward and effectively describe the electrical behaviour of a contact, while the concentric geometry of the latter eliminates complications during fabrication. In this article, we present a hybrid test structure that combines the advantages of the transmission line and the circular transmission line models. The analytical expressions of the new structure are presented, and its finite‐element modelling is undertaken. The effect of contact geometry on this test structure is also discussed. Using the presented test structure, determining contact parameters does not require any error corrections. [ABSTRACT FROM AUTHOR]

Metallization of diamond with transition metals (TMs) has attracted much attention as they play an important role in the development of precision machining, high‐end thermal management, especially for electronic devices. However, it is found that the solid‐state reaction does not stop at the interface, potentially hampering interface engineering. To unleash the full potential of diamond devices, deeper reactions are investigated in monocrystalline intrinsic diamond metallized with Ti/Pt/Au ohmic contacts combing experiments and theoretical calculations. Apart from exhibiting TiC, graphite, TMs, and diamond nanocrystallites at the interface, a unique ion‐implanted‐like multilayered structure is observed at micrometer depth. TM atoms penetrate through diamond produce a buried amorphous carbon layer under the damaged diamond lattice. In addition, these theoretical calculations reveal that the structural amorphization is catalyzed by the incorporation of TM atoms through vacancy‐mediated diffusion, which induces the closure of the bandgap of the diamond. This facilitates carriers crossing the bandgap via impurity band conduction and promotes the formation of the ohmic contact. This study provides critical insight into the microscopic mechanisms of the metallization between diamonds and TMs and could facilitate the development of diamond‐based electronic devices with a tailored electronic property. [ABSTRACT FROM AUTHOR]

The properties of a metal contact with a p-GaAs layer ~8 nm thick induced by low-energy Ar+ ions on an n-GaAs wafer as a result of the conduction type conversion have been studied. The metal was deposited according to the standard technology on the surface of the semiconductor p-GaAs with a natural oxide layer partially restored when the sample was transferred to a deposition setup. To prevent metallization of the nanolayer the contact was not annealed. Therefore, a Schottky barrier emerged at the interface and a residual oxide layer retained. However, current–voltage characteristics showed that the formed contact is predominantly ohmic. It has been found that a high concentration of ion-induced defects radically reduces the width of the Schottky barrier and ensures the tunneling of holes and electrons of the semiconductor valence band through the barrier in the forward and reverse directions, respectively. It has been shown that ion bombardment of the p-GaAs semiconductor surface makes it possible to obtain an ohmic contact with any metal without annealing. It is concluded that the ion-stimulated modification of the semiconductor and the exclusion of annealing make it possible to obtain a tunnel ohmic contact with an extremely thin p-GaAs nanolayer coated with the residual layer of natural oxide. [ABSTRACT FROM AUTHOR]

The rational construction of interfacial nanostructures of metal/semiconductor (MS) contacted electrocatalysts has a significant impact on improving their intrinsic activities. However, MS contacts are often plagued by a strong Fermi‐level pinning effect, resulting in the formation of the Schottky barrier that affects the adsorption of hydrogen/oxygen intermediates. Herein, an Ohmic contact between metallic Ni3S2 and semiconducting NiMoN is well‐designed, which effectively reduces the electron conduction barriers. The as‐obtained NiMoN/Ni3S2 has remarkable bifunctional water electrolysis performance. At 10 mA·cm−2, the overpotential of hydrogen evolution and oxygen evolution reaction is 70 and 154 mV, respectively. Impressively, the formation of hydroxide during surface reconstruction can avoid the chlorine evolution on the catalyst surface. At an industrial process temperature of 85 °C, it takes only 340 mV for the overall seawater splitting of 500 mA·cm−2. UPS and UV‐VIS diffuse spectra combined with theoretical calculation results confirm that the self‐driven directed electron transfer derived from the Ohmic contact can induce local electron enrichment at the interface region, thus promoting the formation of *O to *OOH. This study provides important insights into the coordinated modulation of built‐in electric fields and the preparation of efficient multifunctional catalysts with a high abundance of active sites. [ABSTRACT FROM AUTHOR]

Since Si‐based Moore's law is physically limited, 2D semiconductors are proposed as successors to continue shrinking the transistor size for more Moore electronics. However, limited by experimental technology bottlenecks, the theoretical predicted superiorities of the 2D transistors over the state‐of‐the‐art Si transistors have been lacking concrete evidence for a decade. In this review, recent exciting experimental breakthroughs for 2D transistors are presented, including gate length miniaturization to a sub‐1 nm limit, electrode contact optimization to the resistance quantum limit, high‐quality dielectric fabrication with an equivalent oxide thickness to sub‐0.5 nm, novel architecture form (2D fin field‐effect transistor), and back‐end‐of‐line integration of directly grown 2D materials on Si complementary metal‐oxide‐semiconductor circuits. Remarkably, an ultrashort channel, Ohmic contact, ballistic transport, and ultrathin dielectric layer are simultaneously satisfied in the 2D InSe transistor, and device performances approaching the theoretical limit are observed. The measured key figures of merit of the ideal 2D InSe transistor are comparable to or even surpass those of the Si transistors. Finally, the challenges and outlook on more Moore electronics based on 2D transistors are highlighted. [ABSTRACT FROM AUTHOR]

As a type of 2D materials, layered double hydroxides (LDHs) have emerged as potential candidates for electrochemical energy storage materials. To address their challenges of limited active sites and sluggish charge transfer kinetics, etc., this work presents an ingenious synchronous topochemical pathway (STP) method that enables the in situ anchoring of numerous nanosized Co9S8 on the rigid layers of LDHs. These n‐type anti‐barrier layers, generated by the ohmic contact between a quasi‐metal (Co9S8) and n‐type semiconductor (LDHs), alter the energy band structure and electron states near the Fermi level, optimizing the intrinsic conductivity and deprotonation reaction barriers of LDH materials. The prepared NiCoAl‐LDHs@Co9S8 (LCS) electrode exhibits remarkable electrochemical capacity (473.2 mAh g−¹ at 1 A g−¹) and operational stability (91.2% capacity retention after 20,000 cycles). Furthermore, an aqueous battery device constructed with LCS cathode and Fe‐Ni sulfide (FNS) anode demonstrates an impressive energy density of 118.5 Wh kg−¹ at a power density of 800 W kg−¹. This generalized structural design strategy achieves multiple enhancements in active sites, charge transfer efficiency, and structural stability of LDH materials, providing insights into the potential relationships between energy band and electrochemical performance in energy storage materials. [ABSTRACT FROM AUTHOR]

The impact of wet treatment using an (NH4)2S-alcohol solution on the interface state of the p-GaN/Ni/Au/Pt contact system and laser diode processing was investigated. Sulfur wet cleaning resulted in reduced surface roughness and contact resistivity. The lowest specific contact resistance (ρc < 1 × 10−4 Ω·cm2) was achieved with samples treated with an (NH4)2S-isopropanol solution, whereas the highest resistivity (ρc = 3.3 × 10−4 Ω·cm2) and surface roughness (Ra = 16 nm) were observed in samples prepared by standard methods. Annealing the contact system in an N2 + O2 + H2O atmosphere caused degradation through species inter-diffusion and metal-metal solid solution formation, irrespective of the preparation method. Standard prepared substrates developed a thin GaN-Au intermediate layer at the interface after heat treatment. Enhanced adhesion and the absence of GaN decomposition were observed in samples additionally cleaned with the (NH4)2S-solvent solution. Complete oxidation of nickel to NiO was observed in samples that underwent additional sulfur solution treatment. The intensity of metal species mixing and nickel oxidation was influenced by the metal diffusion rate and was affected by the initial state of the GaN substrate obtained through different wet treatment methods. [ABSTRACT FROM AUTHOR]

A MEMS piezoresistive sensor for measuring accelerations greater than 100,000 g (about 106 m/s2) is described in this work. To enhance the performance of the sensor, specifically widening its measurement range and natural frequency, a cross-beam construction with a center block was devised, and a Wheatstone bridge was formed by placing four piezoresistors at the ends of the fixed beams to convert acceleration into electricity. The location of the varistor was determined using the finite element approach, which yielded the optimal sensitivity. Additionally, a reliable Pt-Ti-Pt-Au electrode was designed to solve the issue of the electrode failing under high impact and enhancing the stability of the ohmic contact. The accelerometer was fabricated using MEMS technology, and the experiment with a Hopkinson pressure bar and hammering was conducted, and the bias stability was measured. It had a sensitivity of 1.06 μV/g with good linearity. The simulated natural frequency was 633 kHz The test result revealed that the accelerometer can successfully measure an acceleration of 100,000 g. [ABSTRACT FROM AUTHOR]

The degradation of an n++ GaN regrown ohmic contact in a MIS-HEMT device induced by ion beam etching (IBE) damages and relevant mechanisms have been studied. Abnormal I–V behaviors of the etched n++ GaN were observed by the transfer length method using a Ti/Al/Ni/Au stack as the contact metal, and it can be recovered with the assistance of post-metallization rapid thermal annealing. According to further analysis, we speculate that the degradation of the ohmic contact originates from the preferential loss of nitrogen by IBE, which boosts the oxygen incorporation and formation of an oxide layer isolating the contact metal from the n++ GaN. [ABSTRACT FROM AUTHOR]

Energy dispersive X-ray microanalysis is one of the main methods for determining the elemental composition of matter. Possessing high locality and a relatively shallow penetration depth of the electron beam (

Effective Ohmic contact between metals and their conductive channels is a crucial step in developing high-performance Ga2O3-based transistors. Distinct from bulk materials, excess thermal energy of the annealing process can destroy the low-dimensional material itself. Given the thermal budget concern, a feasible and moderate solution (i.e., Ar-containing plasma treatment) is proposed to achieve effective Ohmic junctions with (100) β-Ga2O3 nanosheets. The impact of four kinds of plasma treatments (i.e., gas mixtures SF6/Ar, SF6/O2/Ar, SF6/O2, and Ar) on (100) β-Ga2O3 crystals is comparatively studied by X-ray photoemission spectroscopy for the first time. With the optimal plasma pre-treatment (i.e., Ar plasma, 100 W, 60 s), the resulting β-Ga2O3 nanosheet field-effect transistors (FETs) show effective Ohmic contact (i.e., contact resistance RC of 104 Ω·mm) without any post-annealing, which leads to competitive device performance such as a high current on/off ratio (>107), a low subthreshold swing (SS, 249 mV/dec), and acceptable field-effect mobility ( μ e f f , ~21.73 cm2 V−1 s−1). By using heavily doped β-Ga2O3 crystals (Ne, ~1020 cm−3) for Ar plasma treatments, the contact resistance RC can be further decreased to 5.2 Ω·mm. This work opens up new opportunities to enhance the Ohmic contact performance of low-dimensional Ga2O3-based transistors and can further benefit other oxide-based nanodevices. [ABSTRACT FROM AUTHOR]

Recently, rhenium (Re) based ohmic contacts to GaN have been studied for their low resistivity, smooth surface morphology, and sharp edge acuity at low annealing temperatures. In this work, we discuss the evolution of surface microstructures for Re‐Al‐Ni‐Au ohmic contacts on n‐GaN as a function of Re layer thickness and annealing temperature. For all Re thicknesses, the Al and Ni segregate into agglomerates that increase in size with increasing annealing temperature. These agglomerates are surrounded by Al‐Au films. Along with the underlying Re layer, they form different crystallographic phases of Re‐Al‐Ni, Al6Re, AlAu2, and Al2Au5. This, along with the formation of Re‐N phases at the metal‐semiconductor interface leads to low resistivity ohmic contacts on n‐GaN. Investigating the evolution of the contact microstructure is an important step in understanding the behavior of the Re‐based ohmic contact system. [ABSTRACT FROM AUTHOR]

Photo-excited holes usually migrate to the surface of the catalyst and rapidly recombine with electrons, reducing the photocatalytic reduction efficiency of uranium(VI) (U(VI)) in radioactive wastewater. Consequently, we employed a straightforward synthesis technique to meticulously shape and manipulate the morphology of CdS to precisely construct CdS-Ni dandelion-like composites with different aspect ratios. Briefly, the introduction of crystal facet homojunction with Ohmic contacts in this unique morphology siqnificantly improves the photocatalytic efficiency. Temperature-dependent photoluminescence spectroscopy (TD-PL) verifies that the composite material positively effects on the dissociation of excitons. Within 30 min, CdS(002)/(102)/Ni-4 removed 98% of the uranium content in solution and showed a rather high apparent rate constant (0.114 min−1), which was 4.8 times higher than that of CdS nanospheres (NSs) (0.024 min−1) and 3.7 times higher than that of CdS nanorods (NRs) (0.031 min−1). This is much higher the most reported photocatalysts for U(VI) reduction. Even after 5 consecutive cycles, the photocatalytic efficiency only decreased by 7%. This offers a fresh perspective on constructing a new perspective for building a green, efficient, and multi mechanism collaborative catalytic system to remediate environmental pollution. [ABSTRACT FROM AUTHOR]

In this paper, the contact resistance of AlGaN/GaN high electron mobility transistor (HEMT) was improved by introducing nanoscale hole arrays in ohmic regions, and the DC characteristics of the conventional structure and nanohole etching structure for HEMTs were measured for comparison. Sub-10 nm nanoholes were patterned on the ohmic area surface of AlGaN using electron beam lithography and a low-temperature short-time development. Various dwell times of e-beam exposure from 5 to 30 μs were investigated and the corresponding contact resistance of the nano hole etching structure and planar structure were compared by the transmission line model (TLM) method. We observed a reduced contact resistance from 1.82 to 0.47 Ω-mm by performing a dwell time of 5 μs of exposure for nanohole formation compared to the conventional structure. Furthermore, the DC characteristics demonstrate that the maximum drain current for HEMTs was enhanced from 319 to 496 mA/mm by utilizing this optimized ohmic contact. These results show that devices with sub-10 nm nanohole ohmic contacts exhibit an improved contact resistance over the conventional structure, optimizing device performance for HEMTs, including a lower on-resistance and higher maximum drain current. [ABSTRACT FROM AUTHOR]

4-probe measurements of surface resistivity, measurements of dark and light current-voltage characteristics, the possibilities of using a thin PdSi film to obtain perfect nano-sized ohmic contacts on the Si(111) surface have been investigated using Auger electron spectroscopy methods in combination with ion etching of the surface. It has been shown that the depth of Ni diffusion in the Ni-Si (111) system is 400 - 500 Å at indoor temperature, and 70 – 80 Å in the Ni-PdSi-Si (111) system. The quality of the ohmic contact in the latter case does not change up to T = 800 K and withstands luminous flux illumination up to F = 1100 lux. It is shown that the resistivity of the PdSi film passes through a minimum at T = 900 – 1000 K. An analysis of the results obtained will be given in the article. [ABSTRACT FROM AUTHOR]

We investigated the optimization effects of KOH solution treatment and SiN x sacrificial layer treatment on the contact characteristics of V/Al/Ni/Au on plasma-etched n-AlGaN. The results showed that the contacts on n-Al0.5Ga0.5N with both surface treatments are truly Ohmic in nature, while the contacts on untreated plasma-etched samples are still rectifying. Surface atomic concentration analysis revealed that both surface treatment methods effectively reduced the nitrogen vacancies on n-AlGaN induced by plasma etching, which mostly act as acceptor-like states, leading to severe compensation and hindering of the formation of Ohmic contact. Moreover, the operating voltage was reduced by 0.9 V at 20 mA for 285 nm ultraviolet light-emitting diodes, demonstrating that the surface treatment could work well for plasma-etched n-AlGaN Ohmic contacts. [ABSTRACT FROM AUTHOR]

In this work, the electrical characteristics of the ohmic contacts fabricated by laser-induced diffusion of cobalt dopants in silicon substrates were studied. The main parameters affecting these characteristics are the laser fluence and number of laser pulses used for irradiation. An Nd:YAG laser operating in Q-switching mode and wavelength of 1064nm was used to irradiate the contact region of cobalt on silicon substrate to induce the diffusion of cobalt dopants into the structure of the silicon. The electrical measurements showed a reasonable modification as the ochmic contact resistance decreased with increasing laser fluence as a result of the enhanced diffusion of metallic dopants into the semiconductor substrate. [ABSTRACT FROM AUTHOR]

Abstract Two‐dimensional (2D) materials with free of dangling bonds have the potential to serve as ideal channel materials for the next generation of field‐effect transistors (FETs) due to their atomic‐thin and excellent electronic properties. However, the performance of 2D materials‐based FETs is still dictated by the interface between electrodes/dielectrics and 2D materials. Several technical challenges such as improving device stability, reducing contact resistance, and advancing mobility need to be overcome. Herein, we focus on the effects of atomic‐scale interface engineering on the contact resistance and dielectric layer for 2D FETs. Universal strategies we consider to achieve ohmic contact and develop high‐quality, defect‐free dielectric layers are provided. Furthermore, advancing the performance of 2D materials‐based FETs and binding to silicon substrates are briefly analyzed.

High-Al-content n-AlGaN ohmic contact is very important for deep ultraviolet optoelectrical devices. However, it often suffers from the etching damages formed in inductively coupled plasma (ICP) etching. In this paper, the effects of ICP etching parameters on n-Al0.5Ga0.5N ohmic contact, including RF power, ICP power, and etching gas, were systematically investigated and analyzed by X-ray photoelectron spectroscopy and circular transmission line model. Finally, n-Al0.5Ga0.5N ohmic contact was achieved with a low specific contact resistivity of 8.7×10-4 Ω·cm2, and AlGaN-based UVC light-emitting diodes (LEDs) showed a low operation voltage of only 5.6 V at the injection current density of 16 A/cm2.

Contact scaling is a major challenge in nano complementary metal–oxide–semiconductor (CMOS) technology, as the surface roughness, contact size, film thicknesses, and undoped substrate become more problematic as the technology shrinks to the nanometer range. These factors increase the contact resistance and the nonlinearity of the current–voltage characteristics, which could limit the benefits of the further downsizing of CMOS devices. This review discusses issues related to the contact size reduction of nano CMOS technology and the validity of the Schottky junction model at the nanoscale. The difficulties, such as the limited doping level and choices of metal for band alignment, Fermi-level pinning, and van der Waals gap, in achieving transparent ohmic contacts with emerging two-dimensional materials are also examined. Finally, various methods for improving ohmic contacts' characteristics, such as two-dimensional/metal van der Waals contacts and hybrid contacts, junction doping technology, phase and bandgap modification effects, buffer layers, are highlighted. [ABSTRACT FROM AUTHOR]

The newly prepared monolayer (ML) SiAs is expected to be a candidate channel material for next-generation nano-electronic devices in virtue of its proper bandgap, high carrier mobility, and anisotropic properties. The interfacial properties in ML SiAs field-effect transistors are comprehensively studied with electrodes (graphene, V2CO2, Au, Ag, and Cu) by using ab initio electronic structure calculations and quantum transport simulation. It is found that ML SiAs forms a weak van der Waals interaction with graphene and V2CO2, while it forms a strong interaction with bulk metals (Au, Ag, and Cu). Although ML SiAs has strong anisotropy, it is not reflected in the contact property. Based on the quantum transport simulation, ML SiAs forms n-type lateral Schottky contact with Au, Ag, and Cu electrodes with the Schottky barrier height (SBH) of 0.28 (0.27), 0.40 (0.47), and 0.45 (0.33) eV along the a (b) direction, respectively, while it forms p-type lateral Schottky contact with a graphene electrode with a SBH of 0.34 (0.28) eV. Fortunately, ML SiAs forms an ideal Ohmic contact with the V2CO2 electrode. This study not only gives a deep understanding of the interfacial properties of ML SiAs with electrodes but also provides a guide for the design of ML SiAs devices. [ABSTRACT FROM AUTHOR]

Tunnel junctions (TJs) offer a unique approach to utilizing nonequilibrium tunneling injection of holes and have demonstrated potential applications in ultraviolet (UV) emitters. However, high operating voltage caused by the wide bandgap of the III‐nitrides has impeded the further promotion of TJ. Here, 275 nm n+‐Al0.45Ga0.55N/p+‐Al0.5Ga0.5N ultrathin tunnel junction (UTJ) deep‐UV light‐emitting diodes (LEDs) are developed for minimizing the electrical losses and achieve, to the current knowledge, the lowest operating voltage (5.7 V) at 300 mA reported to date. This study discovers that Mg‐Si co‐doping occurs in the n+‐Al0.45Ga0.55N layer during the growth of n+‐Al0.45Ga0.55N/p+‐Al0.5Ga0.5N UTJ due to the memory and diffusion effect of Mg, which leads to the formation of Ohmic contact between high‐work‐function Ni/Au and Mg‐Si co‐doped n+‐ Al0.45Ga0.55N layer in UTJ. The Zener diode, fluorine resin, and optimally designed glass lens are incorporated into the chip encapsulation to enhance the reliability and optical performance of the device. Furthermore, a high‐efficiency sterilization deep‐UV light source is developed integrated with 120 UTJ deep‐UV LED chips. Complete surface inactivation at a long irradiation distance (20 cm) is achieved within only seconds using the high‐power sterilization deep‐UV light source. These results indicate that UTJ is promising in developing deep UV LEDs and their integrated light sources. [ABSTRACT FROM AUTHOR]

The electrical properties of ohmic contacts are classically investigated by using the transfer length method (TLM). In the literature, the TLM patterns are fabricated onto different substrate configurations, especially directly onto the 4H-SiC wafers. But, due to the high doping level of commercial substrates, the current is not confined close to the contact and, in this case, the specific contact resistance (SCR) value is overestimated. In this article, we propose, by the means of simulations, to investigate the influence of the layer under the contact towards the estimation of the SCR. The simulation results highlight that, for an accurate determination of the SCR values, an isolation layer between the contact and the silicon carbide substrate is mandatory. Thus, we have determined the characteristics (doping level and thickness) of a suitable isolation layer compatible with SCR values ranging from 10−3 to 10−6 Ω·cm2. [ABSTRACT FROM AUTHOR]