Ni Contacts Research Articles

Nickel diffusion into MoS2 and the effect of annealing on contact resistance

Metal-semiconductor interfaces are crucial for the performance of many devices and understanding interactions between material interfaces after processing is therefore of interest. Here, field-effect transistors with Ni contacts are studied to determine the effects of annealing on contact resistance. Contact resistance and total resistance of as-deposited and annealed field-effect transistors with Ni/Ti/Au contacts increase upon annealing, with higher annealing temperatures yielding a greater increase in contact resistance. It appears that Ni diffusion into MoS2 correlates with the observed higher contact resistance, and transmission electron microscopy, energy dispersive spectroscopy, and electron energy loss spectroscopy reveal the presence of Ni in single crystal MoS2 flakes after annealing Ni/MoS2 in ultra-high purity Ar gas at 400 °C. Metal diffusion into 2D semiconductors like MoS2 may help or hurt device performance, and this work highlights the importance of considering the effects metal diffusion may have on contact resistance.

Formation and characterization of Ni, Pt, and Ti stanogermanide contacts on Ge0.92Sn0.08

In this article we provide a comparative and systematic study on contact formation for germanium-tin (GeSn) thin films containing a high percentage of Sn (8 at.%). 20 nm of Nickel (Ni), Titanium (Ti), or Platinum (Pt) was deposited on Ge0.92Sn0.08 layers grown on Ge substrates, and subsequently annealed between 300 and 500 °C to form stanogermanide alloys. Several experimental techniques were employed to characterize the material and the electrical contact behaviour, with the purpose of identifying the most promising stanogermanide contact candidate, in terms of low sheet resistance, low surface roughness and low formation temperature. Among these three different metals we found that, for nanoelectronic applications, nickel-stanogermanide (NiGeSn) was the most promising candidate based on a low sheet resistance combined with a low formation temperature, below 400 °C. PtGeSn showed better behaviour in terms of thermal stability compared with the other two options, while Ti was found to be relatively unreactive under these annealing conditions, resulting in poor TiGeSn formation. For the lowest resistance stanogermanide contact generated, namely NiGeSn formed at 300 °C, detailed lattice resolution Transmission Electron Microscopy imaging, combined with fast Fourier transformation analysis, identified the formation of the Nix-1(GeSn)y-1 phase.

Microstructural Analysis of Ti/Ni Bilayer Ohmic Contacts on 4H-SiC Layers

The micro-structural analysis of Ti/Ni bilayer as Ohmic contacts to n-type 4H-SiC is reported. There was no carbon segregation at the interface between the NiSi layer and the 4H-SiC layer for Ti/Ni contacts, unlike pure Ni contacts. The diffraction pattern image shows the presence of the cubic NiSi film which grows on the SiC surface. The film interface with the SiC was uniform and more planar. An optimized contact in terms of contact morphology was achieved using a bilayer contact Ti/Ni (20/100nm) annealed at 1100 °C for 5 minutes in vacuum.

Improved understanding of metal–graphene contacts

Metal–graphene (M–G) contact resistance (RC) is studied through extensive experimental characterization, Monte–Carlo transport simulations and Density Functional Theory (DFT) analysis. We show that the back–gate voltage dependence of RC cannot be explained only in terms of the resistance of the junction at the edge between contact and channel region. Experiments and DFT calculations indicate a consistent picture where both Ni and Au contacts have a M–G distance larger than the minimum energy distance, and where the M–G distance is crucial in determining the RC value.

Support vector regression (SVR)-based adsorption model for Ni (II) ions removal

Removal of heavy metals with adsorption using low-cost adsorbents has motivated many researchers across the world. In this work, support vector regression (SVR) model is developed for the prediction of the removal efficiency of Ni(II) ions using the waste from tea factory in terms of the independent parameters namely, particle size of adsorbent, pH of the solution, initial Ni (II) ion concentration, flow rate, effluent volume, bed depth and contact time. The SVR-based model is compared with the multiple linear regression (MLR) model using the statistical parameters. The correlation coefficient (R) and the average absolute relative error (AARE) values for the SVR-based has been obtained as 0.993 and 6.88% while those of MLR model they are 0.8393 and 74.54% respectively. The developed state-of-the-art SVR model, based on the structural risk minimization (SRM) principle, is found to predict the experimental values more accurately and is highly generalized.

Effect of bistrifluoromethane sulfonimide treatment on nickel/InAs contacts

In this work, the effects of bis(trifluoromethane) sulfonimide (TFSI) (a superacid) surface treatment on electrical properties of nickel/InAs contacts and InAs material are investigated with transmission line measurements (TLMs). After TFSI treatments on bare InAs TLM patterns, the contact resistance between InAs and Ni contact increased. While for InAs TLM structure passivated with a ZrO2 thin film, the total resistance of InAs decreased drastically after TFSI treatments. X-ray photoelectron spectroscopy measurements revealed that the TFSI reduced the indium oxide at the InAs/ZrO2 interface. This novel passivation method can be adopted in III–V semiconductor device fabrication process to reduce contact resistance and, therefore, enhance device performances, providing a new guidance for III–V fabrication process technology.

Tris(μ2-2-meth-oxy-6-{[(2-sulfido-eth-yl)imino]meth-yl}phenolato)trinickel(II) di-methyl-formamide monosolvate: crystal structure, spectroscopic characterization and anti-bacterial activity.

The title trinuclear nickel(II) complex, [Ni3(C10H11NO2S)3]·C3H7NO, with a Schiff base ligand formed in situ from 2-amino-ethane-thiol and o-vanillin crystallizes in the ortho-rhom-bic space group Pbca. Its asymmetric unit consists of one neutral Ni3 L 3 mol-ecule and one DMF solvent mol-ecule. The solid-state organization of the complex can be described as an insertion of the solvent mol-ecules within the crystallographically independent trinuclear NiII species. Several C-H⋯π edge-to-face inter-actions and π-π stacking inter-actions link the components in the crystal. A first example of a short inter-molecular C-H⋯Ni contact is found. Anti-bacterial in vitro screening revealed that the title compound has anti-bacterial activity, the best effect being against Acinetobacter baumannii.

Adsorption of Ni(II) ions by magnetic activated carbon/chitosan beads prepared from spent coffee grounds, shrimp shells and green tea extract

ABSTRACT Magnetic activated carbon/chitosan composite (MACCS) beads from spent coffee grounds and shrimp shells were synthesized using green tea extract as a crosslinker. The adsorbent was then applied for removal of Ni(II) ions from aqueous solution after carefully characterizing it by various techniques (XRD, FTIR, FE-SEM, EDX, VSM and BET). The adsorption kinetics, isotherms, thermodynamics, the effects of key adsorption factors such as the pH value, initial Ni(II) concentration, contact time, adsorbent dose and temperature were investigated in detail. A possible adsorption mechanism was proposed. The results indicated that the adsorption process was thermodynamically favourable, spontaneous, endothermic, and was best described by the Langmuir isotherm and pseudo-second-order kinetic models. The MACCS beads with an optimum CS to MAC weight ratio estimated as 60:40 gave the maximum monolayer adsorption capacity for Ni(II) ions of 108.70 mg g−1 at 25°C, pH of 6, adsorbent dose of 1.0g L−1 and a contact time of 6 h. The recycling study confirmed that the adsorption ability of MACCS beads towards Ni(II) ions maintained well after five consecutive cycles with the removal efficiency greater than 86.25%. Eventually, the MACCS beads could be used as an environmentally-friendly and highly efficient adsorbent for removal of Ni(II) ions from wastewater due to the advantages of high efficiency, rapid separation and good reusability.

Alternative back contacts for Sb2Se3 solar cells

In this study, alternative back contacts for Sb2Se3 solar cells are explored with an aim to replace commonly used expensive gold electrode. Various low-cost contacts were tested including large work function metals such as Ni and Co. The performance of solar cells with bare metallic electrodes was lower up to 45% when compared to the reference device with Au contact, and was attributed mainly to the large back interface barrier for hole extraction. Additionally, shunt resistance of solar cells decreased significantly when Ni contact were employed as a result of metal diffusion and formation of interface defects. Thermally evaporated thin NiOx was used as a blocking layer for diffusion and mitigating hole extraction barrier. Solar cells with 7 nm of NiOx layer and Ni contact achieved 97% of reference solar cell performance. Over the period of 25 days, solar cells with 7 nm NiOx/Ni as a back contact retained 93% of initial performance, demonstrating that Au contacts can be successfully replaced by low-cost materials and retain high performance.

A Comparative Sorption Study of Ni (II) form Aqueous Solution Using Silica Gel, Amberlite IR-120 and Sawdust

Abstract The presence of heavy metals in water causes serious problems and their treatment before incorporating into the water body is a challenge for researchers. The present study was conducted to compare the sorption study of Ni (II) using silica gel, amberlite IR-120 and sawdust of mulberry wood in batch system under the influence of pH, initial Ni (II) concentration and contact time. It was observed that sorption process was depending upon pH and maximum sorption was achieved at pH 7.0. Kinetic data were well fitted into pseudo-second order kinetic model due to high R2 values and closeness of experimental sorption capacity and calculated sorption capacity of pseudo-second order. Isotherms study showed that Langmuir is one of the most suitable choices to explain sorption data due to high R2 values. The monolayer sorption capacities of silica gel, amberlite IR-120 and sawdust were found to be 33.33, 25.19, and 33.67 mg g−1, respectively. Desorption study revealed that NaCl is one of the most appropriate desorbent. It may be concluded from this study that sawdust is a suitable sorbent due to low cost, abundant availability and recycling of the materials for further study.

Previously unknown quasicrystal periodic approximant found in space

We report the discovery of Al34Ni9Fe2, the first natural known periodic crystalline approximant to decagonite (Al71Ni24Fe5), a natural quasicrystal composed of a periodic stack of planes with quasiperiodic atomic order and ten-fold symmetry. The new mineral has been approved by the International Mineralogical Association (IMA 2018-038) and officially named proxidecagonite, which derives from its identity to periodic approximant of decagonite. Both decagonite and proxidecagonite were found in fragments from the Khatyrka meteorite. Proxidecagonite is the first natural quasicrystal approximant to be found in the Al-Ni-Fe system. Within this system, the decagonal quasicrystal phase has been reported to transform at ~940 °C to Al13(Fe,Ni)4, Al3(Fe,Ni)2 and the liquid phase, and between 800 and 850 °C to Al13(Fe,Ni)4, Al3(Fe,Ni) and Al3(Fe,Ni)2. The fact that proxidecagonite has not been observed in the laboratory before and formed in a meteorite exposed to high pressures and temperatures during impact-induced shocks suggests that it might be a thermodynamically stable compound at high pressure. The most prominent structural motifs are pseudo-pentagonal symmetry subunits, such as pentagonal bipyramids, that share edges and corners with trigonal bipyramids and which maximize shortest Ni–Al over Ni–Ni contacts.

Sub-10-nm-Diameter InGaAs Vertical Nanowire MOSFETs: Ni Versus Mo Contacts

Recently, sub-10-nm-diameter InGaAs vertical nanowire (VNW) MOSFETs have been demonstrated. The key to this achievement was the use of Ni for the top ohmic contact. In this paper, we present a detailed study of the impact of Ni and Mo contacts on the electrical characteristics of highly scaled InGaAs VNW MOSFETs. Sequential annealing experiments are presented that reveal the optimum temperature for each type of contact. A negative temperature dependence of the ON-resistance of 7-nm-diameter Ni-contacted devices suggests the existence of an energy barrier. We also observe an unexpected transconductance and drain-induced barrier loweirng (DIBL) dependence on transistor diameter in Ni-contacted devices as well as abnormal DIBL asymmetry to swapping source and drain. All these results can be explained by Ni diffusing down the nanowire during the contact annealing process, reducing the effective channel length, and creating a Schottky-barrier drain.

Formation of the Uniform Interface Ni/4H-SiC Ohmic Contact with Titanium as Barrier Layer

Nickel (Ni) is the most widely used metal for the formation of ohmic contact on n-type SiC. However, the irregular contact can potentially cause degradation in the device performance. To form the uniform ohmic interface, titanium (Ti) was applied as a barrier layer. Ni/Ti/SiC and Ti/Ni/SiC contact metal structures were prepared, and ohmic contacts were formed using a rapid thermal annealing process. The interfacial properties of both contact metal structures were enhanced by applying the Ti layer. The specific contact resistance of ohmic contacts showed a slightly lower or similar value (~ low 105 Ωcm2) compared with the specific contact resistance values formed from only the Ni contact metal.

Contacting graphene in a 200 mm wafer silicon technology environment

Two different approaches for contacting graphene in a 200 mm wafer silicon technology environment were tested. The key is the opportunity to create a thin SiN passivation layer on top of the graphene protecting it from the damage by plasma processes. The first approach uses pure Ni contacts with a thickness of 200 nm. For the second attempt, Ni is used as the contact metal which substitutes the Ti compared to a standard contact hole filling process. Accordingly, the contact hole filling of this “stacked via” approach is Ni/TiN/W. We demonstrate that the second “stacked Via” is beneficial and shows contact resistances of a wafer scale process with values below 200 Ohm µm.

Dual Control of Molecular Conductance through pH and Potential in Single-Molecule Devices.

One of the principal aims of single-molecule electronics is to create practical devices out of individual molecules. Such devices are expected to play a particularly important role as novel sensors thanks to their response to wide ranging external stimuli. Here we show that the conductance of a molecular junction can depend on two independent stimuli simultaneously. Using a scanning tunnelling microscope break-junction technique (STM-BJ), we found that the conductance of 4,4'-vinylenedipyridine (44VDP) molecular junctions with Ni contacts depends on both the electrochemically applied gate voltage and the pH of the environment. Hence, not only can the Ni|44VDP|Ni junction function as a pH-sensitive switch, but the value of the pH at which switching takes place can be tuned electrically. Furthermore, through the simultaneous control of pH and potential the STM-BJ technique delivers unique insight into the acid-base reaction, including the observation of discrete proton transfers to and from a single molecule.

Silicon carbide of Ni/6H-SiC and Ti/4H-SiC type Schottky diode current-voltage characteristics modelling

On the base of the physical analytical models based on Poisson’s equation, drift–diffusion and continuity equations the forward current–voltage characteristics of 6H-SiC and 4H-SiC type Schottky diode with Ni and Ti Schottky contact have been simulated. It is shown on the base of analysis of current–voltage characteristics in terms of classical thermionic emission theory it is shown that the proposed simulation model of Schottky diode corresponds to the almost “ideal” diode with ideality factor n equals 1.1. Because of this it is determined that the effective Schottky barrier height φB equals 1.57 eV and 1.17 eV for Ni/6H and Ti/4H silicon carbide Schottky diode type, respectively.

(Invited) The Dynamics of Nickelidation for Self-Aligned Contacts to InGaAs Channels

Alloyed and compound contacts, formed by thermal annealing of metal-semiconductor nanowires (NWs), are prescribed for lithography-free self-aligned gate designs. Prior work revealed astounding differences at nanoscale in the formation of such alloys and compounds evoking reevaluation of the thermodynamics, kinetics, and resultant phases during their formation. Some of these studies were carried out by in-situ heating and imaging inside a transmission electron microscopy (TEM) and investigated phase transformations in real-time and at atomic resolutions in elemental semiconductors, i.e. Si and Ge NWs but not in III-V NW channels. Here, we carried out in-situ heating TEM experiments to study the contact metallization process in between Ni contact and In0.53Ga0.47As NW channels fabricated by top-down method, and observed at atomic resolution the detailed ledge formation and movement behaviors in both the NW cross-section and along the NW channel. At typical temperatures at which crystalline Ni2In0.53Ga0.47As phase grow on planar In0.53Ga0.47As surfaces, the NW cross-section experienced a solid-state amorphization step and formed NixIn0.53Ga0.47As (x<2). During this amorphization process, nickelide reacted in a layer-by-layer manner with ledge moving on {111} facets and along <112> directions. The interfacial property between Ni and InGaAs NW was found to significantly influence the reaction kinetics and was captured by a model that was specifically developed for the cross-sectional geometry of NW channels. Finally, the amorphous NixIn0.53Ga0.47As (x<2) phase regrow into a single crystalline Ni2In0.53Ga0.47As phase at temperatures above 375 °C by additional incorporation of Ni adatoms from the contact reservoir. Along the NW channel direction, we found that the reacted interface followed the In0.53Ga0.47As (111) || Ni2In0.53Ga0.47As (0001) atomic plane, and that the ledges nucleated as a train of strained single-bilayers. Once the strain energy in single bilayer ledges was relieved in part by forming misfit dislocations, their velocity decreased permitting the formation of associated single-bilayer ledges, the double-bilayer ledges. Consequently, these nickelide ledges moved with a double-bilayer height that became the unit height of ledges in this phase transformation. Our in-situ studies demonstrated the applicability of interfacial disconnection theory in contact metallization for compound semiconductor nanoscale channels in the ternary to quaternary compound phase transformation, and may guide for the phase selection of crystalline self-aligned contacts in nanoscale channel cross-sections.

Polytherms of porous Ni and Cu contact angles from Sn–Ba and In–Na melts

Polytherms of wetting angles of porous carbonyl nickel and copper (obtained by the redox method) by Sn–Ba and In–Na melts have been experimentally studied. The wetting onset temperatures have been determined. The results of analyzing the sample morphology after crystallization are presented.

Characterization technique for inhomogeneous 4H-SiC Schottky contacts: A practical model for high temperature behavior

In this paper, a characterization technique for 4H-SiC Schottky diodes with varying levels of metal-semiconductor contact inhomogeneity is proposed. A macro-model, suitable for high-temperature evaluation of SiC Schottky contacts, with discrete barrier height non-uniformity, is introduced in order to determine the temperature interval and bias domain where electrical behavior of the devices can be described by the thermionic emission theory (has a quasi-ideal performance). A minimal set of parameters, the effective barrier height and peff, the non-uniformity factor, is associated. Model-extracted parameters are discussed in comparison with literature-reported results based on existing inhomogeneity approaches, in terms of complexity and physical relevance. Special consideration was given to models based on a Gaussian distribution of barrier heights on the contact surface. The proposed methodology is validated by electrical characterization of nickel silicide Schottky contacts on silicon carbide (4H–SiC), where a discrete barrier distribution can be considered. The same method is applied to inhomogeneous Pt/4H–SiC contacts. The forward characteristics measured at different temperatures are accurately reproduced using this inhomogeneous barrier model. A quasi-ideal behavior is identified for intervals spanning 200 °C for all measured Schottky samples, with Ni and Pt contact metals. A predictable exponential current-voltage variation over at least 2 orders of magnitude is also proven, with a stable barrier height and effective area for temperatures up to 400 °C. This application-oriented characterization technique is confirmed by using model parameters to fit a SiC-Schottky high temperature sensor's response.

Characterization of Interface State Density of Ni/p-GaN Structures by Capacitance/Conductance-Voltage-Frequency Measurements**Supported by the Natural Science Foundation of Jiangxi Province under Grant No 20133ACB20005, the Key Program of National Natural Science Foundation of China under Grant No 41330318, the Key Program of Science and Technology Research of Ministry of Education under Grant No NRE1515, the Foundation of Training Academic and Technical

For the frequency range of 1 kHz–10 MHz, the interface state density of Ni contacts on p-GaN is studied using capacitance-voltage (C–V) and conductance-frequency-voltage (G–f–V) measurements at room temperature. To obtain the real capacitance and interface state density of the Ni/p-GaN structures, the effects of the series resistance () on high-frequency (5 MHz) capacitance values measured at a reverse and a forward bias are investigated. The mean interface state densities obtained from the – capacitance and the conductance method are and , respectively. Furthermore, the interface state density derived from the conductance method is higher than that reported from the Ni/n-GaN in the literature, which is ascribed to a poor crystal quality and to a large defect density of the Mg-doped p-GaN.