Nickel Germanide Research Articles

Ti Interlayer Mediated Uniform NiGe Formation under Low-Temperature Microwave Annealing

The reactions between nickel and germanium are investigated by the incorporation of a titanium interlayer on germanium (100) substrate. Under microwave annealing (MWA), the nickel germanide layers are formed from 150 °C to 350 °C for 360 s in ambient nitrogen atmosphere. It is found that the best quality nickel germanide is achieved by microwave annealing at 350 °C. The titanium interlayer becomes a titanium cap layer after annealing. Increasing the diffusion of Ni by MWA and decreasing the diffusion of Ni by Ti are ascribed to induce the uniform formation of nickel germanide layer at low MWA temperature.

Facile Access to an Active γ-NiOOH Electrocatalyst for Durable Water Oxidation Derived From an Intermetallic Nickel Germanide Precursor.

Identifying novel classes of precatalysts for the oxygen evolution reaction (OER by water oxidation) with enhanced catalytic activity and stability is a key strategy to enable chemical energy conversion. The vast chemical space of intermetallic phases offers plenty of opportunities to discover OER electrocatalysts with improved performance. Herein we report intermetallic nickel germanide (NiGe) acting as a superior activity and durable Ni‐based electro(pre)catalyst for OER. It is produced from a molecular bis(germylene)‐Ni precursor. The ultra‐small NiGe nanocrystals deposited on both nickel foam and fluorinated tin oxide (FTO) electrodes showed lower overpotentials and a durability of over three weeks (505 h) in comparison to the state‐of‐the‐art Ni‐, Co‐, Fe‐, and benchmark NiFe‐based electrocatalysts under identical alkaline OER conditions. In contrast to other Ni‐based intermetallic precatalysts under alkaline OER conditions, an unexpected electroconversion of NiGe into γ‐NiIIIOOH with intercalated OH−/CO3 2− transpired that served as a highly active structure as shown by various ex situ methods and quasi in situ Raman spectroscopy.

Facile Access to an Active γ‐NiOOH Electrocatalyst for Durable Water Oxidation Derived From an Intermetallic Nickel Germanide Precursor

AbstractIdentifying novel classes of precatalysts for the oxygen evolution reaction (OER by water oxidation) with enhanced catalytic activity and stability is a key strategy to enable chemical energy conversion. The vast chemical space of intermetallic phases offers plenty of opportunities to discover OER electrocatalysts with improved performance. Herein we report intermetallic nickel germanide (NiGe) acting as a superior activity and durable Ni‐based electro(pre)catalyst for OER. It is produced from a molecular bis(germylene)‐Ni precursor. The ultra‐small NiGe nanocrystals deposited on both nickel foam and fluorinated tin oxide (FTO) electrodes showed lower overpotentials and a durability of over three weeks (505 h) in comparison to the state‐of‐the‐art Ni‐, Co‐, Fe‐, and benchmark NiFe‐based electrocatalysts under identical alkaline OER conditions. In contrast to other Ni‐based intermetallic precatalysts under alkaline OER conditions, an unexpected electroconversion of NiGe into γ‐NiIIIOOH with intercalated OH−/CO32− transpired that served as a highly active structure as shown by various ex situ methods and quasi in situ Raman spectroscopy.

Formation of Thin NiGe Films by Magnetron Sputtering and Flash Lamp Annealing.

The nickel monogermanide (NiGe) phase is known for its electrical properties such as low ohmic and low contact resistance in group-IV-based electronics. In this work, thin films of nickel germanides (Ni–Ge) were formed by magnetron sputtering followed by flash lamp annealing (FLA). The formation of NiGe was investigated on three types of substrates: on amorphous (a-Ge) as well as polycrystalline Ge (poly-Ge) and on monocrystalline (100)-Ge (c-Ge) wafers. Substrate and NiGe structure characterization was performed by Raman, TEM, and XRD analyses. Hall Effect and four-point-probe measurements were used to characterize the films electrically. NiGe layers were successfully formed on different Ge substrates using 3-ms FLA. Electrical as well as XRD and TEM measurements are revealing the formation of Ni-rich hexagonal and cubic phases at lower temperatures accompanied by the formation of the low-resistivity orthorhombic NiGe phase. At higher annealing temperatures, Ni-rich phases are transforming into NiGe, as long as the supply of Ge is ensured. NiGe layer formation on a-Ge is accompanied by metal-induced crystallization and its elevated electrical resistivity compared with that of poly-Ge and c-Ge substrates. Specific resistivities for 30 nm Ni on Ge were determined to be 13.5 μΩ·cm for poly-Ge, 14.6 μΩ·cm for c-Ge, and 20.1 μΩ·cm for a-Ge.

Nickel Texture Adjustment on Si and Ge and Its Impact on Nickel Silicide and Germanide

Nickel silicide offers advantages over cobalt silicide, but comes along with possible elevated p source-drain leakage currents. In this paper, the effect of deposition temperature on the Ni texture on Si and Ge and its correlation to the silicide and germanide texture is studied for a better control of their properties. A shift from fiber texture to epitaxial Ni growth and an impact on the silicide and germanide texture was found.

Nickel Germanide Thin Films by Atomic Layer Deposition

This work presents preparation of nickel germanide (Ni2Ge) thin films by atomic layer deposition (ALD). The films were grown using NiCl2(tmpda) (tmpda = N,N,N′,N′,-tetramethyl-1,3-propanediamine) a...

Improvement of thermal stability of nickel germanide using nitrogen plasma pretreatment for germanium-based technology

Improvement of thermal stability of nickel germanide using nitrogen plasma pretreatment for germanium-based technology

Low contact resistance of NiGe/p-Ge by indium segregation during Ni germanidation

Herein, indium-doped p-type source/drain was introduced and the redistribution of indium (In) during the formation of a nickel germanide at the NiGe/Ge interface was characterized. Our results show that In segregates at the NiGe/p-Ge interface during Ni germanidation. The specific contact resistivity, ρc between the NiGe and p-Ge layer, with a substantial low value of 4.04 × 10−8 Ωcm2 was obtained with the activation by rapid thermal annealing (RTA) at 650°C for 10 s. From this result, it can be concluded that Ge p-type metal–oxide–semiconductor field-effect transistors (Ge pMOSFETs) with low parasitic resistance source/drains could be realized by this In segregation.

Niobium-bearing arsenides and germanides from elemental mixtures not involving niobium: a new twist to an old problem in solid-state synthesis.

Three isostructural transition-metal arsenides and germanides, namely niobium nickel arsenide, Nb0.92(1)NiAs, niobium cobalt arsenide, NbCoAs, and niobium nickel germanide, NbNiGe, were obtained as inadvertent side products of high-temperature reactions in sealed niobium containers. In addition to reporting for the very first time the structures of the title compounds, refined from single-crystal X-ray diffraction data, this article also serves as a reminder that niobium containers may not be suitable for the synthesis of ternary arsenides and germanides by traditional high-temperature reactions. Synthetic work involving alkali or alkaline-earth metals, transition or early post-transition metals, and elements from groups 14 or 15 under such conditions may yield Nb-containing products, which at times could be the major products of such reactions.

Improving the morphological stability of nickel germanide by tantalum and tungsten additions

To enhance the morphological stability of NiGe, a material of interest as a source drain-contact in Ge-based field effect transistors, Ta or W, is added as either an interlayer or a capping layer. The efficacy of this Ta or W addition is evaluated with pure NiGe as a reference. While interlayers increase the NiGe formation temperature, capping layers do not retard the NiGe formation. Regardless of the initial position of Ta or W, the morphological stability of NiGe against agglomeration can be improved by up to 100 °C. The improved thermal stability can be ascribed to an inhibited surface diffusion, owing to Ta or W being located on top of NiGe after annealing, as confirmed by means of transmission electron microscopy, Rutherford backscattering spectrometry, and atom probe tomography. The latter also shows a 0.3 at. % solubility of Ta in NiGe at 450 °C, while no such incorporation of W is detectable.

Synthesis of nickel germanide (Ge12Ni19) nanoparticles for durable hydrogen evolution reaction in acid solutions.

Desigining advanced materials as electrochemical catalysts for the hydrogen evolution reaction (HER) has caught great attention owing to the growing demand for clean and renewable energy. Nickel (Ni)-based compounds and alloys are promising non-noble-metal electrocatalysts due to their low cost and high activity. However, in most cases, Ni-based compounds and alloys have low durability in acid electrolyte, which limits their application in the electrolytic processes. In this study, monoclinic Ge12Ni19 nanoparticles were synthesized and exhibited high electrocatalytic activity and stability for the HER in acidic solution. Ge12Ni19 nanoparticles achieve an overpotential of 190 mV at cathodic current density of 10 mA cm-2 and a Tafel slope of 88.5 mV per decade in 0.50 M H2SO4 electrolyte. Moreover, the performance is maintained after a 10 000-cycle CV sweep (-0.3 to +0.1 V vs. RHE) or under a static overpotential of -0.7 V vs. RHE for 24 hours. The reported electrocatalytic performance of the Ge12Ni19 nanoparticles sufficiently proves the excellent endurance at lower required active overpotentials in acidic solution, enabling the broad applications of the Ni-based electrocatalysts. Finally, a large-area (5 cm2) electrocatalyst for HER was demonstrated for the first time. The great efficiency of the energy conversion performance sufficiently represented the potential of Ge12Ni19 nanoparticles as electrocatalysts in commercial fuel cells.

Formation of Low-Resistivity Nickel Germanide Using Atomic Layer Deposited Nickel Thin Film

Nickel germanide (NiGe) was formed from atomic layer deposition (ALD) Ni on Ge and a subequent annealing process; the Ni film with low resistivity ( $34~\mu \Omega \cdot \text {cm}$ ) at 15 nm was obtained by N2 + H2 plasma treatment after Ni precursor injection. The formed NiGe film showed low specific contact resistivity ( $\rho _{c})$ values of 9.01 $\mu \Omega \cdot \text {cm}^{2}$ for an NiGe/n+Ge contact and 3.61 $\mu \Omega \cdot \text {cm}^{2}$ for an NiGe/p+Ge contact. These values were comparable to those obtained using sputtered Ni. In addition, the ALD process-based NiGe showed excellent thermal/electrical stability up to 600 °C.

Experimental Realization of Thermal Stability Enhancement of Nickel Germanide Alloy by Using TiN Metal Capping

In this paper, we demonstrated the enhancement of thermal stability of nickel germanide (NiGe) alloy up to 600 °C by using titanium nitride (TiN) metal capping. A high ${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ ratio of $2.9 \times 10^{5}$ was achieved by capping TiN metal on Ni for NiGe alloy formation at 600 °C. Detailed analyses were performed for realizing the mechanism for TiN capping on NiGe/Ge, including vertical element diffusion profile observation through depth-profiling X-ray photoelectron spectroscopy (XPS), element diffusion distribution by energy-dispersive X-ray spectroscopy mapping, and direct junction leakage current path detection by conductive atomic force microscopy. The experimental results indicated that TiN capping can reduce the risk of agglomeration and form a graded NiGe/Ge Schottky junction that is beneficial for suppressing the degradation of junction leakage. Subsequently, we compared the electrical performance of TiN/NiGe/n-Ge at various N/Ti ratios of TiNs. Based on the depth-profiling XPS results and electrical performance, TiN with an N/Ti ratio of approximately 1:1 can resist the Ni and Ge diffusion, which facilitates the suppression of the agglomeration process. However, the TiN capping layers with an N/Ti ratio of less than approximately 1:1 (Ti-rich) were not favorable for resisting Ni and Ge diffusion.

Formation of nickel germanides from Ni layers with thickness below 10 nm

The authors have studied the reaction between a Ge (100) substrate and thin layers of Ni ranging from 2 to 10 nm in thickness. The formation of metal-rich Ni5Ge3 was found to precede that of the monogermanide NiGe by means of real-time in situ x-ray diffraction during ramp-annealing and ex situ x-ray pole figure analyses for phase identification. The observed sequential growth of Ni5Ge3 and NiGe with such thin Ni layers is different from the previously reported simultaneous growth with thicker Ni layers. The phase transformation from Ni5Ge3 to NiGe was found to be nucleation-controlled for Ni thicknesses <5 nm, which is well supported by thermodynamic considerations. Specifically, the temperature for the NiGe formation increased with decreasing Ni (rather Ni5Ge3) thickness below 5 nm. In combination with sheet resistance measurement and microscopic surface inspection of samples annealed with a standard rapid thermal processing, the temperature range for achieving morphologically stable NiGe layers was identified for this standard annealing process. As expected, it was found to be strongly dependent on the initial Ni thickness.

The selective synthesis of nickel germanide nanowires and nickel germanide seeded germanium nanowires within a solvent vapour growth system

We report the formation of NiGe nanowires by the thermal decomposition of diphenylgermane, in the presence of a bulk Ni foil, in a solvent vapor growth system. The reaction occurs by the initial formation of a NiGe layer on the foil which progresses to the growth of nanowire occlusions of the same phase, typically 40 nm in diameter. Switching the substrate from bulk Ni foil to an evaporated layer of Ni results in the growth of NiGe seeded germanium nanowires, in high yield. The nanowires were characterized using high resolution scanning electron microscopy, X-ray diffraction, and high resolution transmission electron microscopy.

Phase formation and texture of thin nickel germanides on Ge(001) and Ge(111)

We studied the solid-phase reaction between a thin Ni film and a single crystal Ge(001) or Ge(111) substrate during a ramp anneal. The phase formation sequence was determined using in situ X-ray diffraction and in situ Rutherford backscattering spectrometry (RBS), while the nature and the texture of the phases were studied using X-ray pole figures and transmission electron microscopy. The phase sequence is characterized by the formation of a single transient phase before NiGe forms as the final and stable phase. X-ray pole figures were used to unambiguously identify the transient phase as the ϵ-phase, a non-stoichiometric Ni-rich germanide with a hexagonal crystal structure that can exist for Ge concentrations between 34% and 48% and which forms with a different epitaxial texture on both substrate orientations. The complementary information gained from both RBS and X-ray pole figure measurements revealed a simultaneous growth of both the ϵ-phase and NiGe over a small temperature window on both substrate orientations.

The <inline-formula> <tex-math notation="LaTeX">${\sim } 3\,{\times } 10^{20}$ </tex-math></inline-formula> cm<inline-formula> <tex-math notation="LaTeX">$^{-3}$ </tex-math></inline-formula> Electron Concentration and Low Specific Contact Resistivity of Phosphorus-Doped Ge on Si by <italic>In-Situ</italic> Chemical Vapor Deposition Doping and Laser Annealing

The phosphorus incorporation by chemical vapor deposition and activation by laser annealing reaches the electron concentration of $\sim 3\times 10^{20}$ cm $^{-3}$ . The pulsed laser not only activates the phosphorus but also produces the biaxial tensile strain of 0.35%. With the nickel germanide contact, the specific contact resistivity reaches as low as $1.5\times 10^{-8}~\Omega $ -cm2 by greatly reducing the tunneling distance. Due to 4% misfit between Ge and Si, there are still misfit dislocations near the Ge/Si interface. The misfit dislocations at the Ge/Si interface lead to the ideality factor of 1.6 for the Ge/Si hetero-junction diode with ON/OFF ratio of $\sim 1\times 10^{5}$ .

Growth and evolution of nickel germanide nanostructures on Ge(001)

Nickel germanide is deemed an excellent material system for low resistance contact formation for future Ge device modules integrated into mainstream, Si-based integrated circuit technologies. In this study, we present a multi-technique experimental study on the formation processes of nickel germanides on Ge(001). We demonstrate that room temperature deposition of ∼1 nm of Ni on Ge(001) is realized in the Volmer–Weber growth mode. Subsequent thermal annealing results first in the formation of a continuous NixGey wetting layer featuring well-defined terrace morphology. Upon increasing the annealing temperature to 300 °C, we observed the onset of a de-wetting process, characterized by the appearance of voids on the NixGey terraces. Annealing above 300 °C enhances this de-wetting process and the surface evolves gradually towards the formation of well-ordered, rectangular NixGey 3D nanostructures. Annealing up to 500 °C induces an Ostwald ripening phenomenon, with smaller nanoislands disappearing and larger ones increasing their size. Subsequent annealing to higher temperatures drives the Ni-germanide diffusion into the bulk and the consequent formation of highly ordered, {111} faceted Ni-Ge nanocrystals featuring an epitaxial relationship with the substrate Ni-Ge (101); (010) || Ge(001); (110).

Structure determination of the ordered [formula omitted] phase of Ni2Si and Ni2Ge surface alloys on Ni(111) via low-energy electron diffraction

The 3×3R30° structures of 2-D nickel silicide and nickel germanide surface alloys on Ni(111) were investigated using quantitative low-energy electron diffraction analysis. The unit cells of the determined silicide and germanide structures contain two Ni atoms and one Si or Ge atom, corresponding to the chemical compositions Ni2Si and Ni2Ge, respectively. Both the Si and Ge atoms adopt substitutional face-centered cubic hollow sites to sit on the Ni(111) substrates, and the alloy surfaces exhibit a slight corrugation. The NiSi and NiGe distances were 2.44 and 2.56Å, respectively, and corresponded well to their respective empirical radii. It was also found that the Ni atoms in the second and third layers moved toward the Si or Ge atom sites from their bulk crystal positions. These results indicate rather strong interactions of the Ni atoms with both the Si and Ge atoms at the surface, leading to trapping of the Si and Ge atoms at the substitutional sites without diffusion into the bulk.

ChemInform Abstract: Solid‐state Reaction of Nickel Silicide and Germanide Contacts to Semiconductor Nanochannels

The surge in advancing the materials science of solid-state reactions for nanoscale contacts to advanced semiconductor devices necessitates a comprehensive dissemination and discussion on recent progress. The objective of this work is to review the notable developments in compound and alloy contact formation to nanoscale nanowire channels made of germanium, silicon, and their heterostructures, and to develop a unifying framework for understanding the significantly distinct reaction behaviors from those commonly observed in bulk. The Ni-based compound and alloy contacts are used as a platform to highlight the size-relevant, thermodynamic, and kinetic differences, and their key material, reaction, and electronic parameters and properties are summarized. Special attention is given to the interplay between the compound/alloy contact structure and the resultant electronic properties.