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

Abstract

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).

Nanometer-Scale Ge-Based Adaptable Transistors Providing Programmable Negative Differential Resistance Enabling Multivalued Logic

“…For contact formation, a thermally induced exchange reaction between the Ge NWs and Al contact pads was used to embed Ge channels contacted by quasi-1D monocrystalline Al NW leads with abrupt Al–Ge heterojunctions. , In contrast to common metal-germanide formation, the Al–Ge exchange results in a single-elemental metallic segment with a low resistivity of ρ = (131 ± 27) × 10 –9 Ωm and an abrupt metal–semiconductor heterostructure without any measurable or electrically active Al impurities within the Ge segment . Further, the Al–Ge contact formation overcomes the difficulty in reproducibility and deterministically defining the phase of the intruded metallic segments as the phase stability of alternative contact materials to nanometer-scale Ge, such as Ni x Ge 1– x and Co x Ge 1– x , is known to exhibit strong variability and yield issues. − Figure a shows a high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) image of the Al–Ge–Al NW heterostructure with a Ge channel length of L Ge = 1.7 μm. High-resolution (HR) TEM images of the Al–Ge junction of the NW heterostructure enwrapped in the 20 nm thick Al 2 O 3 shell and a zoomed-in image of the abrupt Al–Ge interface are shown in Figure b.…”

Formation of ultrathin Ni germanides: solid-phase reaction, morphology and texture

“…Initially, the 2 nm Ni film's morphology is rough upon deposition, as confirmed by STM (not shown). This large roughness is probably due to a combination of the growth of the ε-Ni 5 Ge 3 phase at room temperature, and the Volmer-Weber growth of very thin Ni layers on Ge(1 0 0) [17]. At around 160 °C, the film becomes flatter as the ε-Ni 5 Ge 3 phase continues to grow.…”

Morphology and chemical composition of cobalt germanide islands on Ge(001)

“…In the following, we address the growth of cobalt germanides on Ge(001). In comparison to the Ni-Ge system [8], the Co-Ge system exhibits a more complex bulk phase diagram. As a consequence, it is important to determine and to control which phase is formed under which growth conditions.…”