Ni/GeSn solid-state reaction monitored by combined X-ray diffraction analyses: focus on the Ni-rich phase

Abstract

The Ni/Ge 0.9 Sn 0.1 solid-state reaction was monitored by combining in situ X-ray diffraction, in-plane reciprocal space map measurements and in-plane pole figures. A sequential growth was shown, in which the first phase formed was an Ni-rich phase. Then, at 518 K, the mono-stanogermanide phase Ni(Ge 0.9 Sn 0.1 ) was observed. This phase was stable up to 873 K. Special attention has been given to the nature and the crystallographic orientation of the Ni-rich phase obtained at low temperature. It is demonstrated, with in-plane pole figure measurements and simulation, that it was the "-Ni 5 (Ge 0.9 Sn 0.1 ) 3 metastable phase with a hexagonal structure.

Impact and behavior of Sn during the Ni/GeSn solid-state reaction

“…Although no data about the Ni-Ge-Sn ternary system or the Sn solid solubility in Ni-Ge intermetallics is available in the literature, a hypothesis can be drawn from the observed behavior. The Ni-rich phase was verified to correspond to the " hexagonal phase in the Ni/GeSn system (Quintero et al, 2018b) as for the Ni/Ge system (DeSchutter et al, 2016). This latter is nonstoichiometric and can accept a wide range of Ge concentration between 35 and 44%; a similar behavior is expected for GeSn.…”

“…This shift was linked to stoichiometry variations (i.e. changes in GeSn concentration) in the "-Ni 5 (GeSn) 3 phase (Quintero et al, 2018b). This Nirich phase remained stable until 518 K, at which temperature the Ni(Ge 0.90 Sn 0.10 ) phase was sequentially obtained (see peaks at 34.2, 45.0, 53.9 and 87 ).…”

“…It thus cannot be due to Sn rejection. On the other hand, it is related to stoichiometry variations in the "-Ni 5 [Ge(Sn)] 3 phase (Quintero et al, 2018b). After the shift, the Ni-rich phase remained stable until it was consumed for the formation of the monogermanide or monostanogermanide phase.…”

Texture of NiGe(Sn) on Ge(100) and its evolution with Sn content

“…Different studies have evaluated the crystalline nature of the Ni-rich phase either on GeSn or SiGeSn substrates. The results showed that the Ni-rich phase corresponded to the hexagonal "-Ni 5 Ge 3 metastable phase (De Schutter, Van Stiphout et al, 2016;Quintero et al, 2018c). Meanwhile, in-depth studies concerning the texture of the monostanogermanide phase are not available.…”

“…The possibility of obtaining low resistive values when using nickel makes the contacts a key module to achieve high performance (Vincent et al, 2011;Demeulemeester et al, 2011;Han et al, 2011). Ni/Ge or Ni/GeSn contacts are formed by a solid-state reaction during which Ni 1Àx Ge x or Ni 1Àx (GeSn) x polycrystalline layers are obtained (Balakrisnan et al, 2005;Gaudet et al, 2006;De Schutter, Van Stiphout et al, 2016;van Stiphout et al, 2017;Nishimura et al, 2011;Wirths et al, 2014;Wirths, Geiger et al, 2015;Liu et al, 2015;Quintero et al, 2018c). In order to understand the properties of these polycrystalline films, it is essential to have a good understanding of their microstructure.…”