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.