Search

Ni-GeSn based materials are promising in order to obtain contacts in complementary metal oxide semiconductor and Si photonic devices. In this work, a systematic and comprehensive study of the solid-state reaction between NiPt thin films and Ge0.9Sn0.1 layers is carried out. A particular focus is given on the impact of the addition of 10 at. % of Pt in Ni thin films. In situ X-ray diffraction and in-plane reciprocal space map measurements reveal a sequential growth in which the first phase appearing corresponds to a Ni-rich phase: (Ni0.9Pt0.1)5(Ge0.9Sn0.1)3. Then, at 245 °C, the Ni-rich phase vanishes to the benefit of the mono-stanogermanide phase (Ni0.9Pt0.1)(Ge0.9Sn0.1), which is unstable. At 360 °C, a more stable (Ni1– yPty)(Ge1– xSnx) phase is obtained concomitantly to the formation of PtSnx compounds. Finally, Sn segregation occurs at even higher temperatures. Even if Pt addition in Ni thin films complicates the phase formation sequence, it positively impacts the surface morphology and roughness, delays film agglomeration and Sn segregation, and stabilizes the electrical properties of the stanogermanide in a wide range of temperatures.

Thin films of Ni(Si1−xGex) are of interest for their applications in metal-oxide semiconductor transistors as contacts and interconnections. In this work, the lattice parameters and the coefficients of linear thermal expansion (γa, γb, and γc) of the orthorhombic Ni(Si1−xGex) alloys, with 0⩽x⩽1, were determined from high-temperature x-ray diffraction data (298–1073K). A negative thermal expansion along the b axis of Ni(Si1−xGex) is observed for all x values of the Ge concentration: the magnitude of the thermal expansion coefficient decreases with increasing Ge concentration. The anisotropy of the thermal expansion is potentially important for the integration of Ni(Si1−xGex) in microelectronic devices.

The reaction between nanometric Ni films and Ge is analyzed using isothermal x-ray diffraction measurements and transmission electron microscopy. It is found that NiGe is formed during deposition at room temperature. The metal rich phase that grows during heat treatment has been clearly identified to be Ni5Ge3. The simultaneous growths of Ni5Ge3 and NiGe have been observed on amorphous and polycrystalline germanium. This is in contrast with the usual sequential growth reported in thin films.