Thickness Effect on the Solid-State Reaction of a Ni/GaAs System.

Ni thin films with different thicknesses were grown on a GaAs substrate using the magnetron sputtering technique followed by in situ X-ray diffraction (XRD) annealing in order to study the solid-state reaction between Ni and GaAs substrate. The thickness dependence on the formation of the intermetallic phases was investigated using in situ and ex situ XRD, pole figures, and atom probe tomography (APT). The results indicate that the 20 nm-thick Ni film exhibits an epitaxial relation with the GaAs substrate, which is (001) Ni//(001) GaAs and [111] Ni//[110] GaAs after deposition. Increasing the film's thickness results in a change of the Ni film's texture. This difference has an impact on the formation temperature of NiGaAs. This temperature decreases simultaneously with the thickness increase. This is due to the coherent/incoherent nature of the initial Ni/GaAs interface. The NiGaAs phase decomposes into the binary and ternary compounds xNiAs and NiGaAs at about 400 °C. Similarly to NiGaAs, the decomposition temperature of the second phase also depends on the initial thickness of the Ni layer.