Crystal Phases in Hybrid Metal-Semiconductor Nanowire Devices

We investigate the metallic phases observed in hybrid metal-GaAs nanowire devices obtained by controlled thermal annealing of Ni/Au electrodes. Devices are fabricated onto a SiN membrane compatible with transmission electron microscopy studies. Energy dispersive X-ray spectroscopy allows us to show that the nanowire body includes two Ni-rich phases that thanks to an innovative use of electron diffraction tomography can be unambiguously identified as Ni₃GaAs and Ni₅As₂ crystals. The mechanisms of Ni incorporation leading to the observed phenomenology are discussed.