  Achieving good quality Ohmic contacts to van der Waals materials is a
challenge, since at the interface between metal and van der Waals material,
different conditions can occur, ranging from the presence of a large energy
barrier between the two materials to the metallization of the layered material
below the contacts. In black phosphorus (bP), a further challenge is its high
reactivity to oxygen and moisture, since the presence of uncontrolled oxidation
can substantially change the behavior of the contacts. In this study, we
investigate the influence of the metal used for the contacts to bP against the
variability between different flakes and different samples, using three of the
most used metals as contacts: Chromium, Titanium, and Nickel. Using the
transfer length method, from an analysis of ten devices, both at room
temperature and at low temperature, Ni results to be the best metal for Ohmic
contacts to bP, providing the lowest contact resistance and minimum scattering
between different devices. Moreover, we investigate the gate dependence of the
current-voltage characteristics of these devices. In the accumulation regime,
we observe good linearity for all metals investigated.
