Tunable metal contacts at layered black-arsenic/metal interface forming during metal deposition for device fabrication

Understanding the kinetics of interfacial reaction in the deposition of metal contacts on 2D materials is important for determining the level of contact tenability and the nature of the contact itself. Here, we find that some metals, when deposited onto layered black-arsenic films using e-beam evaporation, form a-few-nm thick distinct intermetallic layer and significantly change the nature of the metal contact. In the case of nickel, the intermetallic layer is Ni11As8, whereas in the cases of chromium and titanium they are CrAs and a-Ti3As, respectively, with their unique structural and electronic properties. We also find that temperature, which affects interatomic diffusion and interfacial reaction kinetics, can be used to control the thickness and crystallinity of the interfacial layer. In the field effect transistors with black-arsenic channel, due to the specifics of its formation, this interfacial layer introduces a second and more efficient edge-type charge transfer pathway from the metal into the black-arsenic. Such tunable interfacial metal contacts could provide new pathways for engineering highly efficient devices and device architectures. In 2D materials devices, understanding interfacial reactions in the formation of metal contacts is important for tuning their properties. Here, electron microscopy reveals the formation of an intermetallic contact layer, characterized by an efficient edge-type charge transfer, when nickel, chromium, or titanium is deposited onto black-arsenic films.