Impact of metal contact depth on device performance in back-gated semiconductor nanowire field effect transistors

Self assembled semiconductor (e.g. silicon, germanium) nanowires represent an attractive platform to fabricate field effect transistors devices that can reduce short channel effects in by comparison planar devices. Back-gated field effect transistors with metal contacts represent a common device fabrication method employed to test the electronic properties of semiconductor nanowires. Using a systematic electrical characterization study of back-gated germanium nanowire device with nickel (Ni) contacts, here we show experimentally and theoretically that the metal contact depth, controlled by annealing the device at moderate temperatures, critically impacts the device performance. Interestingly, as the metal contact diffuses into the nanowire during annealing, the device current shows a non monotonic dependence as function of the metal contact penetration depth.