Black Phosphorus High-Frequency Transistors with Local Contact Bias.

Having a sizable bandgap and high carrier mobility, black phosphorus (BP) is a promising two-dimensional material for high-frequency electronic and optoelectronic devices. Further, for metal-oxide-semiconductor field-effect transistors (MOSFETs) operating at high frequencies, they must have a top gate of submicron length instead of the commonly used global back gate. However, without the global back gate to electrostatically induce doping in BP, top-gated submicron BP MOSFETs have not reached its full potential mainly due to large contact resistances. Here we report top-gated submicron BP MOSFETs with local contact bias electrodes to induce doping in the contact region. This resulted in reduced contact resistance and, in turn, orders-of-magnitude improvement in current capacity (> 500 μA/μm) and peak transconductance (> 40 μS/μm), if compared with top-gated BP transistors without any back-gating scheme. In turn, these improvements resulted in a forward current-gain cutoff frequency of 37 GHz and a maximum frequency of oscillation of 22 GHz at room temperature, the highest reported for BP MOSFETs up to date.