Degradation pattern of black phosphorus multilayer field−effect transistors in ambient conditions: Strategy for contact resistance engineering in BP transistors

Black phosphorus (BP) has been proposed as a future optoelectronic material owing to its direct bandgap with excellent electrical performances. However, oxygen (O ₂ ) and water (H ₂ O) molecules in an ambient condition can create undesired bubbles on the surface of the BP, resulting in hampering its excellent intrinsic properties. Here, we report the electrical degradation pattern of a mechanically exfoliated BP field–effect transistor (FET) in terms of the channel and contact, separately. Various electrical parameters such as the threshold voltage (V _TH ), carrier mobility (μ), contact resistance (R _CT ) and channel resistance (R _CH ) are estimated by the Y function method (YFM) with respect to time (up to 2000 min). It is found that R _CT reduces and then, increases with time; whereas, the behavior of R _CH is vice versa in ambient conditions. We attribute these effects to oxygen doping at the contact and the surface oxidation effects on the surface of the BP, respectively.