Since high-performance field-effect transistors (FETs) were first fabricated based on few-layer black phosphorus in 2014, 1 the potential applications of black phosphorus in electronics began to attract extensive attention. It is well known that the preferred channel materials for constructing sub-10 nm transistors should present two essentials, ultrathin body and high carrier mobility. A thinner body of the conducting channel may lead to better gate electrostatics and controllability, which would be propitious to minimize the short-channel effect during the scaling down of FETs’ dimensions. Higher carrier mobility promises higher speed operation of FETs with fixed dimension (channel length). However, compromise between thin body and high mobility is inevitable in conventional bulk semiconductors, in which the carrier mobility is severely degraded when the body is thinned to several nanometers. The emerging 2D materials, including graphene and transition metal dichalcogenides, have demonstrated their advantages for constructing sub-10 nm FETs 2-4 owing to their ultrathin body without obvious carrier degradation. Unfortunately, these famous 2162D materials suffer from intrinsic deficiency and are therefore considered unsuitable for constructing high-performance FETs.

For example, graphene is famous for its ultrahigh mobility and atomic thickness, but the lack of bandgap results in no switching off or current saturation in graphene transistors, which limit its application in digital and logic circuits. 2, 5 Transition metal dichalcogenides like MoS2 and WSe2 have a bandgap larger than 1 eV. However, transition metal dichalcogenides always suffer from low carrier mobility 6-9 and are not fit for high-performance applications in electronics. Black phosphorus (BP), presenting both a relatively large bandgap and high mobility, has drawn much attention recently as a new 2D semiconducting material. Layered like graphene, the phosphorus atom is covalently bonded with three neighboring atoms in each layer, with weak Van der Waals forces holding the layers together. The puckered layers in black phosphorus should lead to a bandgap of ∼2 eV 10, 11 for a monolayer and ∼0.3 eV for the bulk. 12, 13 Moreover, BP presents high mobility up to 200–3000 cm2/V s, which is much larger than that of transition metal dichalcogenides. The combination of high mobility and layer-dependent bandgap makes BP one of the most attractive 2D materials for nanoelectronics and optoelectronics. 14-18