Surface transfer doping induced effective modulation on ambipolar characteristics of few-layer black phosphorus

Black phosphorus, a fast emerging two-dimensional material, has been configured as field effect transistors, showing a hole-transport-dominated ambipolar characteristic. Here we report an effective modulation on ambipolar characteristics of few-layer black phosphorus transistors through in situ surface functionalization with caesium carbonate (Cs 2 CO 3 ) and molybdenum trioxide (MoO 3 ), respectively. Cs 2 CO 3 is found to strongly electron dope black phosphorus. The electron mobility of black phosphorus is significantly enhanced to ~27 cm 2 V −1 s −1 after 10 nm Cs 2 CO 3 modification, indicating a greatly improved electron-transport behaviour. In contrast, MoO 3 decoration demonstrates a giant hole-doping effect. In situ photoelectron spectroscopy characterization reveals significant surface charge transfer occurring at the dopants/black phosphorus interfaces. Moreover, the surface-doped black phosphorus devices exhibit a largely enhanced photodetection behaviour. Our findings coupled with the tunable nature of the surface transfer doping scheme ensure black phosphorus as a promising candidate for further complementary logic electronics.