Surface Functionalization of Black Phosphorus by Cu: Effective Electron Doping and Enhanced Photoresponse

Black phosphorus (BP) emerges as a monoelemental 2D semiconductor with a direct bandgap, exhibiting a hole-dominated ambipolar transport characteristic. The modulation of charge carriers type and concentration is of great necessity for its applications in electronic and optoelectronic devices. Herein, the effective electron doping of BP by surface functionalization of copper (Cu) is demonstrated. Moreover, the electron mobility of BP increases from 63 to 156 cm2 V−1 s−1 after Cu modification. The formation of electron accumulation layer within BP after Cu modification is further revealed by in situ photoelectron spectroscopy characterizations. No chemical reaction is observed at the Cu/BP interface where a notable electron transfer from Cu to BP occurs indicated by an ≈0.20 eV shift of P 2p peak to high binding energy after Cu functionalization. With the formation of local electric field at the interface, the dissociation of photogenerated excitons is facilitated, leading to an ≈6 times enhancement of the photoresponse for Cu-modified BP.