Ultraclean surface restoration and giant photoresponse enhancement of violet phosphorus

Violet phosphorus (VP), a recently developed kind of layered material, features exotic in-plane anisotropy, alluring thickness-dependent bandgap, and better thermal stability than its phosphorus allotropes. Such a broad variety of functionalities indicates VP is a promising candidate for advanced nanophotonics. However, its hydrophilic surface-induced air instability hinders further exploration and extensive device integration for photodetection and beyond. Herein, we report the successful restoration of the clean VP surfaces through nitrogen plasma combined with vacuum thermal annealing. Via manipulation of plasma excitation power, we can also achieve thickness etching and nondestructive p-doping to VP, paving the way for fabrication and engineering of VP photodetectors. As a proof-of-concept, plasma-treated VP photodetectors have been fabricated. Stemming from the plasma treatment-induced p-doping and hole trapping centers, the VP photodetectors exhibit giant photoresponse enhancement, reaching a high responsivity of 1.923 A/W, and is dramatically improved by 1300% compared with that before plasma treatments, which envisions high-sensitivity photodetection for next-generation more-than-Moore optoelectronics.