Engineering the Electronic Structure of Black Phosphorus

There are rapidly growing interests in the study of two-dimensional (2D) atomic crystals owing to promising device characteristics that may impact our future electronics technology. A key issue is controlling their electronic states to overcome the limit of natural properties. Black phosphorus, consisting of 2D phosphorene layers, has been widely predicted to have a tunable band structure with external perturbations, such as strain and electric field. In this talk, I will introduce angle-resolved photoemission spectroscopy studies on the band evolution of black phosphorus by surface doping. The in-situ deposition of alkali-metal atoms induces 2D electron gas confined in few surface phosphorene layers. The vertical electric field from dopants modulates the band gap and tunes the material from a narrow-gap semiconductor to a band-overlapped semimetal. At the critical density of this semiconductor-semimetal transition, the system becomes a 2D Dirac semimetal whose band dispersion is highly anisotropic, linear in armchair and quadratic in zigzag directions.