Photogating-Induced Controlled Electrical Response in 2D Black Phosphorus

Photo-induced tunability in charge carriers can be proven as a promising alternative approach to traditional electrostatic gating because of its flexibility to operate in noncontact mode. We have established a reversibly tunable optical gating technique on a few-layer black phosphorus (BP) flake by shining a laser beam, with variation in incident power and energy. The laser power-dependent evolution of Raman spectra of the BP flake is compared with the effect of conventional electrostatic gating. The comparison shows identical linear redshift in characteristic vibrational modes; thereby, a correlation between the laser power and induced charge carrier density is established. The transfer characteristics of BP field effect transistor (FET) under varying laser power validate the optical tunability of the gating effect and demonstrate identical variation in charge carrier density, found in conventional back-gated BP FET.