Tunable transport and optoelectronic properties of monolayer black phosphorus by grafting PdCl2 quantum dots

Abstract

The electronic, transport, and optoelectronic properties of monolayer black phosphorus (MLBP) are much influenced by grafting PdCl₂ groups, demonstrated here by using density functional theory (DFT) and non-equilibrium Green's function (NEGF) as well as the Keldysh Nonequilibrium Green's Functions (KNEGF) methods. We find that the PdCl₂ groups prefer to locate over the furrow site of MLBP and form a planar quadridentate structure of . The PdCl₂ groups serve as quantum dots by introducing discrete flat levels between the MLBP valence band and the Fermi level (E_f). The conductivity is much lowered after attaching PdCl₂ quantum dots, due to the fact that the scattering effect of PdCl₂ plays a major role in the process of electron transporting. A threshold voltage is found for the functionalized system with a large density of PdCl₂ quantum dots, a valuable clue for exploring current switches. However, no evident threshold voltage is found for the pure MLBP. Electrons permeate easier through the armchair direction compared with the zigzag either in the pure MLBP or in the functionalized composites. More importantly, grafting PdCl₂ quantum dots is very beneficial for enhancing photoresponse. The values of photoresponse for the modified species are about 20 times higher than the free MLBP. A significant photoresponse anisotropy is observed for both MLBP and nPdCl₂-BP (n = 1, 2, and 4), contrary to the conductivity, the zigzag direction shows much stronger photoresponse than the armchair. All of the aforementioned unique properties make these new two-dimensional (2D) MLBP based materials especially attractive for both electronic and optoelectronic devices.