We systematically explore chemical functionalization of monolayer black phosphorene via chemisorption of oxygen and fluorine atoms. Using the cluster expansion technique, with vary- ing concentration of the adsorbate, we determine the ground states c
onsidering both single- as well as double- side chemisorption, which have novel chemical and electronic properties. The nature of the bandgap depends on the concentration of the adsorbate: for fluorination the direct bandgap first decreases, and then increases while becoming indirect, with increasing fluorination, while for oxidation the bandgap first increases and then decreases, while mostly maintaining its direct nature. Further we find that the unique anisotropic free-carrier effective mass for both the electrons and holes, can be changed and even rotated by 90 degrees, with controlled chemisorption, which can be useful for exploring unusual quantum Hall effect, and novel electronic devices based on phosphorene.
We investigate the possibility of band structure engineering in the recently predicted 2D layered form of blue phosphorus via an electric field (E$_z$) applied perpendicular to the layer(s). Using density functional theory, we study the effect of a t
ransverse electric field in monolayer, as well as three differently stacked bilayer structures of blue phosphorus. We find that, for E$_z > 0.2$ V/AA the direct energy gap at the $Gamma$ point, which is much larger than the default indirect band gap of mono- and bilayer blue phosphorus, decreases linearly with the increasing electric field; becomes comparable to the default indirect band gap at E$_z approx 0.45 (0.35)$ V/AA for monolayer (bilayers) and decreases further until the semiconductor to metal transition of 2D blue phosphorus takes place at E$_zapprox 0.7 (0.5)$ V/AA for monolayer (bilayers). Calculated values of the electron and hole effective masses along various high symmetry directions in the reciprocal lattice suggests that the mobility of charge carriers is also influenced by the applied electric field.
