  Phosphorene is emerging as a promising 2D semiconducting material with a
direct band gap and high carrier mobility. In this paper, we examine the role
of the extrinsic point defects including surface adatoms in modifying the
electronic properties of phosphorene using density functional theory. The
surface adatoms considered are B, C, N, O and F with a [He] core electronic
configuration. Our calculations show that B and C, with electronegativity close
to P, prefer to break the sp3 bonds of phosphorene, and reside at the
interstitial sites in the 2D lattice by forming sp2 bonds with the native
atoms. On the other hand, N, O and F, which are more electronegative than P,
prefer the surface sites by attracting the lone pairs of phosphorene. B, N and
F adsorption will also introduce local magnetic moment to the lattice.
Moreover, B, C, N and F adatoms will modify the band gap of phosphorene
yielding metallic transverse tunneling characters. Oxygen does not modify the
band gap of phosphorene, and a diode like tunneling behavior is observed. Our
results therefore offer a possible route to tailor the electronic and magnetic
properties of phosphorene by the adatom functionalization, and provide the
physical insights of the environmental sensitivity of phosphorene, which will
be helpful to experimentalists in evaluating the performance and aging effects
of phosphorene-based electronic devices.
