  In this work, we study the electronic and transport properties of phosphorene
nanorings in two perpendicular directions (zigzag and armchair directions) in
the presence of zigzag metallic source and drain leads. Our results are based
on the non-equilibrium Green's function (NEGF) method and a five-parameter
tight-binding (TB) approach. We investigate how system parameters affect the
electronic transport. These parameters include the radius of the rings, the
width of the leads and the external potential. Our results show that for all
configurations studied, a transport energy gap exists whose width can be tuned
by the width of the leads and the radius of the nanoring. The transmission
function of wider leads shows more sensitivity to the variation of the inner
radius due to higher electronic states that can respond to smaller changes in
the scattering region. In addition, the transport along the armchair direction
is more susceptible to tuning than the transport along the zigzag direction.
The effects of external potentials on the conductance are more pronounced than
the geometrical parameters. In particular the circular potential of the
amplitude of 0.1 eV can widen the transport gap by about ~0.35 eV.
