  The effects of lattice distortion and chemical disorder on charge transport
properties of two-terminal zigzag phosphorene nanoribbons (zPNRs), which shows
resonant tunneling behavior under an electrical applied bias, are studied. Our
comprehensive study is based on an {\it ab~initio} quantum transport
calculations on the basis of the Landauer theory. We use nitrogen and silicon
substitutional dopant atoms, and employ different physical quantities such as
$I-V$ curve, voltage drop behavior, transmission spectrum, transmission
pathway, and atomic current, to explore the transport mechanism of zPNR devices
under a bias voltage. The calculated transmission pathways show the transition
from a ballistic transport regime to a diffusive and in some particular cases
to localized transport regimes. Current flowing via the chemical bonds and
hopping are monitored, however, the conductance originates mainly from a charge
traveling through the chemical bonds in the vicinity of the zigzag edges. Our
results show that, in the doped systems, the device conductance decreases and
negative differential resistance characteristic becomes weak or eliminates.
Besides, the conductance in a pure zPNR system is almost independent of the
ribbon width.
