  We report on systematic study of electronic transport in low-biased,
disordered graphene nanowires. We reveal the emergence of unipolar transport as
the defect concentration increases beyond 0.3\% where an almost insulating
behaviour is observed on n-type channels whilst a metallic behaviour is
observed in p-type channels. The conductance shows a plateau that extends
through the entire side above the Dirac point (n-type) and the conductivity
coincides with the minimum conductivity at the Dirac point. The minimum
conductivity decreases with increasing defect concentration pointing out
towards the absence of zero energy modes in the disordered samples. Raman
spectroscopy and X-ray photoemission spectroscopy were used to probe the nature
of the defects created by helium ion irradiation and revealed the presence of
oxygen-carbon bonds as well as the presence of $sp^3$ configuration uncovered
from the C KLL Auger spectrum. The observed behaviour is attributed to the
dangling bonds created by sputtering of carbon atoms in graphene lattice by
bombarding helium ions. The dangling bonds act as charge traps, pinning the
Fermi level to the Dirac point.
