  Non-reciprocity in the critical current has been observed in a variety of
superconducting systems and has been called the superconducting diode effect.
The origin underlying the effect depends on the symmetry breaking mechanisms at
play. We investigate superconducting micro bridges of NbN and also NbN/magnetic
insulator (MI) hybrids. We observe a large diode efficiency of $\approx$~30\%
when an out-of-plane magnetic field as small as 25~mT is applied. In both NbN
and NbN/MI hybrid, we find that the diode effect vanishes when the magnetic
field is parallel to the sample plane. Our observations are consistent with the
critical current being determined by the vortex surface barrier. Unequal
barriers on the two edges of the superconductor strip result in the diode
effect. Furthermore, the rectification is observed up to a temperature
$\sim$10~K, which makes the device potential for diode based applications over
larger temperature range than before.
