  We calculate the current-voltage (I-V) relation for planar superconducting
d-wave junctions for both arbitrary transmission of the junction and arbitrary
orientation of the d-wave superconductors. The midgap states (MGS) present at
interfaces/surfaces of a d-wave superconductor influence the I-V relation. In
some arrangements we find considerable negative differential conductance and
lower threshold voltage for non-zero current due to resonant conduction through
MGS.
