Negative differential resistance in zigzag-edge graphene nanoribbon junctions

We investigate the transport properties of p(+)/p junctions based on zigzag-edge graphene strips by means of numerical quantum simulation. The p(+) and p domains are created by field effect using appropriate gate electrodes. A negative differential resistance behavior is predicted regardless of the evenness/oddness of the zigzag line number of the ribbon with peak-to-valley current ratio reaching the value of 10 at room temperature. Besides the role of the parity selective rule, the phenomenon is explained as resulting from the suppression of the coherent transition due to the mismatch of modes in the left and right sides of the junction. The influence of various factors governing the peak-to-valley current ratio is analyzed. In particular, it is found that the negative differential resistance may be severely affected by the roughness of ribbon edges.