Geometrical-induced rectification in two-dimensional ballistic   nanodevices
  The paper demonstrates that a two-dimensional ballistic nanodevice in which the electron gas satisfies either the Schroodinger equation (as in quantum wells in common semiconductor heterostructures) or the Dirac equation (as in graphene) is able to rectify an electric signal if the device has a non-uniform cross section, for instance a taper configuration. No p-n junctions or dissimilar electrodes are necessary for rectification. 
Daniela Dragoman and Mircea Dragoman
cond-mat.mes-hall