  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.
