  The conditions necessary for a nanotube junction connecting a metallic and
semiconducting nanotube to rectify the current are theoretically investigated.
A tight binding model is used for the analysis, which includes the Hartree-Fock
approximation and the Green's function method.
  It is found that the junction has a behavior similar to the backward diode if
the gate electrode is located nearby and the Fermi level of the semiconducting
tube is near the gap.
  Such a junction would be advantageous since the required length for the
rectification could be reduced.
