  We calculate the conductance through double junctions of the type
M(inf.)-Sn-Mm-Sn-M(inf.) and triple junctions of the type
M(inf.)-Sn-Mm-Sn-Mm-Sn-M(inf.), where M(inf.) are semi-infinite metallic
electrodes, Sn are 'n' layers of semiconductor and Mm are 'm' layers of metal
(the same as the electrodes), and compare the results with the conductance
through simple junctions of the type M(inf.)-Sn-M(inf.). The junctions are
bi-dimensional and their parts (electrodes and 'active region') are periodic in
the direction perpendicular to the transport direction. To calculate the
conductance we use the Green's Functions Landauer-B$\ddot{u}$ttiker formalism.
The electronic structure of the junction is modeled by a tight binding
Hamiltonian. For a simple junction we find that the conductance decays
exponentially with semiconductor thickness. For double and triple junctions,
the conductance oscillates with the metal in-between thickness, and presents
peaks for which the conductance is enhanced by 1-4 orders of magnitude. We find
that when there is a conductance peak, the conductance is higher to that
corresponding to a simple junction. The maximum ratio between the conductance
of a double junction and the conductance of a simple junction is 146 %, while
for a triple junction it is 323 %. These oscillations in the conductance are
explained in terms of the energy spectrum of the junction's active region.
