In this work we calculate the I-V characteristics of quantum dot devic
es. The I-V curves of such structures are dependent not only upon the
dot spectrum, but also on whether they are connected to bulk contacts
or to contacts confined in one or more direction. Here we concentrate
on 1D-0D-1D and 3D-0D-3D devices, using two different techniques: a tr
ansfer-matrix approach and a non-equilibrium Green's function formalis
m. The Coulomb interaction and single particle aspects are included in
the theory. For 1D-0D-1D structures the I-V curve consists of a serie
s of upward and downward steps, the latter being present only if the C
oulomb repulsion inside the dot is important. These downward steps pro
ve to be thermally robust. For 3D-0D-3D devices the I-V curve is domin
ated by peaks rather than steps, reflecting the difference in density
of states in the contacts. Comparison with experiments shows very good
agreement.