We review some electron transport experiments on few-electron,
vertical quantum dot devices. The measurement of current versus
source-drain voltage and gate voltage is used as a
spectroscopic tool to investigate the energy characteristics of interacting
electrons confined to a small region in a semiconducting
material. Three energy scales are distinguished: the
single-particle states, which are discrete due to the
confinement involved; the direct Coulomb interaction between electron
charges on the dot; and the exchange interaction between electrons
with parallel spins. To disentangle these energies, a magnetic
field is used to reorganize the occupation of electrons over the
single-particle states and to induce changes in the spin states.
We discuss the interactions between small numbers of electrons
(between 1 and 20) using the simplest possible models.
Nevertheless, these models consistently describe a large set of
experiments. Some of the observations resemble similar
phenomena in atomic physics, such as shell structure and periodic
table characteristics, Hund's rule, and spin singlet and triplet states. The
experimental control, however, is much larger than for atoms: with one device all the artificial elements can be studied by adding electrons to the quantum dot when changing the gate voltage.
