  A few-electron double quantum dot was fabricated using
metal-oxide-semiconductor(MOS)-compatible technology and low-temperature
transport measurements were performed to study the energy spectrum of the
device. The double dot structure is electrically tunable, enabling the
inter-dot coupling to be adjusted over a wide range, as observed in the charge
stability diagram. Resonant single-electron tunneling through ground and
excited states of the double dot was clearly observed in bias spectroscopy
measurements.
