  We report quantum dots fabricated on very shallow 2-dimensional electron
gases, only 30 nm below the surface, in undoped GaAs/AlGaAs heterostructures
grown by molecular beam epitaxy. Due to the absence of dopants, an improvement
of more than one order of magnitude in mobility (at 2E11 /cm^2) with respect to
doped heterostructures with similar depths is observed. These undoped wafers
can easily be gated with surface metallic gates patterned by e-beam
lithography, as demonstrated here from single-level transport through a quantum
dot showing large charging energies (up to 1.75 meV) and excited state energies
(up to 0.5 meV).

Mesoscale and Nanoscale Physics