Fabrication of undoped AlGaAs/GaAs electron quantum dots
  We have fabricated a quantum dot single electron transistor based on an AlGaAs/GaAs heterostructure without any modulation doping. Our device is very stable from an electronic perspective, with clear Coulomb blockade oscillations, and minimal drift in conductance when the device is set to the midpoint of a Coulomb blockade peak and held at constant gate bias. Bias spectroscopy measurements show typical Coulomb 'diamonds' free of any significant charge fluctuation noise. We also observe excited state transport in our device. 
Andrew M. See, Oleh Klochan, Adam P. Micolich, Alex R. Hamilton,   Martin. Aagesen and Poul Erik Lindelof
cond-mat.mes-hall