From two-dimensional to three-dimensional quantum dots

Laterally defined quantum dot structures have been fabricated on the basis of AlxGa1−xAs parabolic quantum wells which allow the occupation of more than one subband in growth direction. Magneto-Coulomb oscillations allow the determination of a gate parameter regime where the states of the second subband are occupied in the quantum dot. The occupation of the second subband in the dot comes along with fluctuations in the conductance peaks at zero magnetic field which we characterize with time dependent measurements. We discuss the possibility that the fluctuations are an intrinsic property of the dot at the threshhold to two occupied subbands.