QUANTUM DOTS IN TILTED MAGNETIC-FIELDS

Arrays of field-effect confined quantum dots with diameters down to 100 nm have been prepared from AlxGa1-xAs/GaAs heterostructures. In far-infrared spectroscopy, transitions are induced between the 2-3 meV separated quantum levels of the lateral confinement. In tilted magnetic fields B, we observe a resonant coupling to states arising from the confinement in the growth direction. The level spacing in this z-direction is found to be only a few meV in our samples and thus comparable to the level spacing of the lateral confinement. The excitation spectrum that we observe is determined by the total magnetic field B. Thus the quantum dots are essentially three-dimensional objects. We observe a similar transition to a three-dimensional behavior in two-dimensional electron gases with small subband spacings.