The excitation of magnetoplasmons in Al Gaz As-GaAs quantum dots and wires with farinfrared transmission spectroscopy is investigated. An interaction of the magnetoplasmon resonance with harmonics of the cyclotron resonance nu, (n = 2, 3) is observed. Results of self-consistent calculations of the magnetoplasmon dispersion show similar effects when the lateral confinement of the electrons has a slight deviation from a parabolic form. Comparison of the results indicates a good qualitative agreement between experiments and models. I. INTR.ODU CTIONProgress in submicrometer technology and the ability to tailor potentials and interactions has triggered a broad activity in low-dimensional semiconductor microstructures, in particular quantum wires and dots. These systems can be fabricated starting from two-dimensional electron systems (2DES's), for example in Al Gai AsGaAs heterostructures. In a 2DES, the electronic motion is quantized in one direction (labeled z in the following).With additional lateral potentials in the y or both the x and the y direction one can realize, respectively, quantum wires with quantized energy levels for the y direction and a free dispersion in the x direction or quantum dots with a totally quantized energy spectrum.In this paper we focus our attention on modulationdoped systems. Then the most direct information on the system can be derived from far-infrared (FIR) spectroscopy where one excites the electrons into higher states. In fact quite a number of FIR investigations on quantum wires and dots have been performed, (for a review, see Ref. 10). In particular it was possible to realize dots with well defined small number of electrons N, = 1, 2, 3.. . . For these systems, so-called quantumdot atoms, one would expect, similarly as for real atoms, a rich absorption spectrum with many lines. The experimental spectra, however, were very simple. For dots only, one resonance is observed at B = 0, which splits with increasing B into two modes, independent of the number of electrons per dot (see below). The explanation for this behavior is that for electrostatic reasons modulation-doped quantum wires and dots have a nearly perfect parabolic lateral confinement potential. In this case, the generalized Kohn theorem applies, which states that with dipole excitation only a rigid center-ofmass motion of all the electrons can be excited and no information on relative motion and internal degrees of freedom can be achieved.With further progress of technology it was possible to create potentials with deviations from the parabolic shape and actually observe various kinds of internal motion. For example, steps in the B dispersion of quantum wires related to the depopulation of one-dimensional (1D) subbands iri a magnetic field have been found. In dots with a quadratic shape, higher modes and anticrossing of modes have been observed. Also, an energy splitting associated with the transition from the singlet to the triplet state in a quantum-dot helium, a quantum dot with two electrons, has been discussed.In va...

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Three-dimensional arrays of vertically stacked sidewall quantum wires are fabricated by molecular beam epitaxy on GaAs (311)A substrates patterned with 500-nm-pitch gratings. The cathodoluminescence spectra at low temperature are dominated by the emission from the quantum wires with narrow linewidth accompanied by a very weak emission from the connecting thin quantum wells due to localization of excitons at random interface fluctuations. When the carriers in the quantum well become delocalized at elevated temperature, only the strong emission from the quantum-wire array is observed revealing perfect carrier capture into the quantum wires without detectable thermal repopulation of the quantum well up to room temperature. Thus, unpreceded device quality of this quantum-wire structure is demonstrated.