THE TRANSITION FROM A 2-DIMENSIONAL TO A ZERO-DIMENSIONAL ELECTRON-SYSTEM ON SILICON

The dynamic response of a two-dimensional electron system subjected to a lateral superlattice potential of square periodicity is studied via far-infrared transmission spectroscopy on silicon MOS devices with two stacked gates. The bottom gate is a mesh with submicron square periodicity and is isolated from the homogeneous top gate by a layer of SiO2. By independent variation of both gate voltages the superlattice potential strength and the average electron density can be tuned rather independently to study the continuous transition from a homogeneous two-dimensional to a fully confined quasi-zero dimensional electron system. For a moderately density-modulated superlattice we observe two fundamental plasmons reflecting the lowest two reciprocal lattice vectors of the superlattice. With increasing potential modulation these modes exhibit an unexpected softening before merging into a broad absorption band reflecting the strong Landau-damping around the onset of three-dimensional confinement to electron dots.