Plasmons in spatially non-uniform magnetic fields

A non-planar two-dimensional electron gas (2DEG) has been realised by using molecular beam epitaxy to grow a high mobility heterostructure on a (1 0 0) n(+)-GaAs layer selectively etched to create a two-dimensional array of cavities through the n(+)-GaAs which are bounded by higher-index facets. Far-infrared (FIR) cyclotron resonance spectra show one absorption mode associated with an electron gas formed inside the cavities and confined in both lateral directions. Typical confinement energies of 23 cm(-1) and widths of 1000 nm are derived from the FIR spectra and magneto resistance measurements. A second mode occurs at a frequency lower than that measured for a planar 2DEG. Its origin is discussed in terms of magneto-plasmons excited across a non-planar region of the electron gas in a spatially non-uniform magnetic field. Combining this information with atomic force microscopy images provides a comprehensive picture of the nature of the lateral confinement in this structure. (C) 1998 Elsevier Science B.V. All rights reserved.