Plasmons in lateral-surface superlattices with periodically structured interfaces under normally applied electric fields.

Abstract

The intrasubband plasmons in the long-wavelength limit and intersubband plasmons in the zero-wave-vector limit are calculated numerically for the GaAs/AlAs lateral-surface superlattices (LSSL's) with periodically structured interfaces and short lateral periods under normally applied electric fields. Square-root dispersion relations are found for the intrasubband plasmons with the in-plane wave vector \ensuremath{\Vert}${\mathit{q}}_{\mathit{z}}$\ensuremath{\Vert}\ensuremath{\ll}1 and ${\mathit{q}}_{\mathit{y}}$=0. The frequencies of the intrasubband plasmons in the LSSL's are expected to be less than those of plasmons in quantum wells with the same electron densities. Oscillations of the intrasubband-plasmon frequencies as functions of the Fermi level, or equivalently the electron density, are predicted. A sensitive dependence of the intrasubband-plasmon frequencies on the electric fields applied normally to the LSSL's is found, a result that is absent in quantum wells with planar interfaces. The energies of the intersubband plasmons are found to be close to the single-electron transition energies between the two lowest subbands at the center of the first Brillouin zone (FBZ) for the LSSL's with small interface structures and short lateral periods, typically with ${\mathit{L}}_{\mathit{x}}$200 \AA{} for the LSSL's we considered. The effects of the electron Coulomb interactions on the optical absorptions of the LSSL's are negligible. The optical absorptions of the LSSL's are dominated by the single-electron transitions across the first subband gap at the edge of the FBZ, if the electron densities are high enough to move the Fermi level into the first subband gaps of the LSSL's. Distinctive and strong intersubband-plasmon-absorption peaks appear in the optical-absorption spectra if the lateral periods of the LSSL's increase, typically if ${\mathit{L}}_{\mathit{x}}$>400 \AA{} for the LSSL's we considered. The changes of the intersubband-plasmon energies as functions of the interface structures, electron densities, lateral periods of the LSSL's, and electric fields applied normally to the LSSL's are investigated.