Surface modes in accumulation layers

Abstract

We study the coupled modes of plasmons and optical phonons near a surface accumulation layer on an ionic semiconductor. Using a simple model geometry the number, dispersion, and external electronic coupling of surface collective modes are described. Several model calculations are presented to illustrate these properties. Various limiting cases allow comparison with earlier work. We identify the analogs within our model of plasmarons and subband excitations. A new set of surface modes is described, whose frequencies lie in the phonon range but whose existence requires spatial dispersion in the plasmon response. Their observation in electron-energy-loss spectra should be possible.