Infrared absorption by coupled surface-phonon-surface-plasmon modes in small GaAs crystals

Abstract

The infrared transmission spectra of small GaAs crystals (0.5 mu m in average size) are reported. The samples are produced by mechanical grinding down from the bulk crystals with known carrier concentrations from 5.3*10-17 to 2.4*1018 cm-3. The spectrum is constructed from a surface phonon mode and coupled modes between surface phonons and plasmons. The two coupled modes are clearly separated and their frequencies agree very well with the theoretical dispersion curves. On the basis of the theory of an average dielectric function the observed spectra are reproduced from the calculations, in which the particle is assumed to be a sphere composed of a shell with no carriers and a core containing high carrier concentration.