Angular dispersion of Fuchs–Kliewer modes on GaAs(100) by digital high‐resolution electron energy‐loss spectroscopy

High‐resolution electron energy‐loss spectroscopy has been used to study surface phonon and surface plasmon excitations of GaAs (100). The angular dispersion (energy loss versus electron beam incidence angle) of Fuchs–Kliewer surface optical phonons and free‐carrier surface plasmons of GaAs(100) have been determined with an experimental resolution of 10 meV. Theoretical dispersion relations were calculated for these samples using the Lindhard dielectric function and assuming that only the surface loss function is measured. Phonon loss and gain peaks were observed which decreased in intensity with increasing momentum parallel to the surface q_∥, as expected for dipole selection rules. The plasmon loss features seemed to decrease less rapidly with q_∥ than the phonon peaks. Experimental peaks positions are described reasonably well by the two coupled modes that result from the theoretical model with an effective surface carrier density of 6×10¹⁸ cm⁻³ which is (1)/(3) that of the bulk.