Plasmon excitations and accumulation layers in heavily doped InAs(001)

High-resolution electron-energy-loss spectroscopy (HREELS) has been used to study the (001) surface of degenerate n-type InAs grown by molecular-beam epitaxy and prepared either by As decapping or ion bombardment and annealing (IBA). The effects of temperature on the conduction-band electron plasmon excitation have been monitored with HREELS, and analyzed using dielectric theory in the framework of a three-layer model consisting of the bulk, an accumulation layer, and a carrier-free layer at the surface. Specific emphasis has been placed on the importance of the individual layer thicknesses, spatial dispersion, and plasmon lifetime in obtaining good theoretical agreement with the experimental spectra. The measured plasmon spatial dispersion coefficient for the decapped samples was found to agree with the predictions of the Thomas-Fermi model, but was significantly reduced for samples prepared by IBA. This is interpreted as a reduction in the average carrier velocity due to additional defect scattering. Samples prepared by both methods showed a sharp increase in plasmon damping at short wavelengths which is attributed to Landau damping. Ohmic damping of the plasmon at long wavelengths was found to be greater in the ion-bombarded samples, again due to additional defect scattering. IBA was also shown to increase the carrier concentration through the creation of donorlike defects. Neither the surface-state energy nor the surface-state density were found to be significantly affected by the IBA treatment.