Plasmon excitations and the effects of surface preparation in n-type InAs(001) studied by electron energy loss spectroscopy

High resolution electron energy loss spectroscopy (HREELS) has been used to study the surface plasmon excitations on n-type InAs(001) surfaces prepared either by decapping a protective As layer or by argon ion bombardment and annealing (IBA) procedures. The plasmon frequency for heavily doped decapped samples indicates a free carrier concentration in good agreement with the nominal bulk doping level (n ∼ 5.0 × 1018 cm−3). Subjecting the decapped sample to IBA results in a much higher carrier concentration (∼ 1019 cm−3). Measurements from a lower doped InAs(001) sample (n ∼ 2.0 × 1016 cm−3) prepared by IBA also show an increased carrier concentration (∼ 1018 cm−3), suggesting the presence of additional free carriers as a consequence of the structural damage induced by the sputtering process. For both surface preparations, the plasmon frequency does not vary as a function of the incident electron beam energy and suggests a homogeneous free carrier profile. Measurements of the plasmon frequency as a function of the incident electron beam energy indicate that the depth of electronic damage extends at least 400 Å into the material. The frequency of the surface plasmon is also strongly affected by the ion bombardment and annealing conditions. In particular, the use of high ion beam energies (> 2 keV) directed along the surface normal, gives rise to the highest residual carrier concentrations, consistent with the generation of higher degrees of structural damage in the material.