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 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 similar to 5.0x10(18) cm(-3)). Subjecting the decapped sample to IBA results in a much higher carrier concentration (similar to 10(19) cm(-3)). Measurements from a lower doped InAs(001) sample (n similar to 2.0x10(16) cm(-3)) prepared by IBA also show an increased carrier concentration (similar to 10(18) 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 Angstrom into the material. The frequency of the surface plasmon is also strongly affected by surface normal, gives rise to the highest residual carrier concentrations, consistent with the generation of higher degrees of structural damage in the material.