Ion energy dependence of nanodot formation by nitrogen-bombarded InP

When InP is bombarded with noble gas ions or nitrogen ions, nano-scaled sputter cones appear on the surface. In this study, we report on the ion energy dependence of the surface topography due to nitrogen ion bombardment. InP(1 0 0) substrates were bombarded with 1–5 keV N2+ ions at an angle of incidence of 41° with respect to the normal. The fluence was fixed at 5×1016N2+cm-2. The topographies of the virgin and bombarded samples were investigated by AFM (atomic force microscopy) and high-resolution SEM (scanning electron microscopy). There are similarities between the topographies of the nitrogen-bombarded surfaces to those reported for noble gas ion bombardment. The AFM-measured topographies were quantified in terms of the root mean square (rms) roughness. The rms of 12 roughness initially decreases from a high value at 0.5 keV per nitrogen atom to reach a minimum somewhere between 1.5 and 2 keV per nitrogen atom. The results are compared to the results reported for noble gas ion-bombarded InP and to the standard theories in this field. In general, the rms roughness as a function of ion energy is ion mass dependent, in agreement with results reported for ripples on Si and GaAs. However, there seems to be only a slight dependence on the chemical reactivity of the bombarding ions with the InP substrate. No ripples were observed on the samples.