Nanostructures on GaAs surfaces due to 60 keV Ar+-ion beam sputtering

The effect of 60 keV Ar+-ion beam sputtering on the surface topography of p-type GaAs(1 0 0) was investigated by varying angle of incidence of the ion (0–60°) with respect to substrate normal and the ion fluence (2 × 1017–3 × 1018 ions/cm2) at an ion flux of 3.75 × 1013 ions/cm2-s. For normal incidence and at a fluence of 2 × 1017 ions/cm2, holes and islands are observed with the former having an average size and density of 31 nm and 4.9 × 109 holes/cm2, respectively. For 30° and 45° off-normal incidence, in general, a smooth surface appears which is unaffected by increase of fluence. At 60° off-normal incidence dots are observed while for the highest fluence of 3 × 1018 ions/cm2 early stage of ripple formation along with dots is observed with amplitude of 4 nm. The applicability and limitations of the existing theories of ion induced pattern formation to account for the observed surface topographies are discussed.