Growth process of GaAs ripples as a function of incident Ar-ion dose

We report periodic ripple formation on GaAs sputtered by 60 keV Ar ions at an angle of 60° over a large range of ion doses from 1 × 1017 to 1 × 1019 ions/cm2 under Atomic Force Microscopy (AFM) study. Initially in the dose range between 1 × 1017 and 4 × 1017 ions/cm2, only very small roughness is formed on the surface and from the dose of 5 × 1017 ions/cm2, the ripples start to form and attain a well-defined structure at a dose around 9 × 1017 ions/cm2, remain stable and then from a dose of 4 × 1018 ions/cm2, the ripple structures become very rough, periodicity breaks down and step-like features become prominent all over the surface. Parameters like rms roughness, ripple wavelength, amplitude etc. are measured from the AFM image analysis. The results are discussed with the help existing formalism with the understanding of preferential sputtering of one of the components of GaAs.