Crystalline ripples at the surface of ion eroded strained Si_0.8Ge_0.2 epilayers

Surface erosion of a strained Si_0.8Ge_0.2 epilayer by 500 eV Ar⁺ ions with a fluence of 4 x10¹⁷ ions/cm² and the transformation from crystalline ripples to elongated Ge islands are reported by aligning the beam from 69° to 50° from the surface normal. Crystalline nature and the near surface Ge enrichment in such ripple structures are revealed by transmission electron microscopy. Moreover, ion beam induced decomposition of the SiGe network and the appearance of dislocation bands by suppressing the near-bandgap emission are manifested by u-Raman and photoluminescence studies, respectively.