Evolution of nanostructures during low-energy ion-sputtering

The morphological evolution of nanostructures on semiconductor surfaces eroded by low-energy ion beams has gained particular interest recently as a possible way to generate regular, ordered, and highly dense quantum dots. Generally, the erosion by ion beams increases the surface roughness, which under certain sputter conditions can turn to periodic surface structures. At normal incidence of the ion beam hexagonally arranged dot patterns appear on the eroded surface. The diameter of these structures is in the range of 15 - 80 nm depending on ion energy with a density up to 2x10^11cm^-2.
After an initial stage of irradiation the temporal evolution of the dot pattern can be described by a stochastic continuum equation. In the case of crystalline semiconductor surfaces rapid amorphization and variation in stoichiometry takes place. As the erosion process proceeds nanoscale dot structures appear at the surface, which are remarkable well ordered and grow up to an aspect ratio of nearly unity. We present the temporal evolution of dot pattern formation on GaSb (100) surfaces during Ar+ ion sputtering. The characteristic length of the dot pattern is determined as a function of ion energy, ion current density, and sample temperature.