Density behaviors of Ge nanodots self-assembled by ion beam sputtering deposition

Self-assembled Ge nanodots with areal number density up to 2.33×10¹⁰ cm^-2 and aspect ratio larger than 0.12 are prepared by ion beam sputtering deposition. The dot density, a function of deposition rate and Ge coverage, is observed to be limited mainly by the transformation from two-dimensional precursors to three-dimensional islands, and to be associated with the adatom behaviors of attachment and detachment from the islands. An unusual increasing temperature dependence of nanodot density is also revealed when high ion energy is employed in sputtering deposition, and is shown to be related with the breaking down of the superstrained wetting layer. This result is attributed to the interaction between energetic atoms and the growth surface, which mediates island nucleation.