We present a novel self-assembly route to align SiGe quantum dots. By a combination of theoretical analyses and experimental investigation, we show that epitaxial SiGe quantum dots can cluster in ordered closely packed assemblies, revealing an attractive phenomenon. We compute nucleation energy barriers, accounting for elastic effects between quantum dots through both elastic energy and strain-dependent surface energy. If the former is mostly repulsive, we show that the decrease in the surface energy close to an existing island reduces the nucleation barrier. It subsequently increases the probability of nucleation close to an existing island, and turns out to be equivalent to an effective attraction between dots. We show by Monte-Carlo simulations that this effect describes well the experimental results, revealing a new mechanism ruling self-organisation of quantum dots. Such a generic process could be observed in various heterogeneous systems and could pave the way for a wide range of applications.