Nowadays, epitaxial-growth techniques such as molecular-beam epitaxy (MBE) enable the layer-by-layer fabrication of semiconductor heterostructures with atomic precision . These techniques have made it possible to synthesize artificial crystal structures known as superlattices and quantum wells. One of our main projects at ICMAB is concerned with the MBE growth of low-dimensional heterostructures based on the type-IV semiconductors Si and Ge with addition of C. Recently, semiconductor technology has experienced a breakthrough while exploiting the self-organized growth of zero-dimensional (0D) structures, so-called quantum dots (QD), which display highly homogeneous size distributions and peculiar optical and electronic properties. Carrier confinement to lengths of the order of the de-Broglie wavelength leads to the formation of 0D-like density of states with sharp peaks at discrete energy levels and to an enhanced excitonic binding, both contributing to improve the performance of QD-based devices. In particular, we make use of predeposition of only 0.1 monolayer of carbon on Si to attain a higher density and narrower size distribution of Ge quantum dots.