In this work, we discuss the characteristics of particular island-type features with an amorphous core that are developed during the low temperature epitaxial growth of Ge and GeSn layers by means of chemical vapor deposition with Ge2H6. Although further investigations are needed to unambiguously identify the origin of these features, we suggest that they are originated by the formation of clusters of H and/or contaminants atoms during growth. These would initially cause the formation of pits with crystalline rough facets over them, resulting in ring-shaped islands. Then, when an excess surface energy is overcome, an amorphous phase would nucleate inside the pits and fill them. Reducing the pressure and/or increasing the growth temperature can be effective ways to prevent the formation of these features, likely due to a reduction of the surface passivation from H and/or contaminant atoms. (C) 2015 Elsevier B.V. All rights reserved.