In this contribution, we report on the growth of Ge inside extremely thin 16-nm thick cavities through selective lateral growth of Ge on 300 mm silicon-on-insulator (0 0 1) substrates. We showed that the density of defects depends on the cavity shape, with extended defects such as micro-twins and stacking faults observed on the top surface along the < 110 > directions when the Si/Ge growth interface is along the < 110 > directions. The optimization of the cavity shape, by tuning the etching conditions, leads to a significant reduction of the defects in the Ge nanostructures, and this approach paves the road towards the co-integration of Si and Ge based devices. (C) 2018 Elsevier B.V. All rights reserved.