Design rules to control the tensile strain in Ge μ-membranes fabricated from GeOI substrates for photonics applications

Applying the right tensile strain to suspended membranes [1] can make Germanium a direct band-gap semiconductor, which is most promising way to low-threshold lasing [2]. The current key to reach the targeted high tensile strain is the quality of the Germanium. Epitaxied Germanium (Ge) on Silicon (Si) suffers from dislocations at its interface due to the lattice mismatch between Si and Ge (Figure 1 a). Higher crystalline quality can be obtained by fabricating Germanium on Insulator (GeOI) substrates by Smart Cut™ technology [3]. However, the processing has to be adapted to obtain specific “optical” GeOI substrates [4], much thicker than standard microelectronics GeOI.