Investigation of the impact of surface state on Ge membrane quality obtained with porous lift-off

Germanium (Ge) substrates are widely used for the integration of III–V-based devices owing to their suitable material properties. However, their high cost, driven by material scarcity and complex processing requirements, remains a major limitation for large-scale production. In this work, the growth of III–V materials on Ge nanomembranes (Ge NMs) fabricated from unpolished Ge substrates was investigated. The results demonstrate a promising approach for replacing costly epi-ready, polished Ge wafers with unpolished Ge wafers, potentially enabling a more cost-effective substrate platform for III–V device integration. Using a porous lift-off approach on the 4-in. unpolished wafers, homogeneous porous Ge layers were achieved. These layers enabled the formation of monocrystalline Ge NMs with root mean square roughness values ranging from 0.7 to 1.4 nm at the nanoscale and preserved crystallographic orientation and allowed subsequent detachment. Furthermore, the nano-membranes supported high-quality III–V epitaxial growth, demonstrating a promising pathway toward lower-cost scalable production of III–V on Ge devices.