Sequential fabrication of multiple Ge nanomembranes from a single wafer: Towards sustainable recycling of Ge substrates

Abstract

Germanium (Ge) substrates are employed for III-V multijunction solar cells (MJSCs). However, due to limited availability and environmental impact, Ge is a critical raw material. Detachable Ge nanomembranes (NMs) are gaining attention to reduce Ge consumption through substrate reuse. The Porous germanium Efficient Epitaxial LayEr Release (PEELER) process enables Ge NM detachment and substrate reuse, reducing costs and Ge material consumption. In this work, we demonstrate the sequential production of three NMs from one parent substrate using the PEELER process, yielding monocrystalline NMs, with a surface suitable for further epitaxial growth of III-V layers (RMS < 3.2 nm). By avoiding the costly Chemical Mechanical Polishing (CMP), our approach enables a more economical and sustainable production of high-efficiency Ge-based solar cells, compared to the conventional production process.