Comprehensive investigation of thermal induced reorganization of porous-germanium structures

Porous germanium (PGe) substrates have recently attracted significant attention for the development of lightweight and flexible solar cells and optoelectronic devices. A reliable approach for releasing epitaxial layers based on Germanium and reusing the substrate involves utilizing a bilayer structure of PGe. The growth of such detachable devices holds great potential for integration onto the Si platform. The used structure of PGe is made of a low-porosity layer serving as epitaxial seed on top of high-porosity one used as a weak separation layer. In this work, we investigate the impact of thermal annealing on the PGe morphology for deeper understanding of the mechanisms involved in the formation of the epitaxial seed layer and the voided weak layer underneath. Indeed, thermal-induced reconstruction has been investigated at various annealing temperatures and times for PGe layers with differing porosity levels, encompassing low, high, and gradual porosity profiles. Our findings reveal the formation of a modified substrate at low annealing temperatures, resulting in a suspended membrane on top of the fragile separation layer, rendering it suitable for detachment and subsequent substrate reuse.