Wafer-scale porous germanium bilayer structure formation by fast bipolar electrochemical etching

Abstract

Recently, porous Germanium (PGe) structures have gained significant attention as a promising engineering material for a broad range of applications due to the versatility of its intrinsic physical and chemical properties. The Conventional Bipolar Electrochemical Etching (CBEE) technique favours a cost-effective and controlled synthesis of PGe layers, to tune the structural properties. However, some challenges still persist. Specifically, the etch rate of these layers remains low limited, resulting in extended process times. Achieving low porosity layers (< 40 %) remains unclear, and addressing the development of a non-sponge morphology is necessary for various fields, such as batteries. In this work, we investigate the impact of the anodic current density and electrolyte ratio on tubular single PGe layer (T-PGe) morphology with low porosities using a Fast Bipolar Electrochemical Etching (FBEE) process. We have demonstrated T-PGe structures with no parasitic sponge-like layer on top, providing insights to control their occurrence. We establish the feasibility of such layers as a template for the formation of tubular bilayers on the wafer's scale. This approach emphasizes the fast synthesis of promising T-PGe structures with low porosities (< 40 %).