Environment-Friendly Non-noble Metal-Assisted Anodic Etching of Ge without Acids and Oxidants

Metal-assisted chemical etching (MACE) is a wet-based anisotropic etching technology designed to address the high cost and surface damage of dry etching. While extensively explored for Si and GaAs, its application to Ge has been underexplored, particularly in achieving cleanly etched surfaces. In this study, we introduced metal-assisted anodic etching (MAAE) as an alternative to minimize Ge surface damage. By leveraging MAAE’s distinctive properties, including electric current and germanium oxide characteristics, we achieved Ge etching without reliance on acids or oxidants, showcasing a cleaner, more efficient method. Atomic force microscopy (AFM) analysis demonstrated that MAAE significantly reduced surface roughness, achieving an RMS value of 2.478 nm─substantially lower than the over 10 nm observed with conventional MACE. Additionally, we explored non-noble metals, rarely employed in MACE, for Ge microstructure fabrication. This novel process eliminates reliance on acids, oxidants, and noble metals. By avoiding these materials, the proposed method not only minimizes chemical waste, offering an environmentally sustainable solution, but also significantly reduces fabrication costs. This study highlights a practical, sustainable, and cost-effective alternative to both reactive ion etching and conventional MACE for fabricating high-quality Ge nano- and microstructures.