Research on Friction-induced Selective Etching for Low Reflectance Germanium Surface

The single-crystal germanium superstructure surface exhibits remarkable characteristics of low reflectance, while maintaining high infrared refractive index, low absorption, low dispersion, and high-temperature resistance, providing an ideal choice for the development of high-performance infrared optical devices, infrared thermal radiation control, optical coatings, and anti-reflection technologies. Wet selective etching exhibits characteristics such as high efficiency and good uniformity in fabricating specific surface structures, providing advantages in nanofabrication on the surface of various anisotropic materials. However, the anisotropic wet etching characteristics on the surface of single crystal germanium are not significant, which has resulted in slow progress in wet etching processes. Consequently, it is still challenging to achieve the controllable fabrication of nanostructures on single crystal germanium using wet etching methods. Additionally, the processing technology for achieving ultra-low reflectance surfaces on single crystal germanium faces technical challenges such as susceptibility to damage, low efficiency, complex processes, and high costs. To address this issue, a friction-induced selective etching method based on H2O2-NaOH etchants has achieved controllable anisotropic etching on the surface of single crystal germanium, overcoming the bottleneck issue of conventional wet etching techniques in direct fabrication of nanostructures on single crystal germanium surfaces. Finally, multiple single crystal germanium super structured surfaces were fabricated using this method, achieving an ultra-low reflectance of 13% within the wavelength range of 800-1 800 nm. This unique nanofabrication technique provides a new solution for the controlled construction of low-reflectance single crystal germanium superstructures on surfaces. © 2024 Chinese Mechanical Engineering Society. All rights reserved.