Wide-spectral absorption of femtosecond laser textured germanium

This work focuses on addressing limitations in the optical properties of germanium (Ge), especially concerning reflections from the planar surface and for sub-bandgap wavelengths (>1.7 µm). To overcome these challenges, femtosecond laser processing is employed. The study explores the impact of fs-laser texturing on crystalline Ge wafers, highlighting the potential benefits of induced surface micro- and nanostructures in improving optical absorption. The experiment involves varying laser power and scan speed, and the results show a significant enhancement in absorptance in a wide spectral range of 0.25 – 2.5 µm. The obtained high absorptance outperforms fs-laser textured silicon at wavelengths exceeding 1 µm, suggesting promising applications for fs-laser-textured Ge in infrared optical and optoelectronic technologies.