DLIP met LIPSS: Hybrid dual periodic laser patterning of semiconductors

The fabrication of micro- and nanometric structures in semiconductors with ultrashort laser pulses offers enormous potential due to their tunable morphological, electronic and optical properties. Two well-established methods for this purpose are patterning based on Laser Induced Periodic Surface Structures (LIPSS) and Direct Laser Interference Patterning (DLIP). As both techniques rely on different physical phenomena, a combination of both approaches is feasible, allowing a wide range of combinations for high-precision laser patterning by superimposing LIPSS in a DLIP pattern. Here, we report the fabrication of hybrid nanostructures in silicon and germanium by multipulse femtosecond laser irradiation (λ = 800 nm, τ = 120 fs) in a versatile DLIP configuration. This configuration allows the control of the fringe modulation depth (100 % - 0 %), the DLIP pattern type (fringes or dots) and their period (5 µm – 1.25 µm). For fringe patterning, linear laser polarization either parallel or perpendicular to the DLIP fringes is used, leading to single or dual LIPSS with different periods along both plane directions depending on the irradiation conditions. These results show that this strategy allows to achieve highly tunable LIPSS periods, far beyond the conventional scaling of λ, λ/2 and λ/4. The results reported here explore a promising new pathway for the fabrication of functional surfaces with controllable periods in 2D for a wide range of potential applications in relevant fields as photonics and coating technologies.