Enhancing anti-reflection properties of laser nanotextured Indium Phosphide

In this study, we investigated the enhancement of anti-reflection properties of p-type Indium Phosphide through the formation of regular and homogeneous Laser-Induced Periodic Surface Structures (LIPSS). We utilized a laser system that generated pulses with a duration of 100 fs, a wavelength of 800 nm, and a repetition rate of 1 kHz. LIPSS fabrication over large areas (12 × 12 mm²) led to a significant reduction in reflectance, ranging from approximately 35 % to 50 % within the 300 – 930 nm wavelength range, compared to pristine p-type InP. By systematically varying laser fluence and beam scanning overlaps, we identified optimal conditions for highly regular LIPSS formation at a single pulse fluence of approximately 43 mJ cm⁻² and a scanning speed of 4 mm/s. The regularity of LIPSS was evaluated using a two-dimensional Fourier transform to study the dispersion of spatial frequencies and orientation angles. Our findings show a clear correlation between enhanced anti-reflection properties and LIPSS regularity. Specifically, surfaces with more homogeneous LIPSS, as indicated by lower dispersion of LIPSS orientation angles, exhibited lower reflectance. We further explored the effects of laser pulse energy on surface properties by using Raman spectroscopy. Results indicated a decrease in first-order modes intensity and asymmetric broadening of the Transverse Optical mode when the laser energy increased, suggesting surface modifications and lattice disorder. The analysis also pointed to the introduction of tensile stress within the lattice. However, the detection of second-order modes across all laser-treated samples indicated that long-range crystallinity was retained. These findings offer valuable insights into optimizing surface properties for various optoelectronic and photonic applications where minimizing reflection is crucial for device performance and efficiency.