Sub-micron periodic structuring of sapphire by laser induced backside wet etching technique

The periodic structuring of sapphire, by using laser induced backside wet etching technique (LIBWE) and 266 nm, 150 ps Nd:YAG laser radiation, is demonstrated here for first time. Sub-micron period Bragg reflectors are successfully patterned in sapphire wafers using modest energy densities and number of pulses. The gratings are characterized using diffraction efficiency measurements, AFM, and SEM. Issues related to the ablation process and to the phase mask holography are presented and discussed. The experimental results presented depict that the applied method is capable to produce relief structures of depth as deep as 100 nm, while maintaining high resolutions, close to the thermal diffusion length of the material corresponding to the ultrashort pulse duration.