Lifetime enhancement in the laser-induced periodic surface structures on Si (100) probed by ultrafast transient absorption spectroscopy

Laser-induced periodic surface structures are created by irradiating a Si(001) wafer with a femtosecond pulse laser, and then ultrafast transient absorption spectroscopy is carried out on these structures. The ultrafast charge carrier dynamics are reported on the sub-wavelength structuring obtained in a few microns up to hundreds of nm range, which are well below the diffraction limit and reveal the confinement effect. We observed a nearly three-fold increase in the lifetime of the generated hot carriers where several mechanisms and pathways alter the relaxation. The carrier recombination is observed to be slowed down as a result of the confinement due to structuring. This lifetime enhancement is investigated throughout a broad wavelength range of 400–1600 nm. By modulating the periodicity of the surface structures, which is implicitly dependent on the fluence and the number of laser pulses irradiation, it is possible to tune the relaxation lifetime of the material.