Periodic surface structure bifurcation induced by ultrafast laser generated point defect diffusion in GaAs

摘要

The formation of high spatial frequency laser induced periodic surface structures (HSFL) with period ＜0.3 λ in GaAs after irradiation with femtosecond laser pulses in air is studied. We have identified a point defect generation mechanism that operates in a specific range of fluences in semiconductors between the band-gap closure and ultrafast-melt thresholds that produces vacancy/ interstitial pairs. Stress relaxation, via diffusing defects, forms the 350-400 nm tall and ～90nm wide structures through a bifurcation process of lower spatial frequency surface structures. The resulting HSFL are predominately epitaxial single crystals and retain the original GaAs stoichiome-try.