Surface morphology and structural modifications of Si targets submitted to intense pulsed-laser irradiations

Crystalline silicon samples (with or without their native oxide layer) have been submitted to intense optical irradiations generated by laser sources delivering pulses of different durations (in the ns or μs regimes) in the visible (≈ 550 nm) or in the near infrared (≈ 1000 nm). The different stages of the morphological surface alterations and the possible inherent structural modifications were studied as a function of the incident energy fluence using optical or electronic microscopies and Raman scattering. For both types of samples, special attention was paid to the determination of the threshold fluence for surface melting and these results were compared with predictions obtained by solving the one-dimensional time-dependent heat-flow equation. Raman investigations have revealed that excepted for specific locations in the crater boundary, the irradiated area presents a good crystalline quality. Des echantillons monocristallins de Si (avec ou sans leur couche d'oxyde natif) ont ete irradies a l'aide de sources laser intenses emettant des pulses (regime de la nano ou de la microseconde) dans le visible (≈550 nm) ou dans le proche infrarouge (≈1000 nm). En fonction de la fluence energetique incidente, la succession des alterations de surface ainsi que les possibles changements structurels ont ete etudies par microscopie optique ou electronique ainsi que par diffusion Raman. En particulier, la fluence critique correspondant a la fusion de surface a ete determinee pour chaque type d'echantillon. Les donnees experimentales ont ete comparees aux resultats obtenus en resolvant l'equation monodimensionelle de la propagation de la chaleur dependante du temps. Les etudes Raman ont montre que les zones irradiees, a l'exception de microdomaines generalement situes en bordure des crateres d'impact, presentent un excellent etat cristallin.