Time-resolved photoluminescence of silicon microstructures fabricated by femtosecond laser in air

Spatial distribution characteristics of plumes induced by femtosecond laser ablation of silicon in vacuum

The spatial distribution characteristics of plumes induced by femtosecond laser ablation of silicon in vacuum are studied by using spectroscopy. The plume spatial distribution clearly shows two zones with different characteristics. The center of the first zone is at a distance of approximately 0.5 mm from the target. Silicon ionic radiation, recombination radiation, and bremsstrahlung mainly occur in this zone, causing an exponential decay with a decay constant of approximately 0.151-0.163 mm. The second zone with a greater area, whose center is at a distance of approximately 1.5 mm from the target, follows the first zone. In this zone, the radiation from silicon atoms and electron-atom collisions dominates, leading to an allometric decay with an allometric exponent of approximately - 1.475 to - 1.376. In the second zone, the electron density spatial distribution is approximately arrowhead-shaped, which is potentially induced by collisions between ambient molecules and the particles in front of the plume. These results indicate that both the recombination effect and expansion effect play important roles and compete with each other in plumes. The recombination effect is dominant near the silicon surface, causing exponential decay. As the distance increases, the electron density decreases exponentially by recombination, causing a more intense expansion effect.

Electronic states of defect with impurity and infrared emission on black silicon prepared by an ns-laser

It is found that the optimum annealing temperature is about 1000°C for the infrared emission of defect states at room temperature on black silicon (BS) prepared by using a nanosecond-pulsed laser. In addition, it is observed that the suitable annealing time is 6∼8  min at 1000°C for the emission on the BS. The crystallizing proceeding in annealing on the BS can be used to explain the above annealing effect. It is interesting that the emission band becomes intensive and broader on the BS prepared in oxygen atmosphere than that prepared in vacuum in the analysis of photoluminescence spectra, where the electronic states localized at the defects from D1 to D4 doped with oxygen play an important role in the emission with the broader band which are obviously enhanced in the room temperature.