Picosecond pulsed laser ablation of silicon: a molecular-dynamics study

We report here the continuation of our earlier work on the molecular-dynamics simulations of laser ablation of silicon with picosecond laser pulses. A more realistic phenomenon of ablation is observed as, along with a signi®cant expansion of the time scale, carrier diffusion is explicitly taken into account. The motion of approximately 32,000 atoms, contained in a 5nm 5 nm 27 nm surface rectangular box irradiated by a single 308 nm, 10 ps, Gaussian laser pulse, is followed for typically 100 ps of simulation time. Because melting and possibly ablation or desorption of the target following absorption of the laser pulse are described within the thermal annealing model, care is taken not to exceed carrier densities of 1022 cmÿ3. More precisely, the interaction of photons with the target is thought to cause the generation of a dense gas of hot electrons and holes which primarily relaxes through carrier-phonon scattering. Above a characteristic threshold energy of 0.30 J/cm2, ejection from the target of big chunks of molten material occurs and the latter are expelled with axial velocities of 1000 m/s. # 2000 Elsevier Science B.V. All rights reserved