Computer Model of the Temperature and Carrier Concentration Induced in Si by Nanosecond and Picosecond Laser Pulses

ABSTRACTA set of simultaneous equations for lattice temperature, carrier concentration and carrier temperature in Si is numerically solved for typical nanosecond and picosecond laser pulses. The calculated threshold energies required to reach Si melting temperature are consistent with measured thresholds to reach a flat-top reflectivity of ~ 70% for typical nanosecond pulses at 1.06 and .53 µm. In the picosecond regime, almost the entire pulse energy is at first stored in the carrier system, and a carrier temperature exceeding 30,000 K is achieved for a 3 J/cm2, 30 ps pulse at 1.06 µm. In this case, the surface carrier concentration reaches a high enough value to cause an enhanced reflectivity from the plasma lasting for at least 0.1 ns. The lattice temperature reaches 1410°C, while carriers relax their energy to the lattice after the pulse, and the energy stored in the carrier system would be enough to supply the heat of fusion at the silicon surface.