Lifetime of an electron-hole plasma of silicon in the picosecond range

The temporal and spatial evolution of the e-h plasma in Si, during and after excitation with intense picosecond laser pulses, is central to understanding the pulsed-laser annealing mechanism and, in particular, to the energy transfer from the e-h plasma to the lattice. Reflectivity and transmission measurements in the ps and fs range, which contain the signature of the e-h plasma, have aroused intense interest in several recent studies. Here the authors present such measurements in the ps range, which clearly show loss of the e-h plasmon signature, at roughly 15 ps after the pump laser pulse, for densities (equivalently plasma frequencies omega/sub p/) comparable to or greater than the indirect gap energy E/sub i/(T). The authors attribute this plasmon loss to a new recombination channel with a lifetime tau similarly ordered 100 fs