Measurement of ultrafast hot-carrier relaxation in silicon by thin-film-enhanced, time-resolved reflectivity

Time-resolved reflectivity measurements with ∼100 fs resolution have revealed an initial 350 fs relaxation time in silicon, believed to be the time it takes hot, photoinjected carriers to relax to the band edge. The measurements were made at low carrier densities (∼1017 cm-3) for which carrier-carrier processes are negligible, and were facilitated by the greater than order of magnitude enhancement of the change in reflectivity signals that can be produced by the use of thin films.