Ultrafast nonlinear response of high density carriers at silicon surface detected by simultaneous measurements of transient reflecting first and second order diffractions

摘要

The simultaneous detections of transient reflectivity (TR), transient reflecting first and second order diffraction signals, at a silicon surface revealed that each signal reflected different physical processes of carrier dynamics under a high pump power of 5 mJ/cm~(2). It was shown that the second order diffraction could detect a refractive index change which was not linearly dependent on the excited carrier density, and it was suggested that the nonlinearity was caused by many-body interactions among carriers at the band-edge states. The dynamics observed with the second order diffraction corresponded to the recombination of the band-edge carriers. Analysis of the first and second order diffractions in combination with the recently developed spectroscopic detection provided selective information on the ultrafast carrier and heat dynamics for a silicon surface, that is, carrier-phonon scattering, recombination of carriers, heat generation, and diffusion. Additionally, it was shown the TR might allow observation of mixed physical processes detected by the first and second order diffractions and it was suggested that deducing exact physical processes only from the TR signal, especially under high pump power conditions, was difficult.