Dynamics and second-order nonlinear optical susceptibility of photoexcited carriers at Si(111) interfaces

An interface specific investigation, by time-resolved second-harmonic generation, shows that photoexcited carrier dynamics at Si(111) interfaces depend strongly on surface termination. Oxide- and H-terminated surfaces show distinct transient behavior, with a surface recombination velocity $<103 cm/s.$ Incompletely H-terminated Si(111) shows faster dynamics, correlating with less interface passivation. A simple model reveals that the second-order nonlinear optical susceptibility of photoexcited carriers is two orders of magnitude greater than that of the valence band electrons.