Time-Resolved Study of Surface Recombination at Si(111) 2x1 Surfaces

Surface recombination of bulk photoexcited electrons at the cleaved Si(111) 2x1 surface has been studied using the technique of picosecond time- and angle-resolved photoemission spectroscopy. Population of the mid-gap pi sup * surface state could be directly observed in the photoemission spectrum as a result of the decay of photoexcited electrons from the bulk conduction band. The time dependence of the surface-state population was measured following excitation of a bulk electron-hole plasma by a 50 psec laser pulse at 532 nm. This could be directly compared to the surface-state decay dynamics measured following selective excitation of the pi sup * state by 2.8microns infrared laser pulses. In addition, photoemission of photoexcited carriers from the bulk conduction band provided a time-dependence of the bulk electrons in the vicinity of the surface.