Counterbalanced Effect of Surface Trap and Auger Recombination on the Transverse Terahertz Carrier Dynamics in Silicon Nanowires

The surface-trap mediated carrier recombination is a crucial feature in characterizing the optoelectronic properties of nanowires (NWs). Due to the one-dimensional characteristics, the photoexcited carriers experiences multiple carrier interactions in the transverse direction such that strong carrier-carrier interactions are expected to play an important role in the NW carrier recombination. Here, using ultrafast optical-pump and terahertz-probe spectroscopy, we show that the Auger scattering significantly reduces the trap-mediated decay process. Systematic studies on bulk Si, bundled, individual, and encapsulated (reduced surface-trap density) SiNWs reveal that the effect of Auger recombination exhibits strong pump-fluence dependence depending on the surface-treatment condition.