Evolution of terahertz conductivity in ZnSe nanocrystal investigated with optical-pump terahertz-probe spectroscopy

Ultrafast carrier dynamics and terahertz conductivity of ZnSe nanocrystal are investigated by means of the optical-pump terahertz-probe spectroscopy at room temperature. With the laser pulse excitation at 400 nm, the negative transmission of terahertz pulse shows an ultrafast rising followed by a biexponential recovery. The fast decay component with time constant of 5 ps is dominated by the photocarriers backscattering at interfaces of ZnSe nanoparticles, and the slow one with time constant longer than 1 ns can be assigned to the carrier recombination from band-to-band transition. The evolution of conductivity with time demonstrates that this kind of nanostructure is a good candidate for fabricating ultrafast terahertz switching.