Pump fluence dependence of ultrafast carrier dynamics in bulk ZnSe

Ultrafast carrier dynamics of bulk ZnSe is investigated by means of the optical-pump terahertz-probe spectroscopy with pump fluence ranging from 38 to 239 μJ/cm 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 relaxation time of fast decay and slow one is increased with pump fluence. This trend is expected for surface states filling, which may inhibit carrier lifetime. Keywords—bulk ZnSe; optical-pump terahertz-probe spectroscopy; carrier dynamics