基于光抽运-太赫兹探测技术的ZnSe纳米薄膜的光致载流子动力学特性

Photocarriers dynamics in zinc selenide nanocrystal studied with optical pump-Terahertz probe spectroscopy

利用光抽运-太赫兹探测技术,研究了ZnSe纳米薄膜的载流子弛豫过程和太赫兹波段电导率的时间演化过程。通过监测THz探测脉冲的变化,系统地研究了ZnSe纳米晶在光激发载流子诱导下的瞬态光电导特性,并用Drude-Smith模型对瞬态电导率进行了拟合。在400 nm的激光脉冲激励下,太赫兹脉冲的负透过率呈现出超快的上升和双指数衰减现象。时间常数为5 ps的快速衰减过程主要由ZnSe纳米晶界面缺陷处的光载流子后向散射控制,而时间常数大于1 ns的慢衰减过程主要是由载流子从导带到价带的复合引起的。瞬态电导率随时间的演化表明,ZnSe纳米材料是制备超快THz开关的很好的备选材料。

The carrier relaxation process and the time evolution process of the conductivity in the terahertz band of the ZnSe nanocrystal are investigated by optical-pump terahertz-probe spectroscopy at room temperature.Monitoring the changes of the THz probe pulse,the transient photoconductive properties of ZnSe nanocrystals induced by photoexcited carriers were systematically studied,and the transient conductivity was fitted with the Drude-Smith model.With the laser pulse excitation at 400 nm and the pump power is 10 mW and 16 mW,the negative transmission of terahertz pulse shows an ultrafast rising process followed by a recovery process.The recovery process obviously consists of two parts:fast and slow,and can be well fitted with a biexponential decay curve.The fast decay component with time constant of 5 ps is mainly controlled by the backscattering of photocarriers at the interface defects of ZnSe nanocrystal,and the slow decay component with time constant greater than 1 ns is mainly caused by the recombination of carriers from the conduction band to the valence band.The evolution of conductivity with time demonstrates that this kind of nanostructure is a good candidate for fabricating ultrafast terahertz switching.