Zhang Wenjie, Guo Jiajia, Suo Peng, Lv Liping, Liu Junxing, Lin Xian, Jin Zuanming, Liu Weimin, Ma Guohong
Appl Opt. 2019 Oct 20;58(30):8200-8206. doi: 10.1364/AO.58.008200.
The speed of optical modulation on a terahertz (THz) pulse is mainly dominated by the optical response of the photocarrier. In order to achieve ultrafast THz modulation, the effective method is to reduce the lifetime of the photocarrier by introducing defects that can trap the photocarriers efficiently. In this paper, we reported the ultrafast optical modulation of THz switching in a 10 nm CdTe nanostructure film. After photoexcitation at 800/400 nm, the THz response of the film is extremely fast with a lifetime of ${\sim}{1.3};{\rm ps}$∼1.3ps. Further, the ultrafast transient THz transmission shows almost temperature independence down to 100 K. On the other hand, the transient absorption spectroscopy reveals that the lifetime of photocarriers in CdTe nanostructure film lasts as long as several ns. The 1.3 ps THz photoconductivity response is due to the substantial decrease of photocarrier mobility in a CdTe nanostructure, which comes from the increase of the photocarrier scattering between the photocarrier and the surface states of CdTe nanostructural film. Our experimental results provide a new method to design optically driven ultrafast THz response devices, such as THz switch and THz modulator.
太赫兹（THz）脉冲的光学调制速度主要由光载流子的光学响应决定。为了实现超快太赫兹调制，有效的方法是通过引入能够有效俘获光载流子的缺陷来降低光载流子的寿命。在本文中，我们报道了在10 nm碲化镉（CdTe）纳米结构薄膜中太赫兹开关的超快光学调制。在800/400 nm光激发后，该薄膜的太赫兹响应极快，寿命约为1.3 ps。此外，超快瞬态太赫兹透射率在低至100 K时几乎与温度无关。另一方面，瞬态吸收光谱表明，碲化镉纳米结构薄膜中的光载流子寿命长达数纳秒。1.3 ps的太赫兹光电导响应是由于碲化镉纳米结构中光载流子迁移率的大幅降低，这源于光载流子与碲化镉纳米结构薄膜表面态之间光载流子散射的增加。我们的实验结果为设计光驱动超快太赫兹响应器件，如太赫兹开关和太赫兹调制器，提供了一种新方法。
