Cd_(0.96)Zn_(0.04)Te光致载流子动力学特性的太赫兹光谱研究

Photocarrier dynamics in Cd_(0.96)Zn_(0.04)Te measured by optical-pump terahertz-probe spectroscopy

采用光抽运-太赫兹探测技术研究Cd_(0.96)Zn_(0.04)Te的载流子弛豫和瞬:态电导率特性.在中心波长800 nm的飞秒抽运光激发下,Cd_(0.96)Zn_(0.04)Te的载流子弛豫过程用单指数函数进行了拟合,其载流子弛豫时间长达几个纳秒,且在一定光激发载流子浓度范围内随光激发载流子浓度的增大而减小,这与电子-空穴对的辐射复合有关.在低.光激发载流子浓度(4.51×10^(16)—1.81×10^(17)cm^(-3))下,Cd_(0.96)Zn_(0.04)Te的太赫兹(terahertz,THz)瞬态透射变化率不随光激发载流子浓度增大而变化,主要是由于陷阱填充效应造成的载流子损失与光激发新增的载流子数量近似.随着光激发载流子浓度继续增大(1.81×10^(17)—1.44×10^(18)cm^(-3)),THz瞬态透射变化率随光激发载流子浓度的增大而线性增大,是由于缺陷逐渐被填满,陷阱填充效应造成的载流子损失与光激发新增的载流子数量相比可忽略不计.在光激发载流子浓度为1.44×10^(18)—2.17×10^(18)cm^(-3)时,Cd_(0.96)Zn_(0.04)Te对800 nm抽运光的吸收达到饱和,THz瞬态透射变化率不再随光激发载流子浓度增大而变化.不同光激发载流子浓度下Cd_(0.96)Zn_(0.04)Te在THz波段的瞬态电导率用Drude-Smith模型进行了很好的拟合.此研究为碲锌镉探测器的设计和制备提供重要数据支撑和理论依据.

Photogenerated carrier relaxation process and terahertz conductivity of Cd_(0.96)Zn_(0.04)Te are investigated by optical pump-terahertz probe spectroscopy at room temperature.With photoexcitation at 800 nm,the photogenerated carrier recovery process can be fitted with a single exponential curve,and its recovery time lasts several nanoseconds,which decreases with the increase of photo generated carrier densities in a certain range of photogenerated carrier densities,relating to the radiative recombination of electron-hole pairs.The transient transmittance change of terahertz pulse remains the same with the photogenerated carrier densities increasing from 4.51×10^(16)cm^(-3)to 1.81×10^(17)cm^(-3),which is because the number of loss carriers by defect trapping is approximate to the augment of carriers by photoexcitation.As the photo generated carrier density increases from 1.81×10^(17)cm^(-3)to 1.44×10^(18)cm^(-3),the magnitude of photoinduced absorption increases linearly with the increase of photo generated carrier density due to the fact that most of the defects are occupied.When the photogenerated carrier densities are higher than 1.44×10^(18)cm^(-3),the magnitude of photoinduced absorption remains almost thhe same,because the absorption of 800 nm pump pulse reaches a saturation level.The evolution of complex conductivity with photogenerated carrier density in a delay time of about 50 ps can be well fitted with Drude-Smith model.Our analysis provides an important data support and theoretical basis for designing and fabricating of Cd1-xZnxTe detection.