飞秒激光作用下单晶硅表面载流子的超快动力学研究

摘要

The reflectivity change of crystalline silicon is studied using femtosecond pump-probe technique with different pump pulse energies,and the ultrafast dynamics process of the sample is analyzed.The laser pulse width used in the experiment is 120 fs,and the wavelengths of the pump and probe are 400 and 800 nm respectively.The research results demonstrate that the reflectivity changing of crystalline silicon will reach a peak value rapidly,after which a fast decay and a slow decay processes will follow up.The fast decay process is mainly induced by carrier-carrier scattering and carrier-phonon scattering,while the slow decay process is induced by carrier recombination and carrier diffusion.By fitting the experiment data with the bi-exponential model,the coefficient C of the bi-exponential model and the fast decay constant τf are obtained.Data comparison demonstrates that the time of the fast decay process becomes longer and the proportion of fast decay process enlarges with the pump energy increasing.%利用飞秒激光泵浦-探测技术研究单晶硅在不同脉冲能量作用下的瞬态反射率变化,进而分析单晶硅表面载流子的超快动力学过程.实验所用飞秒激光脉冲宽度为120 fs,泵浦光和探测光波长分别为400和800 nm.研究结果表明:飞秒激光作用后,单晶硅表面反射率变化迅速达到峰值,然后经历一个快弛豫过程和一个慢弛豫过程.快弛豫过程包括载流子-载流子散射和载流子-光学声子散射,慢弛豫过程包括载流子复合过程和扩散过程.利用双e指数模型对实验结果进行拟合,求出双e指数系数C及快弛豫时间τf.通过实验数据对比分析发现,泵浦光脉冲能量越大,快弛豫时间越长,所占的比例越大.