化合物半导体中自旋相关多体效应的理论研究

The electrons will occupy the states at the bottom of the conduction band if semiconductor is excited by femtosecond circularly polarized laser pulse. The electron spins align according to optical orientation and result in the changes in absorption, transmissivity and reflectivity. In this project we study theoretically the influence of electron spin on pump probe spectroscopy in semiconductors with slightly above the band gap energy and high carrier density. In this model all spin-dependent effects, such as, the band filling effect, band gap renormalization, free carrier absorption are explicitly included. We will manage to explore the transmissivity and reflectivity as a function of carrier density and photon energy and compare the calculational data to the relative experiments. The expected results obtained in this project will not only be the basis of the ultrafast pump probe transmission/reflectivity spectra, but also will interpret the observed complex experimental phenomena.

半导体受到圆偏振超短激光脉冲激发时，价带电子发生跃迁，根据光学取向原理，在导带形成电子自旋布局，使得吸收系数、透射率和反射率均发生变化。本项目拟探索半导体中近带隙、高载流子浓度下，电子自旋对抽运探测透射/反射光谱的影响。考虑带填充效应、多体效应和自由载流子吸收等效应，建立透射/反射率的变化率与激发载流子浓度，激发光子能量的依赖关系，全面理解不同的参数对自旋相关透射/反射率的影响，并将模拟结果和相关实验数据进行比较。其研究成果可以为抽运探测透射/反射光谱提供理论基础，并解释自旋动力学实验研究观察到的复杂现象。

本项目成功模拟了半导体体材料在带隙附近、高载流子浓度下，电子自旋对抽运探测反射光谱的影响。考虑自旋相关的带填充效应、带隙重整效应，以InP，GaAs单晶为例，建立反射率的变化率与激发光子能量的依赖关系；结果发现在带隙附近反射率的变化率对激发载流子浓度极其敏感，随着光子能量的增加，反射率的变化率由漂白变为吸收，利用模拟结果拟合实验数据，符合较好。利用二能级系统速率方程，在小信号近似的条件下，模拟了反射率的演变曲线，并利用此结果拟合了CdTe单晶的自旋动力学过程。本项目的结果为圆偏振抽运探测反射光谱技术提供了理论依据，并利用获得的结果解释了相关实验现象。