基于非线性效应的半导体载流子超快动力学研究

In this program, a modified ultrafast time-resolved pump-probe system is used to investigate the transient nonlinear absorption and refraction in semiconductors simultaneously under single X-ray.excitation, which allows us to evaluate the process induced by carrier dynamic variety more comprehensively. The main contents include: Investigate the dynamics process of carrier refraction and absorption in semiconductors under pulse laser excitation. Determine the nonlinear kinetics of carrier lifetime absorption cross-section and other crucial parameters. Analysis the impact of various physical mechanisms on carrier dynamics. Study the impact of doping ratio on nonlinear optical parameters in semiconductors, such as carrier density and response time. Find a way to reduce the nonlinear response time. Search for proper method to investigate the ultrafast response of materials in X-ray region, research the ultrafast carrier dynamic of semiconductors excited by intensive X-ray pulse, propose an optimization scheme of material design, find a possible approach to all optical X-ray detection device with high speed and low threshold.

本项目拟在单发X射线脉冲作用下，利用改进的超快时间分辨系统实现半导体瞬态非线性吸收及非线性折射的同时测量，可更全面的研究载流子动态变化引起过程。主要研究内容包括：在脉冲激光的激发下，研究半导体材料中载流子折射与吸收的动力学过程，从而确定载流子寿命、吸收截面等重要参量的非线性变化过程，并分析影响载流子动力学过程的各项物理机理。研究半导体材料掺杂比对载流子瞬态浓度、时间响应速度等非线性参数的影响，确定提高材料时间响应的方法。探索在单发X射线脉冲作用下测量材料非线性时间响应特性的方法，研究强X射线脉冲作用下半导体材料载流子动力学的变化过程，提出材料优化设计方案，开展高速、低阈值的全光X射线探测器件的研究。

针对“培育项目”中的明确目标项目-70基于非线性效应的半导体载流子动力学研究开展了本项目的研究。首先利用阶梯延时反射镜使探测光产生不同时间延迟的脉冲序列，结合泵浦光完成了单脉冲泵浦探测系统的建立。通过对阶梯延时反射镜的不断改进，设计出了能产生延迟时间较长的阶梯阵列延时反射镜，确定了单发X射线脉冲的泵浦探测系统的实施方案。利用超快时间分辨系统完成了不同半导体瞬态非线性的测量，通过对半导体材料中载流子光学非线性的动力学过程的研究，确定了载流子寿命、吸收截面等重要参量，并分析影响载流子动力学过程的各项物理机理。为了探索提高材料时间响应的方法，研究了半导体材料掺杂比对载流子瞬态浓度、时间响应速度等非线性参数影响的规律。