Excitation-density and excess-energy dependence of ultrafast dynamics of photoexcited carriers in intrinsic bulk CdTe
Excitation-density and excess-energy dependence of ultrafast dynamics of photoexcited carriers in intrinsic bulk CdTe
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本征体 CdTe 中光生载流子超快动力学的激发密度和过剩能量依赖性
DOI：
10.1016/j.rinp.2021.105047
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发表时间：
2021-11
影响因子：
5.3
通讯作者：
Huizhen Wu
中科院分区：
文献类型：
--
作者：
Yicun Chen;Tianyu Shu;Tianshu Lai;Huizhen Wu
本文利用飞秒分辨的泵浦-探测暂态微分透射谱，深入系统地研究了本征CdTe薄膜中光激发载流子的超快动力学随载流子密度和超额能量的变化规律。在直接带隙半导体的带间跃迁吸收模型的基础上，通过引入光激载流子的热化、冷却和复合动力学，建立了直接带隙半导体的带间跃迁吸收模型。然后，利用该模型对测量的超快动力学进行了最佳拟合，以求取加热电子的初始温度以及热化、冷却和复合动力学过程的时间常数作为载流子密度和过剩能量的函数。热化时间常数随载流子浓度的增加而增大，随过剩能量的减小而减小，表明光激载流子的热化过程主要受载流子-声子散射的影响。我们首次发现，热化载流子的冷却强烈依赖于载流子浓度和过剩能量，冷却时间常数在0.2-5微秒的较大范围内变化。研究还发现，本征CdTe薄膜中的载流子复合主要是电子-空穴对的辐射复合，而不是以往报道的掺杂CdTe薄膜中的俄歇复合。这些新的结果对于理解光激发载流子弛豫过程的微观机制和应用于基于CdTe的光电子器件具有重要意义。
In this study, ultrafast dynamics of photoexcited carriers in an intrinsic CdTe film are investigated deeply and systematically as a function of carrier density and excess energy using femtosecond-resolved pump–probe transient differential transmission spectroscopy. A dynamic model is developed based on an interband transition absorption model in direct bandgap semiconductors by introducing the dynamics of thermalization, cooling and recombination of photoexcited carriers into the interband transition absorption model. Then, the model is used to best fit the measured ultrafast dynamics to retrieve the initial temperature of thermalized electrons and time constants of the thermalization, cooling and recombination dynamic processes as a function of carrier density and excess energy. The increase with carrier density and the decrease with excess energy of thermalization time constant reveal that thermalization process of photoexcited carriers is dominated by carrier-phonon scatterings. We find for the first time that cooling of thermalized carriers depend strongly on carrier density and excess energy, and cooling time constant varies in a wide range from 0.2 to 5 ps. It is also found that carrier recombination in the intrinsic CdTe film is dominated by the radiative recombination of electron-hole pairs, rather than Auger recombination as reported in doped CdTe films. These new results are very important to understanding of microscopic mechanism of relaxation processes of photoexcited carriers and applications of CdTe-based optoelectronic devices.