Wang Lijie, Xu Yafeng, Mohammed Omar F
Center for Renewable Energy and Storage Technologies, Division of Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
J Phys Chem Lett. 2025 Jul 3;16(26):6698-6703. doi: 10.1021/acs.jpclett.5c01609. Epub 2025 Jun 23.
Accurately interpreting ultrafast carrier dynamics in solid-state materials requires understanding the distinct contributions of absorption and refractive index variations to transient optical responses. In this study, we systematically disentangle temperature-induced changes in the absorption coefficient and refractive index of silicon crystals as a model system. Our approach utilizes transient reflection spectroscopy, complemented by in situ temperature-dependent spectroscopic ellipsometry and density functional theory (DFT) calculations. We examine and decipher the observed spectral shifts and profile modifications in correlation with lattice expansion from 298 to 403 K. Our findings reveal that thermal-induced variations in the refractive index account for approximately 85% of the transient reflection signal at 0.2 ps in the visible range, rising to about 93% at 10 ps. This behavior is attributed to temperature-driven modifications in the band structure at the Γ and X points, inducing significant changes in the dielectric function. These changes distinctly impact absorption and refractive index, each exhibiting unique spectral signatures and temporal behaviors. This work establishes a framework for decoupling optical parameters in transient measurements, providing valuable insights for the study of solid-state optoelectronic materials.
准确解释固态材料中的超快载流子动力学需要理解吸收和折射率变化对瞬态光学响应的不同贡献。在本研究中，我们以硅晶体为模型系统，系统地解析了温度引起的吸收系数和折射率变化。我们的方法利用瞬态反射光谱，并辅以原位温度相关的光谱椭偏仪和密度泛函理论（DFT）计算。我们研究并解读了在298至403 K温度范围内与晶格膨胀相关的观测到的光谱位移和轮廓变化。我们的研究结果表明，在可见光范围内，热致折射率变化在0.2 ps时约占瞬态反射信号的85%，在10 ps时升至约93%。这种行为归因于温度驱动的Γ点和X点能带结构的变化，导致介电函数发生显著变化。这些变化对吸收和折射率有明显影响，各自表现出独特的光谱特征和时间行为。这项工作建立了一个在瞬态测量中解耦光学参数的框架，为固态光电子材料的研究提供了有价值的见解。
