Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan.
Institute for Molecular Science, 38 Nishigonaka, Myodaiji, Okazaki 444-8585, Japan.
Sci Rep. 2017 Jan 11;7:40492. doi: 10.1038/srep40492.
In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [ΔR(ω)/R(ω)] with the Drude model in the 200-5000 cm region, the time-dependent plasma frequency and scattering rate have been obtained. Through the calculation, we can further get the time-dependent photoexcited carrier concentration and carrier mobility. The Auger recombination essentially dominates the fast relaxation of photoexcited carriers within 100 ps followed by slow relaxation due to diffusion. Additionally, a novel oscillation feature is clearly found in time-resolved difference reflection spectra around 2000 cm especially for high pump fluence, which is the Lorentz oscillation lasting for about 20 ps due to the Coulomb force exerted just after the excitation.
在这项研究中，我们在块状 Ge 中进行了 800nm 泵浦和超宽带中红外（MIR）探针光谱学，具有高时间分辨率（70fs）。通过在 200-5000cm 区域内用 Drude 模型拟合时间分辨的差示反射光谱 [ΔR(ω)/R(ω)]，得到了随时间变化的等离子体频率和散射率。通过计算，我们可以进一步得到随时间变化的光激发载流子浓度和载流子迁移率。俄歇复合在 100ps 内基本上主导光激发载流子的快速弛豫，随后由于扩散而出现缓慢弛豫。此外，在时间分辨差示反射光谱中，特别是在高泵浦强度下，明显发现了一个新的振荡特征，大约在 2000cm 处，这是由于激发后立即施加的库仑力引起的洛伦兹振荡，持续约 20ps。
