Ultrabroadband Midinfrared Pump-Probe Spectroscopy of Germanium
Tien-Tien Yeh1*, Hideto Shirai2, Chien Ming Tu1, Yutaka Nomura2, Chih-Wei Luo1, Takao Fuji2, Takayoshi Kobayashi1,3
1Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
2Institute for Molecular Science, Okazaki, Japan
3Advanced Ultrafast Laser Research Center, The University of Electro-Communications, Tokyo, Japan
* presenting author:Tien-Tien Yeh, email:jiljiljilji@gmail.com
In this study, we carried out the 800-nm pump and ultrabroadband mid-infrared (MIR) spectroscopy with high time-resolution in Ge. By fitting with the reflectivity change transients in the region from 200 to 5000 cm-1 with Drude model, the time-dependent photoexcited carrier mobility, plasma frequency, scattering rate, and carrier concentration have been obtained. The Auger recombination essentially dominates the fast relaxation processes of photoexcited carriers within 100 ps; meanwhile, the slow relaxation process is dominated by the diffusion effect. Additionally, a novel oscillation feature is unambiguously found in time-dependent reflectance around 2000 cm-1 especially for high pump fluences, which is due to the Lorentz oscillation with the Coulomb force within 20 ps.

Keywords: sumiconductor, optics, mid-infrared