title: Ultrafast carrier dynamics in Ge by ultra-broadband mid-infrared probe spectroscopy.
abstract: 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-1region, 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-1especially for high pump fluence, which is the Lorentz oscillation lasting for about 20 ps due to the Coulomb force exerted just after the excitation.
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan.
authors.forename: Tien-Tien
authors.initials: TT
authors.lastname: Yeh
authors.affiliation: Institute for Molecular Science, 38 Nishigonaka, Myodaiji, Okazaki 444-8585, Japan.
authors.forename: Hideto
authors.initials: H
authors.lastname: Shirai
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan.
authors.forename: Chien-Ming
authors.initials: CM
authors.lastname: Tu
authors.affiliation: Institute for Molecular Science, 38 Nishigonaka, Myodaiji, Okazaki 444-8585, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Fuji
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan.|Advanced Ultrafast Laser Research Center, and Department of Engineering Science, Faculty of Informatics and Engineering, University of Electro-Communications, 1-5 1 Chofugaoka, Chofu, Tokyo 182-8585, Japan.
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan.
authors.forename: Chih-Wei
authors.initials: CW
authors.lastname: Luo