1 Department of Photonics Engineering, Technical University of Denmark2 Nanophotonics Theory and Signal Processing, Department of Photonics Engineering, Technical University of Denmark3 Max Planck Institute4 Fibers & Nonlinear Optics, Department of Photonics Engineering, Technical University of Denmark
In a series of systematic optical pump–terahertz probe experiments, we study the density-dependent electron scattering rate in photoexcited GaAs in the regime of strong carrier diffusion. The terahertz frequency-resolved transient sheet conductivity spectra are perfectly described by the Drude model, directly yielding the electron scattering rates. A diffusion model is applied to determine the spatial extent of the photoexcited electron-hole gas at each moment after photoexcitation, yielding the time-dependent electron density, and hence the density-dependent electron scattering time. We find that the electron scattering time decreases from 320 to 60 fs, as the electron density changes from 1015 to 1019 cm−3.