THz-pump/THz-probe spectroscopy of semiconductors at high field strengths [Invited]

Pumping n-type GaAs and InSb with ultrafast THz pulses having intensities higher than $150\mathrm{MW}∕{\mathrm{cm}}^2$ shows strong free-carrier absorption saturation at temperatures of $300\mathrm{K}$ and $200\mathrm{K}$, respectively. If the energy imparted to the carriers exceeds the bandgap, impact ionization processes can occur. The dynamics of carrier cooling in GaAs and impact ionization in InSb were monitored using THz-pump/THz probe spectroscopy, which provides both sub-bandgap excitation and probing, eliminating any direct optical electron-hole generation that complicates the evaluation of results in optical pump/THz probe experiments.