Interplay between intervalley scattering and impact ionization induced by intense terahertz pulse in InSb thin films

In this work, we reveal the intricate interplay between two major nonlinear THz effects: intervalley scattering and impact ionization, generated by an intense few-cycle THz pulse in an undoped (100) indium antimonide semiconductor at room temperature. Our results show an initial transmission enhancement when increasing the peak electric field up to 91 kV/cm, followed by increased absorption for higher fields. Our analytical model explains that this initial transmission enhancement occurs due to a balance between absorption bleaching (induced by intervalley scattering of electrons in the conduction band) and impact ionization. We show that for THz peak electric fields higher than 91 kV/cm, impact ionization starts to be the dominant energy loss mechanism. These experimental results match very well qualitatively and quantitatively with our developed theoretical model.