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

In this paper, we reveal the intricate interplay between two major nonlinear terahertz (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 the THz strength of 91 kV/cm, is the critical field where the bleaching of absorption (induced by intervalley scattering of electrons in the conduction band) is dominant below this field, whereas above it impact ionization starts to be the dominant energy loss mechanism. The temporal and amplitude change of the total average effective carrier mass and the total carrier density allow us to monitor the THz strength fields where each scattering effect plays a dominant role. We find that the change in the carrier populations is not the only factor that influences the current density, but indeed the average drift velocity of each valley is also a decisive factor, which is derived from the carrier momentum change. The developed theoretical model match very well qualitatively and quantitatively with the experimental results.