The contribution of free electrons to the dielectric function is largely determined by their plasmonic resonance, a collective density oscillation. We studied this broadband and carrier-density-dependent response in the narrow-gap semiconductor InSb with THz shockwave spectroscopy. A synthesized waveform, with a steep onset followed by a short electric-field plateau, gives access to a multioctave spectrum of frequencies from 100 GHz up to the mid infrared. By measuring the entire spectral characteristics of the plasma, we analyze the dynamics of photogenerated free electrons for a wide range of excitation fluences. Thanks to this analysis, we were able to quantify the coefficients of both electron trapping and the Auger process from cryogenic to room temperature.

• Received 11 April 2022
• Revised 5 October 2022
• Accepted 12 October 2022

DOI:https://doi.org/10.1103/PhysRevB.106.205201