THz-pump -- THz-probe spectroscopy of semiconductors at high field strengths

TL;DR

This study uses ultrafast THz pump-probe spectroscopy to investigate high-field carrier dynamics in GaAs and InSb, revealing free carrier absorption saturation, impact ionization, and carrier cooling processes at room and cryogenic temperatures.

Contribution

It demonstrates a THz-pump/THz-probe method that isolates carrier dynamics without optical electron-hole generation, providing clearer insights into high-field semiconductor behavior.

Findings

Observation of free carrier absorption saturation at high THz intensities

Detection of impact ionization in InSb when energy exceeds bandgap

Monitoring of carrier cooling dynamics in GaAs

Abstract

Pumping n-type GaAs and InSb with ultrafast THz pulses having intensities higher than 150 MW/cm2 shows strong free carrier absorption saturation at temperatures of 300 K and 200 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.