Impact ionization in InSb probed by terahertz pump-terahertz probe spectroscopy

Picosecond carrier dynamics in indium antimonide (InSb) following excitation by below band gap broadband far-infrared radiation was investigated at 200 and 80 K. Using a THz-pump/THz-probe scheme with pump THz fields of 100 kV/cm and an intensity of 100 MW/cm(2), we observed carrier heating and impact ionization dynamics. The number of carriers produced exceeds 10(16) cm(-3), corresponding to a change in carrier density Delta N/N of 700% at 80 K. The onset of a well-defined absorption peak at 1.2 THz is an indication of changes in longitudinal optical (LO) and longitudinal acoustic (LA) phonon populations due to cooling of the hot electrons.