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

Picosecond carrier dynamics in indium antimonide (InSb) following excitation by below-bandgap broadband far infrared radiation were investigated at 200 K and 80 K. Using a novel 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. The number of carriers produced exceeds 10^16 cm-3, corresponding to a change in carrier density Delta N/N of 700% at 80K. The onset of a well defined absorption peak at 1.2 THz is an indication of changes in LO and LA phonon populations due to cooling of the hot electrons.