Impact ionization in low-band-gap semiconductors driven by ultrafast THz excitation: beyond the ballistic regime

TL;DR

This study uses ultrafast THz spectroscopy and modeling to explore impact ionization in low-gap semiconductors, revealing carrier multiplication factors exceeding 10 at high fields, beyond ballistic dynamics.

Contribution

It demonstrates impact ionization effects in InSb under high-field THz excitation, extending understanding beyond previous quasi-ballistic models with new spectral and temporal insights.

Findings

Impact ionization observed at fields above 60 kV/cm

Carrier multiplication factor exceeds 10 at highest fields

Numerical model accurately reproduces impact ionization dynamics

Abstract

Using two-dimensional THz spectroscopy in combination with numerical models, we investigate the dynamics linked to carrier multiplication caused by high-field THz excitation of the low-gap semiconductor InSb. In addition to previously observed dynamics connected with quasi-ballistic carrier dynamics, we observe other spectral and temporal features that we attribute to impact ionization for peak fields above 60 kV/cm, which continue up to the maximum investigated peak field of 430 kV/cm. At the highest fields we estimate a carrier multiplication factor greater than 10 due to impact ionization, which is well-reproduced by a numerical simulation of the impact ionization process which we have developed.