Tunneling ionization in high-frequencyfields as well as in static fields is suggested as a method for the
characterization of deep impurities in semiconductors. It is shown that an analysis of the field and temperature
dependences of the ionization probabilityallows to obtain defect parameters like the charge of the impurity, tunneling times, the Huang–Rhys parameter, the difference between optical and thermal binding energy and the basic structure of the defect adiabatic potentials. Compared to static fields, high-frequencyelectric fields in the terahertz-range offer various advantages, as theycan be applied contactlesslyand homogeneouslyeven to bulk samples using the intense radiation of a high-power pulsed far-infrared laser.