Localized temporary increase in material conductivity following impact ionization in a Gunn-effect domain

It has been found that raising the applied bias on a long sample containing a high-field domain can result in a temporary increase in material conductivity over the region of the sample traversed by the domain while the higher bias was applied. The effect can be explained in terms of intrinsic impact ionization within the domain in the presence of a deep impurity level. The measured decay time of the "memory" is consistent with a capture cross section of about 10^-15cm², for electrons at the deep level, indicating that the empty center is neutral. Conversely, the filled center will have a high capture cross section for holes. Following intrinsic impact ionization in the domain the mechanism is believed to involve the rapid capture of holes at the filled centers and a subsequent relatively slow return of the extra electrons to the empty centers. The deep impurity level is thus responsible for fixing the memory in position in the material and also for inhibiting the emission of recombination radiation during impact ionization.