Recombination Processes following Impact Ionization by High-Field Domains in Gallium Arsenide

Abstract

When a field greater than that required to produce Gunn instabilities is applied to gallium arsenide containing free electrons in concentrations of 1017 cm−3 or more, excess current rather than current saturation is seen. Impact ionization due to high-field domains causes a substantial increase in carrier density. The processes involved in the generation and recombination of these excess carriers are analyzed here. Recombination occurs by competing radiative and nonradiative mechanisms, with long-term trapping also playing a role. Measurements of the time dependence of excess conductivity and recombination radiation, the spectral distribution of the radiation, and its intensity as a function of excess carrier concentration, allow the generation rate and recombination cross sections to be deduced. The generation rate is consistent with that expected from flat-topped domains. Cross sections for the capture of both holes and electrons by the recombination centers dominant under these conditions are of the order 10−17 cm2. The emitted radiation is strongly self-absorbed; correction for this factor shows that most of the original emission has energy greater than the bandgap. The direct recombination cross section is deduced to be near 5×10−18 cm2, which is in reasonable agreement with that derived from the van Roosbroeck-Shockley theory.