S type current/voltage characteristics and recombination emission in Gunn diodes

When impact ionisation occurs in Gunn diodes, recombination radiation must exist with photon energy less than the energy gap due to the Franz-Keldysh effect in the high-field domain. This radiation must be polarised along the field. The criterion for stimulated emission in the Gunn diode is derived. Stimulated emission takes place only outside the high-field domain and can be modulated with the frequency of the Gunn generation.