DONOR IMPACT IONIZATION AND ELECTRON HEATING IN A GAAS/ALXGA1-XAS SUPERLATTICE

Impact ionization of donors in a GaAs/AlxGa1-xAs superlattice is observed when an electric field above a threshold value is applied parallel to the growth direction. Impact ionization arises from the electric field-induced heating of electrons in the superlattice to energies above the donor binding energy. The threshold electric field for impact ionization is a strong function of magnetic field which is applied parallel to the current. The effect of the magnetic field is to increase the donor binding energy which then requires higher energy electrons and, correspondingly, higher electric fields for impact ionization. The electric field dependence of the mean electron energy is gleaned from the impact ionization data. We find that the electrons are heated well above the predicted miniband width of the superlattice which indicates that the transport proceeds by resonant tunneling between lifetime-broadened quantum levels. © 1990.