Electron-Electron Interaction in Hot Electron Problems

The behaviours of warm and hot electorons in n-type germanium at 77°K are investigated theoretically. The following assumptions are adopted: (1) Electrons are not degenerate, (2) the shape of the energy surface is spherically symmetric, (3) electrons are scattered by acoustic and optical modes of vibrations, and by ionized impurity centers and (4) the electron-electron interaction is taken into account by the Fokker-Planck approximation. The results are compared with Gunn's recent experiments. We find that the Maxwellian distribution function with the electron temperature does not give a good agreement with experiment when the impurity density is low. On the other hand, the electron-electron interaction works decisively in reducing the electron distribution to the Maxwellian form when the impurity density is high. The critical density seems to lie near 1015/cm3 at 77°K.