Recombination and impact-ionization peculiarities in many-valley semiconductors

Investigations were performed for n-type Si at 27 K in the presence of heating electric and strong magnetic fields taking the anisotropy of the effective mass and additionally of the carrier scattering time on acoustic phonons properly into account. This consideration of the many-valley band structure and the consequent intervalley repopulation yields very significant dependences of mean carrier velocities, recombination at shallow donors, as well as their impact-ionization and intervalley scattering times on the orientations of the applied fields. The calculated change of the carrier concentration with heating exhibits N- and S-type behavior for certain field orientations, and the numerically obtained current-voltage characteristics in the absence and presence of magnetic fields agree well with the experimentally determined ones.