Lone-pair states as a key to understanding impact ionization in chalcogenide semiconductors

Impact ionization of holes and domination of p-conductivity in chalcogenide semiconductors are attributed to a weak electron-phonon interaction inherent to lone-pair states. This argument is supported by first-principles calculations of an acoustical deformation potential in trigonal selenium. Results of the calculations reveal a strong dependence of the deformation potential on the excess energy of charge carriers. The latter is interpreted using a simple tight-binding model.