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

Abstract

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.

Interaction of hot carriers with optical phonons in Selenium

“…2b). Similar observations were made for an acoustical phonon deformation potential [13]. The weak response of upper valence states to lattice perturbation has been attributed to the fact that the lone-pair states are not involved in hybridization, as opposed to the states in the conduction band [13].…”

“…This result is attributed to the weak coupling of lone-pair states to perturbations associated with optical vibrational modes and interpreted along the line of a simple tight-binding model proposed in Ref. [13]. Since the scattering rate is proportional to the square of the corresponding matrix element, the energy relaxation time due to the emission of optical phonons for holes is expected to be longer than that for electrons.…”

First-principle prediction of single-carrier avalanche multiplication in chalcopyrite semiconductors

“…In conjunction with the week electron-phonon coupling inherent to holes in t-Se [15,23], these properties favor the single-carrier impact ionization.…”

Single-carrier impact ionization favored by a limited band dispersion

“…The results of our calculations suggest that the suppression of electrons' avalanche multiplication in t-Se can be caused by peculiarities of its electronic structure. In conjunction with the week electron-phonon coupling inherent to holes in t-Se [15,23], these properties favor the single-carrier impact ionization. Amorphous Selenium also reveals a high disparity between impact ionization coefficients for electrons and holes.…”