Non-avalanche dielectric breakdown in wide-band-gap insulators at DC and optical frequencies

Abstract

It is the purpose of this paper to put recent novel experimental efforts to understand dielectric breakdown in wide-band-gap materials in various fields into a common framework and outline significant changes in the understanding of dielectric breakdown at optical frequencies and free electron heating under DC conditions. New experimental techniques used to measure multiphoton absorption and energy deposition in wide-bandgap alkali halides in the prebreakdown regime have led to hard evidence refuting the avalanche model of laser-induced damage at visible laser wavelength. The experiments show that virtually all lattice heating occurs via nonlinear absorption of laser photons by multiphoton excited free electrons. Direct measurements of free electron heating by DC fields in thin SiO2-films and direct measurements of electron-phonon scattering rates of energetic free electrons impose a new understanding of carrier heating. The scattering of free electrons with non-polar acoustic phonons is found to be the dominant interaction in preventing the free carriers from reaching energies high enough to cause impact ionization and initiate avalanche breakdown. These results unambiguously show that the role of avalanche breakdown under DC conditions has been overestimated in the past.