Breakdown damages of photoconductive silicon at high fields

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Abstract
Different types of damages induced in photoconductive silicon at high fields are discussed on the basis of the corresponding physical processes developed in the semiconductor - ambient dielectric system. Catastrophic damages produced at high fields by surface flashover or total bulk breakdown are compared with surface filaments developed in certain conditions in the prebreakdown stage. A physical mechanism of nonohmic conduction inducing surface filaments is proposed. A new high field limitation, well before total breakdown, is defined in the dark condition by the onset field of the nonohmic regime. Below this field the device operation is safe and stable, while beyond this limit, a surface filament, distinctly different from the surface flashover tracks, may appear on the surface of the device, permanently degrading the device quality. Along with the surface filaments, contact damages may also appear in the device in this nonohmic regime. The semiconductor damages are observed using SEM and optical micrographs. The mechanisms leading to these damages are discussed using electrical and optical characteristics at high fields, as well as the localization of light emissions. The practical importance of the new nondamaging high field limitation is discussed.

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