Instabilities during high-field electrical conduction in solids

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Abstract
Measurements of the time and voltage dependence of dc and ac currents in insulators and semiconductors and the evaluation of results of other authors on corresponding measurements using metallic samples reveal that critical power densities Nk1≈10−8 W/mm3 and Nk2≈10−5 W/mm3 separate three different ranges of charge transport loading of solids in the frequency range 0⩽f⩽50 Hz. The loading state of a solid is described macroscopically by the average electric power density and microscopically by the local value of the power density j↘⋅E↘. In semiconductors and insulators electrical breakdown or transition to a strongly localized and highly conducting state is unavoidable if an overcritical power density N≳10−5 W/mm3 is supplied. This locally quite limited and highly conducting state exists in the prebreakdown range wherein Nk2<N<Nfusion. It is related to the Ovshinsky effect in amorphous semiconductors. Usually the current density, continuity, and Poisson equations are used to describe charge transport within a solid. In order to complete this description it is proposed that power density N=j↘⋅E↘ must be considered.