Breakdown space charge

A few remarks are due about this feature. The nonuniformity above is a formal expression of breakdown of the local electro-neutrality assumption in concentration polarization, described in the previous chapter. Essentially, this reflects the failure of a description based upon assuming the split of the physical region into a locally electro-neutral domain and an equilibrium double layer where all of the space charge is concentrated. The source of this failure, reflected in the nonuniformity of the corresponding matched asymptotic expansions, is that the local Debye length at the interface tends to infinity as the voltage increases. In parallel a whole new type of phenomena arises, which is not reflected in the simplistic picture above. The... 

The field required for breakdown to occur and the mode of breakdown depend on doping level. As the dopant concentration increases, the width of the space charge layer decreases and the probability of tunneling increases rapidly so that Z mr breakdown becomes more likely than avalanche breakdown. Zener breakdown is, in general, involved in the electrode processes on p and n materials under a reverse bias. 

Pulsed electron irradiations are usually conducted with accelerators charged from 0.1 to 6.0 MeV, and pulse durations range from 3 to 60 nsec. The explosives are pressed pellets with thicknesses of about 0.2 of the electron range. If the samples are too thick, the electrons will be trapped in the material causing a nonuniform dose. Further, the resulting space charge causes dielectric breakdown. and initiation is caused by electric discharge rather than by absorbed radiation. 

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