We have experimentally studied the dynamics of impact-ionization switching in semiconductor structures without p – n junctions when subnanosecond high-voltage pulses are applied. Silicon n ^+– n – n ^+ type structures and volume ZnSe samples with planar ohmic contacts exhibit reversible avalanche switching to the conducting state within about 200 ps, which resembles the well-known phenomenon of delayed avalanche breakdown in reverse-biased p ^+– n – n ^+ diode structures. Experimental data are compared to the results of numerical simulations.

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