Experimental observation of delayed impact-ionization avalanche breakdown in semiconductor structures without $p$–$n$ junctions

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.