Spatiotemporal modes of fast avalanche switching of high-voltage layered semiconductor structures: From subnano to picosecond range

Abstract

The effect of delayed impact ionization breakdown initiated in high-voltage Si or GaAs p+nn+ diode by a steep voltage ramp leads to 100 ps avalanche transient from blocking to conducting state. Here, we demonstrate that qualitatively different inner mechanisms—or spatiotemporal modes—can be responsible for superfast high-voltage avalanche switching. The well-known mechanism based on TRApped Plasma Avalanche Triggered Transit (TRAPATT)-like ionizing front passage is compared with three novel spatiotemporal switching scenarios. The first of these novel modes corresponds to a new type of ionizing front travelling across the structure faster than the saturated drift velocity. Another corresponds to the quasiuniform avalanche breakdown of the whole n base. The last one—the “back-stroke” mode—takes place when switching occurs only in the part of the device cross section. For these novel modes, the calculated switching time (tens of picoseconds) is several times smaller than for well-known TRAPATT-like front (∼100 ps). We analyze all four spatiotemporal modes in their connection with the device structural parameters. By means of numerical simulations, we demonstrate that varying only one parameter of a p+nn+ structure—the n base dopant concentration—it is possible to completely change the inner dynamics. Our analysis reveals that subnanosecond—100 ps or less—switching time may be determined either by the ionizing front passage time or by the internal “discharge” time of the device via generated electron–hole plasma.