Filamentation in Optically Controlled Semiconductor Switches

Abstract

In recent years, current filamentation has been identified as an important mode of failure in optically controlled semiconductor switches, preventing the hold-off voltage of the devices to reach its theoretical (material-dependent) limit. While considerable progress has been made in describing the phenomenological features of this process, little is still known about the mechanisms that responsible for it in the first place. In this paper we investigate the role of two normally overlooked effects, namely that of magneto-constriction ("pinching") and of multi-impact ionization of deep traps. Extending earlier work on this matter [l], we show that a combination of the two effects may indeed give rise to dynamic phenomena which qualitatively resemble the observed processes. A quantitative evaluation, however, shows that the processes ~ while indeed important for filamentation ~ are not dominant enough to explain the documented time scales by itself.

<title>Self-consistent 2D simulations of filament propagation in photoconducting switches</title>

“…A region of space charge tries to relax under the action of its self-consistent electrostatic field; if the time step is too large, the motion over-compensates generating an oppositely directed field of larger magnitude. The stability requirement for explicit differencing is that the resistive decay time be resolved, At<r 'rr (5) For intrinsic GaAs at 300 K (u=8.OxlO3 cm2/V-s), the resistive decay time is approximately 'r=(86O s/cm3)/ne. In the high density, low-field region of the filament this limit can be a serious constraint.…”