Bipolar Gunn Effect and Subnanosecond Switching of the High-Voltage GaAs Diodes Initiated by Microsecond Kilovolt Voltage Ramp

It is well known that GaAs diodes of various design such as S-diodes with deep levels and pulse avalanche diodes exhibit subnanosecond transient from blocking to conducting state. Recently the mechanism of such switching was explained by formation of ionizing Gunn domains. The switching occurs in narrow current filaments with extreme ∼ 1 MA/cm ² ) current density that is required for formation of ionizing Gunn domains. Hence filamentation is a necessary condition for subnanosecond switching. The filamentation mechanism is usually attributed to the structural imperfections or surface breakdown. In this paper we demonstrate that subnanosecond switching is possible for an ideal diode without any imperfections, or deep levels that are present in S-diodes. It also does not require a steep voltage ramp as in the case of pulse avalanche diodes. This universal switching scenario is based on inherent features of GaAs diodes and includes (i) formation of spatially uniform state with double avalanche injection, (ii) current filamentation due to negative differential conductance of the state with double avalanche injection and (iii) subnansecond switching due to appearance of ionizing Gunn domains in current filaments. We illustrate this scenario by two-dimensional numerical simulations of the simplest $p-i-n$ diode structure with 1.4 kV breakdown voltage. The triggering is initiated by a kilovolt pulse with microsecond front and reverse polarity applied to the diode and in-series $50-\Omega$ load. The diode exhibits 500 ps transient to the conducting state with 100 V residual voltage and forms 30 A amplitude pulse in the load.