Ultra-fast solid-state switching based on tunneling-assisted delayed breakdown device (TADBD)

Tunneling-assisted impact ionization fronts in semiconductors recently investigated theoretically by Rodin et al are expected to be much faster and generate higher plasma concentrations in comparison with the traditional impact ionization. We have conducted experiments and numerical simulations of this new switching process. In experiments with double-stage sharpening scheme overvoltage across tested tunneling-assisted delayed breakdown device (TADBD) was equal to about 10 kV/ns per one structure. TADBD included 20 series connected semiconductor structures with 0.25-cm² surface area. The length of the stack was 9 mm. The triggering occurred after a delay of about 1 ns, when the reverse electric field of ∼1 MV/cm was reached across the structures. We have obtained output pulses having 150-kV amplitude across a 50-Ω external load with about 200-ps rise time. Maximum current density in the TADBD was ∼13 kA/cm². The maximum rise rates of the current and the voltage were 10 kA/ns and 500 kV/ns respectively. In numerical simulations real dopant distribution profile of the semiconductor structure was taken into account. Numerical simulations showed that the triggering occurred after a delay of 1 ns, when the threshold of tunneling ionization of 1 MV/cm was reached in vicinity of p-n junction. Tunneling-assisted impact ionization fronts pass through the structure in both directions from p-n junction within approximately 60 ps, filling it with electron-hole plasma having a concentration of about 10¹⁷ cm^-3. The total velocity of the front´s propagation is about 20 times higher than the saturated velocity of the carriers.