Tunneling-assisted impact ionization fronts in semiconductors

ionization; impact ionization fronts; front propagation;We propose a novel type of ionization front in layered semiconductorstructures. The propagation is due to the interplay ofband-to-band tunneling and impact ionization.Our numerical simulations show that the front can be triggered when an extremely sharp voltage ramp ($sim 10$kV/ns)is applied in reverse direction to a Si $p^+-n-n^+ $ structure that is connected in series with an external load. The triggering occurs after a delay of 0.7 to 0.8 ns.The maximal electrical field at the front edge exceeds $10^6$V/cm. The front velocity $v_f$ is 40 times faster thanthe saturated drift velocity $v_s$.The front passes through the n-base with a thickness of 100 mu m within approximately 30~ps,filling it with dense electron-holeplasma. This passage is accompanied by a voltage drop from8~kV to dozens of volts. In this way a voltage pulsewith a ramp up to 500, kV/ns can be appliedto the load. The possibility to form a kilovolt pulse with sucha voltage rise rate sets new frontiers in pulse power electronics