Tunneling-assisted impact ionization fronts in semiconductors

We discuss a type of ionization front in layered semiconductor structures. The propagation is due to the interplay of band-to-band tunneling and impact ionization. Our numerical simulations show that the front can be triggered when an extremely sharp voltage ramp (∼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 106 V/cm. The front velocity vf is 40 times faster than the saturated drift velocity vs. The front passes through the n-base with a thickness of 100 μm within approximately 30 ps, filling it with dense electron–hole plasma. This passage is accompanied by a voltage drop from 8 kV to a voltage in the order of 10 V. In this way a voltage pulse with a ramp up to 500 kV/ns can be applied to the load. The possibility to create a kilovolt pulse with such a voltage rise rate sets new frontiers in pulse power electronics.