Impact ionization fronts in Si diodes: Numerical evidence of superfast propagation due to nonlocalized preionization

TL;DR

This paper provides numerical evidence of superfast impact ionization fronts in high-voltage silicon diodes, driven by nonlocalized preionization and propagating at velocities up to ten times the saturated drift speed.

Contribution

It introduces a novel propagation mode for impact ionization fronts in silicon diodes, characterized as a pulled front driven by nonlocalized preionization, with detailed numerical analysis.

Findings

Two ionizing fronts propagate in opposite directions.

Front velocities reach up to 10 times the saturated drift velocity.

Preionization is caused by field-enhanced emission from deep-level impurities.

Abstract

We present numerical evidence of a novel propagation mode for superfast impact ionization fronts in high-voltage Si $p^+$-$n$-$n^+$ structures. In nonlinear dynamics terms, this mode corresponds to a pulled front propagating into an unstable state in the regime of nonlocalized initial conditions. Before the front starts to travel, field-ehanced emission of electrons from deep-level impurities preionizes initially depleted $n$ base creating spatially nonuniform free carriers profile. Impact ionization takes place in the whole high-field region. We find two ionizing fronts that propagate in opposite directions with velocities up to 10 times higher than the saturated drift velocity.