Injection-Limited and Space-Charge-Limited Conduction in Wide Bandgap Semiconductors with Velocity Saturation Effect

TL;DR

This paper develops a comprehensive model for carrier conduction in wide bandgap semiconductors, revealing how velocity saturation influences the transition between contact-limited and space-charge-limited currents, especially at high voltages.

Contribution

It introduces a generalized transport model incorporating velocity saturation, contact injection, and space charge effects, clarifying high-voltage conduction mechanisms in wide bandgap semiconductors.

Findings

Velocity-saturated SCLC dominates high-voltage transport in GaN and SiC diodes.

The model unifies various conduction regimes including Fowler-Nordheim and trap-free SCLC.

Velocity saturation is identified as a key factor in high-field conduction in WBG materials.

Abstract

Carrier conduction in wide bandgap semiconductors (WBS) often exhibits velocity saturation at the high-electric field regime. How such effect influences the transition between contact-limited and space-charge-limited current in a two-terminal device remains largely unexplored thus far. Here, we develop a generalized carrier transport model that includes contact-limited field-induced carrier injection, space charge, carrier scattering and velocity saturation effect. The model reveals various transitional behaviors in the current-voltage characteristics, encompassing Fowler-Nordheim emission, trap-free Mott-Gurney (MG) SCLC and \emph{velocity-saturated SCLC}. Using GaN, 6H-SiC and 4H-SiC WBS as examples, we show that the velocity-saturated SCLC completely dominates the high-voltage ($10^2 \sim 10^4$ V) transport for typical sub-$\mu$m GaN and SiC diodes, thus unravelling velocity-saturated SCLC as a central transport mechanism in WBG electronics.