GaN diodes with uniform, robust avalanche

A multi-faceted endeavour, starting with material growth and extending all the way to circuit-level investigation, ensures uniform, robust avalanche in GaN vertical power diodes.

BY BHAWANI SHANKAR AND SRABANTI CHOWDHURY FROM STANFORD UNIVERSITY

In every power electronic system, it is the power devices that provide the building blocks. When these semiconducting devices, often diodes and transistors, are used in power electronic circuits, they are often placed in series with inductive loads, such as a motor or a discrete inductor.

In this configuration, when device switching occurs, there’s an interruption to current flow through the series inductor – and this generates a voltage transient, appearing across the device terminals (see Figure 1). If the voltage transient exceeds the breakdown voltage of the device, this poses a threat to damage the device.

To prevent failures from such overvoltage scenarios, device engineers tend to design power devices with extra headroom in the breakdown voltage. But there are penalties to pay: a higher on-resistance, leading to an increase in conduction losses; and a higher device manufacturing cost, stemming from a hike in semiconductor estate associated with the larger drift region volume needed to hold the higher voltage.

Combatting this concern are semiconductor devices with an avalanche capability, which have an inherent overvoltage protection. When such devices face overvoltage transients in a circuit, they undergo avalanche breakdown and generate micro-plasma or current filaments that bypasses the electrical stress and protect the device.

Fortunately, one of the most promising materials for the future of power electronics, GaN, possess avalanche capability. However, despite more than three decades of exploration of this wide bandgap semiconductor as a mainstream device material, reports of its avalanche breakdown are limited to devices that have been grown on native GaN substrates.