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NiO Equips Ga2O3 With Bipolar Conduction

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Diodes formed from p-type NiO and n-type β-Ga2O3 embrace the harsh transients found in power electronic systems BY JIANDONG YE, HAI LU AND RONG ZHANG FROM NANJING UNIVERSITY

βTHERE'S NO DOUBT that power electronic circuits are playing an ever-increasing role in our lives. They are key building blocks in big-data centres, electric vehicles, cloud computing and the internet of things. We have a diverse network of power electronic equipment to thank for keeping us immersed in the pleasure of technology at all times. To provide this level of service, circuits must operate for a long time without failure and handle unavoidable high-voltage/current transients.

These transients - momentary spikes in voltage or current - tend to be accompanied with lightning, electrostatic discharge. When power circuits experience such a sudden change in the switching process caused by transients, this threatens to disrupt or damage power devices connected to signal or power lines (see Figure 1). Such transients can deteriorate power systems, because power electronic devices have to operate under critical conditions of high voltages and large currents. Consequently, there is tremendous desire to increase the robustness of power devices against transients, as this will ensure the availability of essential building blocks for power modules providing safe operation.


Figure 1. The NiO/β-Ga2O3 power rectifiers, with different bevel angles adjusted by a magnetron sputtering system. Inset: schematic cross-section of NiO/β-Ga2O3 heterojunction diodes and a Ni/β-Ga2O3 Schottky barrier diode. The transient energy shocks that degrade device performance stem from the lumped or parasitic elements in the power circuit.

One option for ushering in an era of high-reliability power circuits is to replace silicon devices with those made from wide-bandgap semiconductors, which are well-suited to delivering high-temperature, high-power operation. Amongst these wide bandgap semiconductors, β-Ga2O3 has many attributes: an ultra-wide bandgap, an ultra-high breakdown electric field, and a decent electron mobility. These virtues make this oxide a very competitive candidate for high-power applications. Furthermore, Ga2O3 is renowned for its high thermal stability, ensuring high-temperature operation; and for its short minority carrier lifetime, enabling fast switching with low power losses.