200mm single crystal for vertical GaN transistors

Toyoda Gosei in Japan has developed a 200mm single crystal wafer of gallium nitride (GaN) for vertical transistors.

Building vertical transistors provides higher density power devices over using lateral transistors with a GaN-on-silicon process which can be used on 200mm and 300mm wafers. However previous single crystal wafers have struggled to create single crystals larger than 4in.

Researchers at Osaka University and Toyoda Gosei fabricated a 200mm multi-point seed (MPS) substrate and succeeded in growing hexagonal GaN crystals with a diagonal length of just under 200mm on the substrate. This used an Na-flux process which is a well-established high temperature liquid phase epitaxy (LPE) process. The researchers expect the Na-flux method to be a key technique for obtaining ideal bulk GaN crystals.

The substrate was used to grow 600V vertical GaN transistors with normally off operation with a gate voltage threshold exceeding 2 V and a maximum drain current of 3.3 A during the on-state operation. Additionally, it demonstrates a breakdown voltage exceeding 600 V and a low leakage current during off-state operation.

The Japanese Ministry of the Environment is leading a project for broad application of GaN power devices, and Toyoda Gosei is providing the underlying wafers to obtain ideal GaN crystals.

One outcome of the project is a demonstrable improvement in power device performance with a GaN substrate fabricated on the GaN seed crystal that Toyoda Gosei jointly developed with Osaka University. Compared to power devices made on commercially-available substrates, power devices using these GaN substrates show higher performance in both power regulation capacity and yield ratio.

The company has previously developed a high voltage 1500V lateral GaN transistor for a 24kW solar farm power converter.

Toyoda Gosei will continue collaborating with government, universities, and other corporations to provide the single crystal GaN substrates.