Vertical GaN power devices: current status and future prospects (Conference Presentation)

Abstract

Vertical GaN power devices have become recognized as a strong candidate of high power devices because several reports having over 1kV breakdown voltage and low on-resistance have been published. However, these data still include some issues to be solved for practical applications. A merit of GaN is potential of high channel mobility which results in low on-resistance compared with SiC. Therefore, channel structure having high channel mobility is essential for vertical GaN devices. Most useful property of GaN for high channel mobility is that AlGaN/GaN heterostructure can be used. Panasonic Group developed high performance vertical GaN device with 1.7kV withstand voltage and 1mΩcm2 on resistance in 2016. The device had an AlGaN / GaN channel with a p-GaN gate of which channel mobility was 500-1000cm2/Vs. This performance is beyond the performance of SiC-MOSFET for the first time. Though AlGaN/GaN channel is ideal as high mobility channel, it, however, is difficult to fabricate the normally-off channel with high threshold voltage. If conventional MOS channel is possible, simple structure normally-off with high threshold voltage will be possible. In recent years, a high channel mobility exceeding 100 cm2/Vs of MOS channel has been reported by the two groups. Fuji Electric Group showed high mobility of 120 cm2/Vs in the inverted channel of the MOSFET in 2017. And UC Davis group reported 185 cm2/Vs with a GaN channel regrown on the trench sidewall in the trench gate MOSFET in 2017. These data make the expectation of the possibility of higher channel mobility of MOS structure by improving the interface state.