Fabrication of normally-off mode GaN and AlGaN/GaN MOSFETs with HfO2 gate insulator

We have fabricated III-nitride metal-oxide field effect transistors (MOSFETs) using high-k HfO2 as a gate oxide. Two types of MOSFETs were studied; GaN MOSFETs and AlGaN/GaN MOSFETs. In the case of GaN MOSFETs, the maximum transconductance of 45 mS/mm has been obtained. This is seven times larger than the best-reported value, to our knowledge, for the normally-off GaN MOSFETs with SiO2 gate oxide. In order to improve the performance of the device, AlGaN/GaN MOSFETs in which high-quality AlGaN/GaN heterointerface is used as a channel have been fabricated. The maximum transconductance and drain current were as high as 160 mS/mm and 840 mA/mm, respectively.