We have fabricated enhancement-mode n-channel GaN MOSFETs with overlap gate structure on a p-GaN using thick HfO2 as a gate insulator. The maximum transconductance of 23 mS/mm which is 4 times larger, to our knowledge, than the best-reported value of the normally-off GaN MOSFETs with SiO2 gate oxide has been obtained.

High output power AlGaN/GaN metal-insulator-semiconductor (MIS) hetero-junction field effect transistor (HFET) on Si substrate for millimeter-wave application has developed. High temperature chemical vapor deposition (HT-CVD) grown SiN as a gate insulator improves the breakdown characteristics which enables the operation at high drain voltage of 55 V. The device exhibits high drain current of 1.1 A/mm free from the current collapse and high RF gain of 10.4 dB. The amplifier module developed AlGaN/GaN MIS-HFET with the gate width of 5.4 mm exhibits an output power of 10.7 W and a linear gain of 4 dB at 26.5 GHz. The resultant high output power is very promising for long-distance communication at millimeter-wave in the future which would enable high speed and high density data transmission.