Normally-off operation AlGaN/GaN high electron mobility transistors have been developed utilising a fluorine-based treatment technique combined with a metal-oxide-semiconductor gate architecture. Threshold voltage as high as 5.1 V was achieved by using an 16 nm-thick Al 2 O 3 gate oxide film. Additionally, the device performed a drain current density of 500 mA/mm and a peak transconductance of 100 mS/mm, which are comparable to the conventional normally-on devices.Introduction: AlGAN/GaN-based high electron mobility transistors are promising candidates for power electronic applications owing to their attractive properties, such as high breakdown field, high electron mobility, and capability of high temperature operation. For power switching applications, devices with normally-off operation are necessary because they can not only help simplify the complexity of the circuit but also reduce standby power consumption. In addition, they provide a fail-safe function because a noise higher than 3 V may occur on the gate electrode during the device operation [1]. Several approaches towards such requirements based on an AlGaN/GaN heterostructure have been investigated, such as the recessed gate [2], fluoride-based treatment [3], and the band diagram engineered approach [4,5]. However, these approaches still encounter an issue which is either lower current density or insufficient threshold voltage for the gate noise blocking. In this Letter, we combined the fluorine-based treatment technique and an Al 2 O 3 film as the gate oxide layer to demonstrate normally-off operation AlGaN/GaN MOS-HEMTs with high threshold voltage, and with comparable current density to conventional normally-on HEMTs
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