High Performance in a Normally-off Al2O3/GaN MOSFET Based on an AlGaN/GaN Heterostructure with a p-GaN Buffer Layer

An AlGaN/GaN-based normally-off GaN metal-oxide-semiconductor field-effect transistor (MOSFET) with a p-GaN buffer layer and using an over-recessed gate structure has been demonstrated for the first time. The p-GaN buffer layer is believed to have advantages of not only ensuring a fairly positive threshold voltage due to the depletion effect but also reducing the buffer leakage current. The over-recessed gate region and the whole surface of the AlGaN layer were covered with a high-quality atomic layer-deposited (ALD) Al2O3 layer, which play a role as an excellent gate insulator in the recessed gate region and a surface passivation layer in the ungated region between the source and the drain. The fabricated GaN MOSFET with 30-nm-thick ALD Al2O3 exhibited good device performances, such as a maximum drain current of 109 mA/mm, a maximum extrinsic transconductance of 30 mS/mm, a low specific on-resistance of 1.86 m Omega.cm(2), and a subthreshold slope of 365 mV/dec with a threshold voltage of 2.6 V.