Inversion-channel GaN MOSFET using atomic-layer-deposited Al2O3 as gate dielectric

For the first time, inversion-channel GaN MOSFETs using atomic-layer-deposited (ALD) Al<inf>2</inf>O<inf>3</inf> as a gate dielectric have been successfully fabricated, showing well-behaved drain I–V and transfer characteristics. The drain current was scaled with gate length, showing a maximum drain current of 10 mA/mm in a device of 1 µm gate length, at a gate voltage (V<inf>gs</inf>) of 8 V and a drain voltage (V<inf>ds</inf>) of 10V. High I<inf>on</inf>/I<inf>off</inf> ratio of 2.5×10⁵ was achieved with a very low off-state leakage of 4×10⁻¹³A/µm. In addition, depletion-mode (D-mode) GaN MOSFETs have also been demonstrated, showing a very low on-resistance of 2.5 mΩ⋅cm², a high mobility of 350 cm²/Vs, and a high maximum drain current of 300 mA/mm in a device of 4 µm gate length.