High Electron Mobility Transistors With Al0.65Ga0.35N Channel Layers on Thick AlN/Sapphire Templates

We report Al 0.85 Ga 0.15 N/Al 0.65 Ga 0.35 N high-electron mobility transistors on low-defect AlN buffer layers over basal plane sapphire substrates. A new epilayer design consisting of a doped barrier layer yielded sheet resistivity values as low as 1800 Ω/□. Devices with the source-drain spacing of 5.5 μm and a gate length of 1.8 μm exhibited peak drain-currents as high as 250 mA/mm at a gate bias of +4 V. We also show that the 3-μm thick low-defect AlN buffer layers over sapphire to provide sufficient thermal conduction which enables stable device operation up to at least 40 V at 250 mA/mm with no current droop.