Al0.65Ga0.35N channel high electron mobility transistors on AlN/ sapphire templates

We report on an Al
_{0 85}
Ga
_0.15
N-Al
_{0 65}
Ga
_{0 35}
N high electron mobility transistor (HEMT) on low-defect AlN buffers over basal plane sapphire substrates. A new epilayer design consisting of a doped barrier layer yielded sheet resistivity values as low as 1800 Ω per square. Devices with a source-drain spacing of 5.5 μm and a gate length of 1.8 μm exhibited peak drain-currents as high as 290 mA/mm at a gate bias of +4 volts. This is at least an order of magnitude higher than previous reports. We also show that 3 μm thick low-defect AlN buffer layers provide enough thermal conduction enabling stable device operation over 250°C.