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

We report on an Al0.85Ga0.15N-Al0.65Ga0.35N 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 Omega per square. Devices with a source-drain spacing of 5.5 mu m and a gate length of 1.8 mu m 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 mu m thick low-defect AN buffer layers provide enough thermal conduction enabling stable device operation over 250 degrees C.