Formation of ohmic contacts to ultra-thin channel AIN/GaN HEMTs

AIN/GaN-based high electron mobility transistors with ultra-thin AlN barriers of 2.3 - 5 nm are attractive candidates for very high speed applications owing to the aggressive scalability such structures afford. We report the first study on formation of ohmic contacts to, these high quality ultra-thin channel heterostructures (n(s) > 1 x 10(13) cm(-2) and mu > 900 cm(2)/Vs) with systematically varying, barrier thicknesses. While the conventional ohmic contacts to AlGaN/GaN structures generally require high temperature annealing, these ohmic contacts were found to behave ohmic or near ohmic as-deposited. Annealing, (400-860 degrees C) improves the contact resistance to a range of 0.8 - 2 ohm-mm but the annealing conditions strongly depend on,ithe AlN thickness as well as the heterostructure quality (mu). All alloyed contacts show smooth morphology, making them suitable for e-beam lithographically defined gate, patterning.