Ti/Al/Mo/Au Ohmic contacts to all-binary AlN/GaN high electron mobility transistors

Electrical and microstructural characterizations of the Ti/Al/Mo/Au Ohmic contacts to ultrathin AlN/GaN heterostructures were carried out. It was found that as-deposited contacts had linear I-V behavior due to high tunneling current across the thin AlN barrier. A contact resistance of 0.455 Omega mm was obtained for samples annealed at 800 degrees C without any premetallization plasma treatment. Transmission electron microscopy studies showed that despite the use of Ti, the AlN layer remained intact. Mushroom-shaped TiN protrusions were formed only along threading dislocations, which terminated in the AlN layer. The TiN protrusions acted as metal plugs/spikes thereby aiding carrier transport.