We present the first working AlN/GaN HEMT with a 3 nm AlN barrier layer that provides high polarization induced charge densities for the 2DEG. Without the need for impurity doping the mobility of the AlN/GaN heterostructure is drastically increased and is the basis of HEMT technology. Also enhanced by the lack of alloy disorder scattering at the interface, the AlN/GaN heterostructure appears to be the ideal candidate for high speed applications. As the AlN barrier is quite thin it is presupposed that a high leakage current will persist through the gate contact. High-K dielectrics offer a possible solution to reduced gate leakage and allow the transconductance and scaling of the device to be optimized.
Preliminary results on non-optimized AlN/GaN devices show decent current-voltage characteristics amongst other characterization measurements performed. A major issue arose with obtaining ohmic contact to high quality AlN/GaN heterostructures. Lower quality AlN barriers have large dislocation densities and are easy to form ohmic contacts on, however with higher crystalline quality AlN, conventional methods of forming ohmic contacts seem to be of little value. Conventional and unconventional ohmic contact experiments to high quality AlN have been performed and discussed.