Ultrathin AlN∕GaN heterostructure field-effect transistors with deposition of Si atoms on AlN barrier surface

We deposited Si atoms on the AlN barrier surface of an ultrathin AlN∕GaN heterostructure field-effect transistor (HFET). This induced a remarkable change in the electrical properties of the two-dimensional electron gas. A 2-nm-thick Si layer reduced the sheet resistance of an AlN∕GaN HFET (AlN barrier, 2nm) from 60356to388Ω∕sq. The effect on the Ohmic contact was also significant: the presence of an undermost layer of Si atoms under Ohmic contacts produced a low specific contact resistance of 1.7×10–6Ωcm2. A 50-nm-gate AlN∕GaN HFET with a Si layer exhibited excellent device characteristics with a current-gain cutoff frequency of 106GHz.