ZrO2/InAlN/GaN Metal--Oxide--Semiconductor Heterostructure Field-Effect Transistors with InAlN Barrier of Different Compositions

We report on InAlN/GaN heterostructure metal--oxide--semiconductor field-effect transistors (MOSHFETs) with an InAlN barrier layer of different compositions ($x_{\text{InN}} = 13$, 17, and 21%) and ZrO 2 gate-insulator/passivation. Static measurements yielded higher drain currents than those on unpassivated HFET counterparts and the currents increased with decreased $x_{\text{InN}}$. Post deposition annealing of the ZrO 2 insulator had less influence on the static performance but remarkable changes were observed on the capacitance--voltage characteristics. The capacitance hysteresis in both channel depletion and barrier accumulation regions was significantly suppressed after annealing. This indicates a reduction of the interfacial trap states and of fixed charge in the oxide. Pulsed current--voltage measurements confirmed this conclusion --- the gate lag of only ${\sim}80$% was evaluated for 200 ns pulse width, independently on the composition of the InAlN barrier layer. These results support an application of high permittivity ZrO 2 gate-insulator/passivation for the preparation of high-performance InAlN/GaN MOSHFETs.