Investigation of microwave and noise properties of InAlN/GaN HFETs after electrical stress: role of surface effects

ABSTRACT In an effort to investigate the particulars of their stability, In 18.5% Al 81.5% N/GaN HFETs were subjected to on-state electrical stress for intervals totaling up to 20 hours. The current gain cutoff frequency f T showed a constant increase after each incremental stress, which was consistent with the decreased gate lag and the decreased phase noise. Extraction of small-signal circuit parameters demonstrated that the increase of f T is due to a decrease in the gate-source capacitance (C gs ) and gate-drain capacitance ( C gd ) as well as the increased microwave transconductance ( g m ). All these behaviors are consistent with the diminishing of the gate extension (“virtual gate”) around the gate area. INTRODUCTION In x Al 1-x N/GaN based heterojunction field effect transistors (HFETs) are candidates for next generation high-power and high-frequency amplifiers 1 , owing to a large two-dimensional electron gas (2DEG) in the heterostructure due to the large spontaneous polarization charge at the InAlN/GaN interface. Moreover, at the same time the InAlN layer can be grown lattice-matched to the underlying GaN layer for an indium composition between 17% to 18%