Recessed-gate AlGaN/GaN enhancement-mode (E-mode) heterostructure field-effect transistors (HFETs) with enhanced-barrier structures were fabricated, and their high-temperature characteristics were examined. Owing to enhanced-barrier structures, where a thin AlGaN layer with a higher Al composition is inserted into the AlGaN barrier, excellent E-mode operation with threshold voltage (Vth) higher than +3 V and drain current density (Id) higher than 600mA/mm was obtained at room temperature. Interestingly, Id did not decrease much at high temperatures, i.e., Id decreased from 610 to 590mA upon a temperature raise from RT to 300 °C. Open-gate devices with and without recessed-gate structures were fabricated and their two-terminal characteristics were comparatively examined, revealing that the observed peculiar characteristics are ascribed to recessed-gate structures. A model for explaining the observed high-temperature characteristics is proposed.
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