AlN/AlGaN heterostructure field-effect transistor power devices advantageous for high-temperature application

We report a high-quality AlN/Al0.73Ga0.27N heterostructure field-effect transistor (HFET) advantageous for high-temperature application. The epitaxial heterostructures exhibit a full width at half maximum of 79 arc sec in the (0002) XRD rocking curve, a surface roughness of 0.35 nm, a room-temperature two-dimensional electron gas density of 1.4 × 1013 cm−2 and mobility of 147 cm2/V/s. Two-terminal mesa breakdown measurements revealed an intrinsic critical electric field of 5.6 MV/cm for a 3 μm gap. AlN/Al0.73Ga0.27N HFET devices with gate–drain spacings of 5, 10, 25, and 50 μm were fabricated, and the breakdown voltages are 990, 1420, 2045, and 4203 V, respectively. Remarkably, the saturated drain current exhibits a positive temperature coefficient, in contrast to the negative coefficient in conventional gallium nitride high-electron-mobility transistors, and the threshold voltage decreases from −9.3 to −7.9 V in the temperature range from 25 to 175 °C. This anomalous behavior is attributed to dominant carrier de-trapping from deep-level traps, confirmed by pulsed I–V measurements, temperature-dependent C–V, and Hall measurements. These observations provide strong evidence for the multi-kilovolt-class and high-temperature power switching applications of the AlN/Al0.73Ga0.27N HFET devices.