Demonstration of Effective Intrinsic Electron Velocity >107 cm/s in Ultrawide Bandgap Al₀.₆₄Ga₀.₃₆N Channel HEMTs

This article reports on the effective intrinsic electron velocity exceeding $10^{{7}}$ cm/s in high-composition Al $_{{0.64}}\text {Ga}_{{0.36}}$ N channel high-electron-mobility transistors (HEMTs) at peak ${f}_{t}$ . The small-signal two-port s-parameter measurements were employed at peak ${f}_{t}$ bias, which enabled us to compute the small-signal parameters and determine the total transit delay. A device with ~245-nm gate length yielded a total transit delay of 8.04 ps corresponding to a peak ${f}_{t}$ of 19.8 GHz. By segregating the delay components, the intrinsic delay was estimated to be 6.22 ps. However, this intrinsic delay includes the effect of fringe capacitances that were further decoupled to yield the intrinsic transit time. The transit time under the gate was estimated to be 2.12 ps, and thus, the peak effective intrinsic electron velocity was determined to be $1.15\times 10^{{7}}$ cm/s. These findings offer crucial insights for optimizing the design and performance of high-composition AlGaN channel HEMTs at RF power frequencies.