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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{7}}$ </tex-math></inline-formula> cm/s in high-composition Al<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{0.64}}\text {Ga}_{{0.36}}$ </tex-math></inline-formula>N channel high-electron-mobility transistors (HEMTs) at peak <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{t}$ </tex-math></inline-formula>. The small-signal two-port s-parameter measurements were employed at peak <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{t}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{t}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.15\times 10^{{7}}$ </tex-math></inline-formula> cm/s. These findings offer crucial insights for optimizing the design and performance of high-composition AlGaN channel HEMTs at RF power frequencies.