Quaternary Barrier InAlGaN HEMTs With $f_{T}/f_{\max}$ of 230/300 GHz

Abstract

Depletion-mode quaternary barrier <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{In}_{0.13}\hbox{Al}_{0.83}\break \hbox{Ga}_{0.04}\hbox{N}$</tex></formula> high-electron-mobility transistors (HEMTs) with regrown ohmic contacts and T-gates on a SiC substrate have been fabricated. Devices with 40-nm-long footprints show a maximum output current density of 1.8 A/mm, an extrinsic dc transconductance of 770 mS/mm, and cutoff frequencies <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f_{T}/f_{\max}$</tex></formula> of 230/300 GHz at the same bias, which give a record-high value of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\surd f_{T} \cdot f_{\max} = \hbox{263}\ \hbox{GHz}$</tex> </formula> among all reported InAl(Ga)N barrier HEMTs. The device speed shows good scalability with gate length despite the onset of short-channel effects due to the lack of a back barrier. An effective electron velocity of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{1.36} \times \hbox{10}^{7}\ \hbox{cm/s}$</tex></formula> , which is comparable with that in the state-of-the-art deeply scaled AlN/GaN HEMTs, has been extracted from the gate-length dependence of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f_{T}$</tex></formula> for gate lengths from 100 to 40 nm.