Improvement of DC and f _T performances of graded-channel HEMTs by polarization engineering

Abstract

The graded-channel high-electron-mobility transistors (HEMTs) with graded AlGaN buffer are investigated in this paper by Atlas drift-diffusion simulation. The short-channel effects (SCEs) are suppressed in a manner by employing the graded AlGaN buffer instead of the fixed Al-content AlGaN buffer. Then, the Al-content of the graded AlGaN channel is also optimized. The flatter and wider transconductance and current gain cutoff frequency (fT) curves are garnered by utilizing the graded AlGaN channel whose top Al-content is the same as the AlGaN barrier. At the gate length (LG) of 50 nm, the saturated drain current of the proposed device is 0.98 A/mm, which is 34% higher than the reference device. Simultaneously, the fT and fT×LG are also analyzed with the gate length from 50 nm to 250 nm. The fT of the proposed architecture is 181 GHz at LG = 50 nm and VGS = 1 V which is 12% higher than the reference device under the same conditions. The fT×LG is up to 19.2 GHz·μm at the gate length of 250 nm, and it obtains a 12% improvement over the reference device.