Simulation investigation of double-heterostructure T-gate HEMT with graded back-barrier engineering for improved RF performance

Abstract

This article proposes a 70 nm T-gate In0.17Al0.83N/AlN HEMT. The RF and DC characteristics of the proposed structure are investigated using the Silvaco Atlas tool. The proposed device has the graded back-barrier feature, which improves the carrier confinement at the GaN/AlGaN junction by increasing the conduction band discontinuity. The reduction of Al composition in the back-barrier layer led to the lattice’s complete relaxation. The presence of a graded back-barrier diminished the piezoelectric polarization, which significantly reduced the 2DEG concentration of the parasitic channel (1.0 × 1018 cm3) about two times and enhanced the transfer characteristics compared to the Al0.1Ga0.9N back-barrier. Moreover, the surface of the device is also passivated with the SiN layer, source/drain regions are highly doped, and the shape of the gate is taken as a T shape. These features improve the transconductance (740 mS/mm), drain current density (2.5 A/mm), cut-off frequency (295 GHz), and maximum oscillation frequency (323 GHz).