Step-graded AlGaN barrier engineering in AlGaN/GaN HEMTs for high-linearity low-noise RF amplifiers

Compositionally graded AlGaN barrier GaN-HEMTs present a promising path to enhance device linearity, which is essential for low-noise radio-frequency (RF) amplifiers. In this work, a step-graded (SG) AlGaN/GaN HEMT is proposed and systematically investigated to explore the advantage of graded barrier compared to conventional HEMTs. The effect of Al-composition on DC/RF performance of the conventional HEMT (CHEMT), is initially analyzed, where 25% Al composition delivered optimal performance. Further, a step-graded (SG) barrier (Al composition varying from 25% to 15%) is introduced, forming an SGHEMT. The outcomes show that, graded barrier allows for a modified 2DEG confinement resulting in more distributed carrier profile, offering improved and broader transconductance (g_m), and suppressed higher-order nonlinearities, thereby enhancing device linearity. Additionally, the impact of drain bias is also studied, where the SGHEMT achieves maximum performance at V_DS = 5 V, due to enhanced electric field and improved carrier transport. Moreover, thickness of SG-AlGaN barrier is scaled from 22 nm to 11 nm to achieve better electrical performance. The optimized SGHEMT with 11 nm barrier is found to have g_m of 420.4 mS/mm, maximum I_D of 1.83 A/mm, higher I_d-sat of 2.82 A/mm, & enhanced f_T of 154.3 GHz due to better channel electrostatics, enhanced carrier confinement, improved drive current capability. paving the way for better linearity performances. These results emphasize exceptional DC/RF performance traits of proposed SGHEMT, rendering it a strong candidate for low-noise RF amplifiers that demand high linearity operation.