Investigation of a Novel Enhancement-Mode Al0.25Ga0.75N/AlN/Al X Ga(1-X)N/GaN MIS-HEMT for High Vth and Low R on,sp

In this article, we proposed a composite-barrier-metal–insulator–semiconductor-high electron mobility transistor (CB-MIS-HEMT), in which a thick Al_xGa $_{({1}-{x}{)}}\text{N}$ with small Al mol fraction is implemented in the gate region to achieve both high threshold voltage ( ${V}_{\text {th}}{)}$ and high electron mobility. A Al $_{{0}.{25}}$ Ga $_{{0}.{75}}\text{N}$ /AlN, working as a second barrier, is set on the Al_xGa $_{({1}-{x}{)}}\text{N}$ -layer to maintain high 2DEG density in the access region. The thick Al_xGa $_{({1}-{x}{)}}\text{N}$ in the gate region reduces the mobility degradation effects caused by the interface charges, acoustic phonon scattering, and surface roughness scattering. Combined with small Almol fraction design, both low specific ON-resistance (R_on,sp)and high ${V}_{\text {th}}$ can be obtained simultaneously. An analytical model for the electron density in both the lower and upper channels as well as ${V}_{\text {th}}$ is presented, which matches very well with the experimentally calibrated TCAD simulation. For a 600-V design, it shows that the electron mobility in the lower channel can be improved to 1255 cm²/ $\text{V}\cdot \text{s}$ , and at ${V}_{\text {th}}$ around 2.5 V, R_on,sp of the CB-MIS-HEMT can be reduced by 33.6% compared to a conventional recess-gate MIS-HEMT.