Investigation on impact of AlxGa1-xN and InGaN back barriers and source-drain spacing on the DC/RF performance of Fe-doped recessed T-gated AlN/GaN HEMT on SiC wafer for future RF power applications

Abstract

The work function (φm) of gate metal is crucial to electrical characteristics in standard GaN-based high electron mobility transistors (HEMTs). In this simulation report, RF & DC performance of recessed T-gated Fe-doped AlN/GaN HEMT device with AlxGa1-xN back barrier (BB) and InGaN BB is explored by varying gate metal work functions which is a flexible approach to obtain wide modulation range of threshold voltage (Vth) with a positive shift. The simulations are carried out at an applied drain voltage of 1.4 V. As Al-content of AlxGa1-xN BB layer has an impact on surface roughness with GaN channel and effective mobility of electrons in the two-dimensional electron gas (2DEG), this work includes tuning the aluminum mole fraction. In comparison, the proposed device with Al0.15Ga0.85N BB layer exhibits high GM of 381.4 mS/mm with φm = 5.25 eV, highest ID of 0.702 A/mm with φm = 4.5 eV, and high fT/fmax of 173.1/247.4 GHz with φm = 5.25 eV which can be ascribed to enhanced mobility and carrier confinement in the quantum well due to integration of BB, presence of Fe-doping in the buffer in conjunction with recessed T-gate approach. Hence, optimized performance is achieved with Al0.15Ga0.85N BB layer at φm = 4.5 eV. In addition, we investigated the effect of scaling gate-to-source spacing (LGS) with constant gate-to-drain spacing (LGD) and vice-versa, on the device performance. The device with Al0.15Ga0.85N BB exhibited supreme performance at LGS = 300 nm with LGD = 800 nm, due to enhanced electric field component along the channel as a result of downscaling lateral device dimensions. No wonder, this device can be considered as most promising for future military, defence, and RF power applications.