Optimized DC and RF Characteristics of ScAlN/InGaN/GaN HEMTs on Silicon Carbide using Step-graded AlGaN Buffer Layers

The incorporation of scandium aluminum nitride (ScAlN) in high-electron-mobility transistors (HEMTs) offers promising advances for next-generation electronics. Our research explores a novel device architecture featuring ScAlN/InGaN/GaN heterostructures with compositionally graded AlGaN buffer layers on SiC substrates. We conducted detailed numerical simulations with physics-based models to analyze the performance characteristics of a 55 nm-gate Sc0.2Al0.8N/In0.1Ga0.9N/GaN HEMT incorporating a stepped AlGaN buffer where aluminum content increases progressively from 0.1 to 0.7. This engineered buffer configuration enhances electron confinement and optimizes electric field distribution throughout the device. Performance metrics reveal impressive capabilities, including 4.0 A/mm maximum drain current, 0.75 S/mm peak transconductance, and 4.92 V gate voltage swing. The transistor shows excellent linearity with 55.6 V OFF-state breakdown voltage while delivering superior RF performance with 285 GHz cutoff frequency (fT) and 293 GHz maximum oscillation frequency (fmax). Our proposed HEMT design shows a Johnson Figure of Merit of 4.97 THz·V for the ScAlN-based HEMT with graded AlGaN buffer layers. This performance metric indicates the device capability to operate effectively in millimeter-wave frequency applications requiring both high power and high frequency operation.