Impact of Lateral Scaling on the High-Frequency Performance of β-Ga2O3 Back-Barrier GaN HEMTs with a Graded InAlN Buffer

This work investigates the impact of lateral scaling on the high-frequency characteristics of a β-Ga2O3 back-barrier (BB) HEMT incorporating a compositionally graded InAlN buffer. The proposed device structure consists of a sapphire substrate, graded InAlN buffer, β-Ga2O3 BB, GaN channel, and AlGaN barrier layer. The influence of LG and LGS on carrier confinement, electrical performance, and RF characteristics is systematically analysed. Energy band analysis reveals the formation of a deep quantum well at the heterointerface, facilitating strong 2DEG. The β-Ga2O3 BB effectively suppresses electron leakage toward the buffer region, while the graded InAlN buffer improves carrier transport through reduced scattering. The device exhibits a maximum drain current of approximately 2.4 A/mm at V_GS = 2 V for LG = 20 nm and a peak transconductance of about 1.55 S/mm. High-frequency analysis demonstrates a maximum fT of nearly 300 GHz for optimized LGS and 250 GHz for LG = 20 nm. Furthermore, reduced gate length significantly lowers parasitic capacitances, leading to enhanced RF performance. The results indicate that lateral scaling strongly influences carrier transport, electrostatic control, and frequency response, with gate-length scaling exhibiting a more pronounced effect than source-to-gate spacing variation. The proposed β-Ga2O3 back-barrier architecture with a graded InAlN buffer demonstrates considerable potential for microwave, millimeter-wave, and advanced RF applications.