This work demonstrates the profound impact of back-barrier composition on the performance of GaN high-electron-mobility transistors (HEMTs) on a β-Ga2O3 substrates. Through a comparative study of two device architectures, we reveal a fundamental design trade-off between high-frequency gain and breakdown robustness. The first employs a conventional compositionally-graded AlGaN back barrier, while the second introduces a novel compositionally-graded InGaN back barrier. Extensive characterization shows that the larger conduction band offset provided by the InGaN layers in the suggested structure enables superior vertical carrier confinement. This results in a 15.5% higher maximum drain current (5.58 vs. 4.83 A/mm), an 11% higher peak transconductance (2.12 vs. 1.91 mS/mm), a 13% lower on-resistance (0.27 vs. 0.31 Ω mm) and a significantly reduced gate-drain capacitance (250 vs. 380 fF/mm). The device with the graded-InGaN back barrier achieves a markedly higher cutoff frequency of 199 GHz, compared to 169 GHz for the conventional architecture. These results provide critical design guidelines, positioning the graded-InGaN back barrier as the premier choice for high-gain RF amplification and the graded-AlGaN barrier for high-voltage power application.
Jiavana et al. (Thu,) studied this question.