Comparative Analysis of In0.15Ga0.85N and β-Ga2O3 Back Barriers in β-Ga2O3-Buffered AlGaN/GaN HEMT Structures for High-Speed RF Electronics

This paper presents a detailed comparative analysis of β-Ga2O3-buffered Al0.25Ga0.75N/GaN high electron mobility transistors (HEMTs) incorporating two distinct back barrier configurations: In0.15Ga0.85N and a unified β-Ga2O3 layer. The devices are evaluated under two gate metal work functions (ϕₘ = 4.3 and 5.6 eV) to examine their influence on device performance. DC and RF characteristics, including drain current (ID), transconductance (gₘ), and unity current gain cutoff frequency ( fT), are extracted at a drain bias of 20 V. The β-Ga2O3 back barrier device demonstrates superior performance, achieving higher peak drain current densities of 6 A/mm (ϕₘ = 4.3 eV) and 5.63 A/mm (ϕₘ = 5.6 eV), compared to 3.9 and 3.6 A/mm, respectively, for the InGaN counterpart. A significant shift in threshold voltage (Vth) is observed with the β‑Ga2O3 barrier, indicating enhanced channel control. Moreover, transconductance values exceeded 1 S/mm, and peak fT values approached 1.45 × 1011 Hz, underscoring the advantages of β-Ga2O3 in high‑speed applications. The ON-resistance (Ron) analysis shows that the β-Ga2O3 back barrier device achieved a minimum Ron of 0.28 Ω mm (ϕₘ = 4.3 eV), compared to 0.55 Ω mm for the InGaN back barrier. The results establish that both the gate work function and back barrier selection critically impact the electron confinement, threshold behavior, and high-frequency response of GaN-based HEMTs on β-Ga2O3 substrates.