Ta2O5-based recessed-gate enhancement-mode GaN HEMT with exceptionally low gate leakage and high ION/IOFF ratio: Determination of performance window for recessed-gate architecture

Enhancement-mode AlGaN/GaN high electron mobility transistors (HEMTs) are indispensable for fail-safe operation in power electronics. This work demonstrates enhancement-mode AlGaN/GaN metal–oxide–semiconductor HEMTs with partially and completely recessed gates. A low-damage digital recess etching process was employed, and thermally grown Ta2O5 was utilized as the gate dielectric. The effectiveness of Ta2O5 as a high-quality gate insulator was confirmed through key electrical parameters, including subthreshold swing, ION/IOFF ratio, and gate leakage current. The threshold voltages of the partially and completely recessed devices were 0.2 and 4.7 V, respectively. All devices exhibited an ION/IOFF ratio of approximately 1010, with corresponding subthreshold slopes of 63.6, 66.8, and 120.3 mV/dec. The gate leakage current remained extremely low, demonstrating the excellent dielectric integrity and interface quality. The respective saturation drain currents were 185, 182, and 83 mA/mm at a gate-to-source overdrive voltage of 1 V. A higher recess depth leads to degradation of the drive current and the on-resistance of the transistor at the cost of increasing the threshold voltage. The comparative analysis of no-recess, partially recessed, and fully recessed gate architectures establishes the performance boundaries and design trade-offs of recessed-gate AlGaN/GaN HEMTs.