Sequential Channel Activation in Multi-Channel AlGaN/AlN/GaN HEMTs: From 4-Channel to Double-Sided 5-Channel Configurations

This study investigates the critical impact of channel scaling on the performance of AlGaN/AlN/GaN high-electron-mobility transistors (HEMTs) by comparing a 4-channel stack structure and a 5-channel double-sided channel structure. While multi-channel designs are intended to enhance current density, the results reveal a complex trade-off between carrier volume and gate electrostatic control. The 4-channel HEMT, with a periodic AlGaN/AlN/GaN stack, achieved the drain current (IDS) of 1.35 × 10–2 A and a peak transconductance (gm) of 2.2 × 10–3 S at VGS = 0 V. In contrast, the 5-channel HEMT, with a novel 2-pair double-sided GaN/AlN/AlGaN/AlN/GaN configuration, exhibited a slightly lower IDS of 1.05 × 10–2 A and a gm value of 1.4 × 10–3 S, attributed to increased series resistance and inter-channel scattering in the deeper layers. A significant highlight of this work is the observation of sequential channel activation: the transfer characteristics exhibit exactly four and five distinct gm peaks for the HEMT devices, providing direct evidence of independent channel modulation and pinch-off. Despite the increased complexity, both structures maintained high crystalline quality, as confirmed by X-ray satellite peaks and sharp heterostructure interfaces observed in TEM micrographs. These multiple-channel AlGaN-based HEMT structures with an AlGaN/AlN/GaN stack and a double-sided channel were fabricated for high-current-density, short-channel-width AlGaN-based HEMT device applications.