Investigation of AlN back barrier/GaN HEMTs with ultra-thin GaN channel for high-frequency and high-voltage applications

AlN back-barrier thickness physically governs ultrathin-channel GaN high-electron-mobility transistor (HEMT) performance by dictating a competition between material states. At 440 nm, the AlN back barrier effectively relaxes strain while maintaining two-dimensional growth, yielding high mobility and a trap profile favorable for robust short-channel breakdown and high-frequency operation—resulting in fT/fmax = 34.32/70.95 GHz and 69% power-added efficiency at 3.6 GHz. For a thicker 1-μm layer, three-dimensional island growth with deep-level traps dominates, providing superior vertical blocking to achieve 1.78 kV breakdown voltage for high-voltage operation. By linking the AlN back-barrier thickness to these underlying physical mechanisms, this work establishes a physics-based design framework for deterministically tailoring GaN HEMTs toward high-frequency or high-voltage operation, thereby opening a viable pathway to advance the performance limits of nitride electronics.