Role of gate leakage suppression in revealing thermally induced barrier lowering in AlGaN/GaN HEMTs

In this work, we investigate how thermally excited surface states influence OFF-state transport and barrier modulation in AlGaN/GaN MSHEMTs by comparing NbN-gated and conventional Ni/Au-gated devices over a wide temperature range. Increasing temperature activates donor-like surface states, generating additional positive surface charge that raises the channel potential Va and enhances leakage through the GaN buffer. Whether this intrinsic electrostatic modulation becomes electrically visible depends critically on the magnitude of gate leakage. NbNgated MSHEMTs exhibit strongly suppressed gate leakage, allowing the temperature-induced increase in Va to manifest as a clear onset and leftward shift of OFF-state and subthreshold characteristics, along with systematic shifts in threshold voltage. In contrast, Ni/Au-gated MSHEMTs remain leakage-dominated in the OFF and subthreshold regimes, where gate-and leakage-assisted transport masks the electrostatic signature of surface-charge-induced barrier modulation, despite its intrinsic presence. The observed temperature evolution of OFF-state metrics is therefore governed by the competition between electrostatic control and leakage-assisted transport, establishing gateleakage suppression as essential for electrically resolving thermally induced barrier modulation in AlGaN/GaN heterostructure transistors.