Origin of threshold voltage instability in vertical GaN trench MOSFETs characterized by charge pumping

Abstract

We systematically investigate threshold voltage (Vth) instability in vertical GaN trench MOSFETs on sapphire using a charge pumping (CP) method combined with pulsed gate measurements. A negative Vth shift and reduced hysteresis are observed when switching the gate bias from DC to pulsed mode with a negative quiescent gate bias; this behavior is attributed directly to oxide trapping in the gate stack. Using the CP technique, we quantitatively extract the trap density, energy levels, and depth profiles of both border oxide traps and interface states in the Al2O3/p-GaN sidewall gate stack. An integrated border trap density of 7.28 × 1012 cm−2 is deduced, and amorphous Ga–O–Al bonds formed during atomic layer deposition are identified as the potential physical origin of the Vth shift and hysteresis (ΔVth). Our analysis demonstrates that the CP approach goes beyond offering valuable insights into interface properties; it provides a powerful, quantitative diagnostic tool to directly guide the optimization of gate dielectrics in next-generation reliable vertical GaN trench MOSFETs for power applications.