Investigation of interfaces and threshold voltage instabilities in normally-off MOS-gated InGaN/AlGaN/GaN HEMTs

[Display omitted] •Normally-off devices prepared by polarization engineering using InGaN layer.•Polarization charge at the InGaN/AlGaN interface confirmed by XPS.•Peculiar threshold voltage shift during positive gate bias stress experiment.•Holes from 2DHG recombine with electrons in InGaN layer generating photons. Polarization engineering is a promising approach to achieve high positive threshold voltage (Vth) in GaN-based metal-oxide-semiconductor high electron mobility transistors (MOS HEMTs). In this paper, we investigate all critical interfaces of polarization-engineered normally-off Al2O3/InGaN/AlGaN/GaN MOS HEMTs using transmission electron microscopy and X-ray photoelectron spectroscopy. Mechanisms of threshold voltage (VTH) instabilities are also analyzed. Devices were subjected to positive-bias stress-recovery experiments to capture the transient change in Vth. We propose a model that explains observed peculiar behavior and discuss the role of 2-dimensional hole gas (2DHG) in Al2O3/InGaN/AlGaN/GaN MOS HEMTs Vth shift.