Inelastic-stress-induced threshold instability and mobility degradation in AlN/GaN MIS-HEMTs on Si

Abstract

This work investigates the impact of stress-induced effects on the stability of AlN/GaN MIS-HEMTs on Si employing PECVD-SiN as a passivation layer. DC and temperature-dependent C–V/I–V measurements together with technology computer-aided design simulations are used to correlate stress state, defect behavior, and channel transport. As-deposited PECVD-SiN introduces strong inelastic stress that compresses the 2DEG near the GaN surface and drives an anomalous reverse shift of the threshold voltage of ∼−0.3 V between 300 and 475 K, with room-temperature mobility limited to ∼700 cm2 V−1 s−1 by remote scattering. Arrhenius analysis of the drain current yields an activation energy Ea = 0.059 eV, attributed to thermally activated charging and restructuring of bulk and interface defects coupled to the stress field. Post-passivation annealing at 450 °C largely relaxes the inelastic component, broadens the potential well, and reduces Ea to 0.019 eV. The mobility increases to ∼1260 cm2 V−1 s−1 and exhibits a polar optical phonon-like temperature dependence, while the VTH–T behavior changes to a weak positive coefficient. These results offer insights on the temperature stability of stress-induced GaN MIS-HEMTs from a material perspective.