Phonon-Assisted Charge Trapping and Threshold Voltage Modulation in MoS₂ FETs with AlO_xN_y Overlayers

In this study, we demonstrate that a room-temperature reactively sputtered aluminum oxynitride (AlO_xN_y) overlayer enables both effective doping and pronounced threshold voltage hysteresis in multilayer MoS₂ FETs, while preserving field-effect mobility. Compared to conventional AlO_x, the AlO_xN_y layer introduces trap states that are energetically aligned with the conduction band of MoS₂, facilitating charge exchange across the heterointerface. Capacitance-voltage measurements confirm that nitrogen incorporation reduces the effective fixed charge density, enabling mobility-preserving operation without thermal annealing. Notably, the hysteresis window exhibits a marked expansion above ∼250 K, which correlates with the activation of out-of-plane phonon modes in MoS₂. These phonons are proposed to assist in activating interfacial trap states within the AlO_xN_y layer, as supported by temperature-dependent electrical and spectroscopic analyses. While such trap-induced hysteresis may be undesirable for logic circuits, it offers valuable functionality for emerging device architectures─such as in-memory computing and neuromorphic systems─where hysteresis can be exploited. These findings underscore the potential of AlO_xN_y as a low-temperature-processable dielectric for 2D FETs and advance a new perspective on phonon-assisted interfacial charge modulation.