Low-frequency noise in multilayer MoS2 field-effect transistors: the effect of high-k passivation

Abstract

Diagnosing of the interface quality and the interactions between insulators and semiconductors is significant to achieve the high performance of nanodevices. Herein, low-frequency noise (LFN) in mechanically exfoliated multilayer molybdenum disulfide (MoS₂) (∼11.3 nm-thick) field-effect transistors with back-gate control was characterized with and without an Al₂O₃ high-k passivation layer. The carrier number fluctuation (CNF) model associated with trapping/detrapping the charge carriers at the interface nicely described the noise behavior in the strong accumulation regime both with and without the Al₂O₃ passivation layer. The interface trap density at the MoS₂–SiO₂ interface was extracted from the LFN analysis, and estimated to be N_it ∼ 10¹⁰ eV⁻¹ cm⁻² without and with the passivation layer. This suggested that the accumulation channel induced by the back-gate was not significantly influenced by the passivation layer. The Hooge mobility fluctuation (HMF) model implying the bulk conduction was found to describe the drain current fluctuations in the subthreshold regime, which is rarely observed in other nanodevices, attributed to those extremely thin channel sizes. In the case of the thick-MoS₂ (∼40 nm-thick) without the passivation, the HMF model was clearly observed all over the operation regime, ensuring the existence of the bulk conduction in multilayer MoS₂. With the Al₂O₃ passivation layer, the change in the noise behavior was explained from the point of formation of the additional top channel in the MoS₂ because of the fixed charges in the Al₂O₃. The interface trap density from the additional CNF model was N_it = 1.8 × 10¹² eV⁻¹ cm⁻² at the MoS₂–Al₂O₃ interface.