Gas adsorbates are Coulomb scatterers, rather than neutral ones, in a monolayer MoS2 field effect transistor

Abstract

Direct current (DC) and low-frequency (LF) noise analyses of a chemical vapor deposition (CVD)-grown monolayer MoS₂ field effect transistor (FET) indicate that time-varying carrier perturbations originate from gas adsorbates. The LF noise analysis supports that the natural desorption of physisorbed gas molecules, water and oxygen, largely reduces the interface trap density (N_ST) under vacuum conditions (∼10⁻⁸ Torr) for 2 weeks. After a longer period of 8 months under vacuum, the carrier scattering mechanism alters, in particular for the low carrier density (N_acc) region. A decrease of both N_ST and the scattering parameter α_SC with desorption of surface adsorbates from MoS₂, explains the enhanced carrier mobility and the early turn-on of the device. The stabilized carrier behavior is verified with γ = 0.5 in the formula α_SC ∝ N_acc^−γ, as in Si-MOSFETs. Our results support that the gas adsorbates work as charged impurities, rather than neutral ones.