Gas adsorbates are Coulomb scatterers, rather than neutral ones, in a monolayer MoS ₂ field effect transistor

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 (NST) 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 (Nacc) region. A decrease of both NST and the scattering parameter αSC 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 αSC ∝ Nacc-γ, as in Si-MOSFETs. Our results support that the gas adsorbates work as charged impurities, rather than neutral ones.