High-Performance Monolayer MoS₂ Field-Effect Transistors on Cyclic Olefin Copolymer-Passivated SiO₂ Gate Dielectric

Trap states of the semiconductor/gate dielectric interface give rise to a pronounced subthreshold behavior in field-effect transistors (FETs) diminishing and masking intrinsic properties of 2D materials. To reduce the well-known detrimental effect of SiO₂ surface traps, this work spin-coated an ultrathin (≈5 nm) cyclic olefin copolymer (COC) layer onto the oxide and this hydrophobic layer acts as a surface passivator. The chemical resistance of COC allows to fabricate monolayer MoS₂ FETs on SiO₂ by standard cleanroom processes. This way, the interface trap density is lowered and stabilized almost fivefold, to around 5 × 10¹¹ cm⁻² eV⁻¹, which enables low-voltage FETs even on 300 nm thick SiO₂. In addition to this superior electrical performance, the photoresponsivity of the MoS₂ devices on passivated oxide is also enhanced by four orders of magnitude compared to nonpassivated MoS₂ FETs. Under these conditions, negative photoconductivity and a photoresponsivity of 3 × 10⁷ A W⁻¹ is observed which is a new highest value for MoS₂. These findings indicate that the ultrathin COC passivation of the gate dielectric enables to probe exciting properties of the atomically thin 2D semiconductor, rather than interface trap dominated effects.