Performance enhancement of monolayer MoS₂ transistors by atomic layer deposition of high-k dielectric assisted by Al₂O₃ seed layer

In this work, thermal atomic layer deposition (ALD) of HfO₂ on monolayer (ML) MoS₂ with 1 nm Al₂O₃ seed layer by e-beam evaporation was explored. With the 1 nm Al₂O₃ seed layer, a uniform HfO₂ layer can be deposited on the ML MoS₂ with bare influence on the ML MoS₂ structure. After coating a uniform HfO₂, abundant electrons are accumulated in MoS₂ and SiO₂ resulting in a high on/off current ratio of ∼10⁹ and a dramatic reduction of subthreshold swing (SS) from 1943 to 168 mV/dec of back-gated ML MoS₂ transistor on 300 nm SiO₂. A low SS of 103 mV/dec was further obtained from top-gated transistor with ∼23.3 nm HfO₂ as the gate oxide. The results manifest the beneficial influence of using 1 nm Al₂O₃ on the electrical performance of ML MoS₂ transistors, suggesting a feasible strategy for ALD of high-k dielectric layer on ML 2D materials.