Monolayer MoS2-based transistors with low contact resistance by inserting ultrathin Al2O3 interfacial layer

Transition metal dichalcogenides(TMDCs)are promising high performance electronic materials due to their interesting semiconductor properties. However, it is acknowledged that the effective electrical contact between TMDCs-layered materials and metals remains one of the major challenges. In this work, the homogeneous monolayer MoS2films with high crystalline quality were prepared by chemical vapor deposition method on SiO2/Si substrates. The back-gate field-effect transistors(FETs)were fabricated by inserting an ultrathin Al2O3interlayer between the metal electrodes and MoS2nanosheets. With the addition of an ultrathin 0.8 nm Al2O3interlayer, the contact resistance decreased dramatically from 59.9 to 1.3 kΩ μm and the Schottky barrier height(SBH)dropped from 102 to 27 meV compared with devices without the Al2O3interlayer. At the same time, the switching ratio increased from ～106to ～108, and both the on-current and field-effect mobility were greatly improved. We find that the ultrathin Al2O3interlayer can not only reduce the SBH to alleviate the Fermi level pinning phenomenon at the interface,but also protect the channel materials from the influence of air and moisture as a covering layer. In addition, the lattice and band structures of Al2O3/MoS2film were calculated and analyzed by first-principles calculation. It is found that the total density of states of the Al2O3/MoS2film exhibits interfacial polarized metals property, which proves the higher carrier transport characteristics. FETs with Al2O3interlayers have excellent stability and repeatability, which can provide effective references for future low power and high performance electronic devices.