Tuning the electronic properties of bondings in monolayer MoS₂ through (Au, O) co-doping

Improving the electronic properties of Au-S bonding is the key to tuning the carrier transport of monolayer MoS₂-based nanodevices. Herein, we systematically investigate the electronic properties for Au-doped, O-doped, and (Au, O) co-doped monolayer MoS₂ to analysis the electronic properties of Au-S bondings using first-principles density functional calculations. Three gap states induced by Au-S bondings are observed at the band gap in Au-doped and (Au, O) co-doped monolayer MoS₂, which are n-type semiconductors. Moreover, the n-type barriers between the Fermi level of Au-doped and (Au, O) co-doped systems and the CBM of un-doped monolayer MoS₂ are 0.84 and 0.65 eV, respectively. In addition, low electron density and electron density difference are observed for Au-S bondings in Au-doped monolayer MoS₂, suggesting weak covalent Au-S bondings with high resistance; this explains the observed low carrier mobility of monolayer MoS₂ devices with an Au electrode. Upon introducing elemental O into Au-doped monolayer MoS₂, electron density and electron density difference of Au-S bondings in (Au, O) co-doped monolayer MoS₂ are increased to 0.58 and 0.15 eV Å^-3, respectively, showing that the covalent Au-S bondings are strengthened, and their resistance and electron injection efficiency are further improved by the elemental O dopant. Our findings may provide an effective way to improve the electronic properties of Au-S bondings in monolayer MoS₂-based nanodevices with an Au electrode.