Optoelectronic Properties of MoS2 Monolayer/Multilayer Lateral Heterojunction

The spin/valley degree of freedom and the bandgap in visible light range make MoS2 a promising material for optoelectronic applications. Several groups have reported construction of p-n junction based on Transition-Metal Dichalcogenide (TMD) recently. In this thesis, a new architecture – lateal heterojunction – based on MoS2 is demonstrated. The optoelectronic properties of the lateal heterostructure is determined by the difference of intrinsic band structures of monolalyer and multilayer MoS2. The lateralheterojunction devices are realized by choosing monolayer/multilayer MoS2 after mechanical exfoliation. The existence of built-in field is examined by Kelvin Probe Force Microscope (KPFM), photocurrent mapping at off state, bias-voltage dependent photocurrent mapping, and the asymmetric J-V curve. The photovoltaic effect is observed by performing photocurrent mapping and J-V curve under illumination. Prompt optical switching with robust performance are observed. From the back-gate voltage dependent photocurrent mapping and J-V curves, we achieve the modulation of band alignment by global gating. We observed the enhanced photocurrent at the interface as back-gate voltage lowered and the J-V curve grew linear as back-gate voltage increased, both suggesting that the the Fermi level of monolayer MoS2 is more sensitive to the back-gate voltage. The realization of the lateral heterojunction based on the novel two-dimensional TMD materials and the band alignment modulation by global gating open the avenue to both physical research and technological applications.