Millimeter-scale layered MoSe₂ grown on sapphire and evidence for negative magnetoresistance

Molecular beam epitaxy technique has been used to deposit a single layer and a bilayer of MoSe₂ on sapphire. Extensive characterizations including in-situ and ex-situ measurements show that the layered MoSe₂ grows in a scalable manner on the substrate and reveals characteristics of a stoichiometric 2H-phase. The layered MoSe₂ exhibits polycrystalline features with domains separated by defects and boundaries. Temperature and magnetic field dependent resistivity measurements unveil a carrier hopping character described within two-dimensional variable range hopping mechanism. Moreover, a negative magnetoresistance was observed, stressing a fascinating feature of the charge transport under the application of a magnetic field in the layered MoSe₂ system. This negative magnetoresistance observed at millimeter-scale is similar to that observed recently at room temperature in WS₂ flakes at a micrometer scale [Zhang et al., Appl. Phys. Lett. 108, 153114 (2016)]. This scalability highlights the fact that the underlying physical mechanism is intrinsic to these two-dimensional materials and occurs at very short scale.