The Magneto-photoluminescence Of Monolayer Transition Metal Dichalcogenide Semiconductor

In comparison with graphene,two-dimensional?2D?transition-metal dichalco-genides?TMDCs?exhibit strong spin-orbital coupling and inversion symmetry break-ing,resulting in special valley features.The introduced valley degree of freedom allows the separate manipulation of valleys located at±K points in brillouin zone,offering a platform to realize information storing and processing based on valleytronics.In ad-dition,certain TMDCs also exhibit high mobility,high on/off ratio and high detection response speed at room temperature,thus showing potential in the application ranging from integrated logical devices to photoelectric detection.We improved the technique of exfoliation and exfoliated large-area monolayer TMDCs?MoS₂,WS₂,WSe₂?,then fabricated nano-devices?FETs?based on these mono-layer materials.In the process of cryogenic magneto-photoluminescence measurement,we investigated and verified the previously reported physics in 2D TMDCs.Besides,We observed some anomalous phenomena in the measurement of cryogenic magneto-photoluminescence,which were likely attributed to the defect-induced properties.Our experiments were carried out in the presence of vertical magnetic in a cryo-genic?4 K?vacuum cryostat.We employed linearly polarized,left and right-circularly polarized laser with 532 nm wavelength,respectively,to excite monolayer TMDCs.Through collecting-K?+K?valley related left?right?-circularly polarized photolumi-nescence,we investigated valley-dependent optical selection rule,strong spin-orbital coupling and orbital hybridization.We also investigated photoluminescence mecha-nism by measuring power,temperature and magnetic-dependent PL spectra.An extremely large Zeeman splitting was observed on a defective bilayer WS₂,which was likely attributed to the coupling between layers,resulting from inversion symmetry breaking induced by high density of defects.This observed g-factor can reach 16 which is in agreement with the calculation based on the model of the intervalley transition.We also observed anomalous diamagnetism on a monolayer MoS₂and this phe-nomenon was confirmed at three different positions.We elaborated the underlying mechanism in accordance with two dimensional harmonic oscillator and quantum dots.Defects can trap electrons,holes and excitons,thus having influence on the prop-erties of 2D TMDCs.Localization of carriers'wave function becomes stronger as the dimensionality of TMDCs reduces,as a result,the effect of defects increases.Our inves-tigation into widely existing defects in TMDCs is of importance to material engineering and defect engineering.