Study On 2D TMDCs Luminescence Modulation By Graphene Joule Heating

The facile control of luminous wavelength is of great significance in the fields of on-chip interconnection,super-resolution imaging and optical communication.Joule heating effect caused by electric current is widely applied in modulating the refractive index of silicon-based waveguides and wavelength modulation for reconfigurable nanophotonic circuits.Graphene has excellent thermal conductivity,and it can withstand extremely high current densities,making it a perfect platform for studying joule thermal effect in micro-nano scale.As a result,transition metal dichalcogenides（TMDCs）and graphene are combined in this work to create a TMDCs-graphene van der Waals heterojunction device.The Joule heat effect on graphene generates a local high-temperature,and the band gap of the TMDCs material is adjusted,allowing for a reversible tuning on the light emission wavelength of the device.The following are the key findings of this paper:（1）Firstly,graphene,Mo S₂ and WS₂ were prepared by oxygen plasma-assisted mechanical exfoliation and chemical vapor deposition（CVD）methods;secondly,TMDCs-graphene van der Waals heterojunctions were prepared by transfer techniques such as PDMS exfoliation and liquid wedging.Finally,the devices were fabricated by UV lithography,electron beam lithography,electron beam evaporation and inductively coupled plasma etching.The prepared materials and heterojunction devices were tested and characterized by optical microscopy,Raman spectroscopy,photoluminescence spectroscopy,atomic force microscopy and other equipment and methods.The test results proved that the prepared materials were more uniform without wrinkles and cracks.（2）The Joule heating effect was studied through applying voltage on biased graphene devices with Raman spectroscopy and infrared microscope.When the applied bias voltage of the graphene device increases to about 30 V,the source-drain current becomes saturated,and the resistance increases by 1 kΩ.And the carrier mobility is reduced.The temperature of suspended graphene devices reached 700k under the applied voltage of 2.5 V and that of non-suspended graphene devices reached 550K under the applied voltage of 42 V.It maintained good stability in vacuum and air environment.（3）The Raman and photoluminescence spectra of TMDCs graphene devices under applied voltage were measured by using the homemade integrated test system of electrical and Raman spectrometer.By utilizing localized Joule heating on the biased graphene and applying a moderate electric field of 6.5 k V·cm^-1 to the graphene substrate,the PL wavelength of 2D-TMDC exhibits a continuous tunning range from662 nm to 690 nm,corresponding to a bandgap reduction of 76 me V.The electric control is highly reversible during sweeping the bias back and forth.The increase of the applied electric field resulted in a significant prolongation of the photoluminescence lifetime of TMDCs.Both mechanical stripping materials and chemical vapor deposition growth materials can reproduce the luminous wavelength tuning behavior,which provides a new research idea for the electronically controlled wavelength tunable optical emitters integrated on the chip.