Properties Of Two-dimensional TMDs Photodetector

Two-dimensional transition metal dichalcogenides(TMDs)have been proven to possess high carrier mobility,band gap ideal for ultraviolet to near-infrared spectrum detection and band structure related to the number of layers,etc.,which are of great benefit to application to photodetectors.So far,a series of TMDs-based photodetectors with excellent properties have been achieved.However,most of their preparation techniques used are reported to be exfoliation or chemical vapor deposition which have disadvantages of small and uncontrollable sizes,limited scale and unclean process.To date,a large number of reports on TMDs-based photodetectors are mainly based on materials such as molybdenum disulfide,molybdenum diselenide and tungsten disulfide.Research on tungsten diselenide(WSe₂)is not very extensive,but this material is also worth studying.In this thesis,a review of development of pulsed laser deposition(PLD)in photodetection is firstly carried out.PLD is a type of physical vapor deposition technique which can transfer the target material to substrates according to stoichiometric ratio.In addition,the technique parameters are intuitive,and the process is clean,which make PLD an ideal method for preparing large-scale zero-,one-and two-dimensional materials.The review expands on series of materials including TMDs.The characteristics,advantages and conventional preparation methods of these materials are introduced in detail,and the superiorities of using PLD to prepare them are pointed out.Also,reports on PLD application to photodetctors are listed.Two-dimensional WSe₂,as a member of TMDs,has similar properties to others of those,such as strong light-matter interaction and band structure related to number of layers,which make it a promising materials for photodetectors.In this thesis,a few-layered WSe2 nanosheet is prepared by mechanical exfoliation to study the performance in photodetector application.The WSe₂ pohotodetector based on photoconductive effect shows stable response in visible to ultraviolet light spectrum.Favourable responsivity(8.573 A W-1)and high detectivity(1.210×1010 Jones)are obtained,and response time of only 120 ms is achieved.The results prove that two-dimensional WSe2 has great potential in application to photodetectors.Considering the advantages of PLD in large-scale production and the lack of reports on TMDs-based photodetectors realized by PLD,achieving the combination of those above will be of great significance to the development of photodetectors based on two-dimensional materials.