Preparation And Electrical Properties Of MoS₂/VO₂ Heterojunction

Molybdenum disulfide(MoS₂)as another kind of two-dimensional materials after the discovery of graphene,graphene not only has a layered structure similar to graphene,but also has a natural tunable band gap(from 1.3e V indirect band gap of bulk materials to 1.8e V direct band gap of single layer).Due to its excellent semiconductor properties,field effect transistors,photodetectors and other aspects show great application potential.Vanadium dioxide(VO₂)thin films will produce semiconductor metal phase transition at about 68?,from monoclinic phase to tetragonal rutile phase.At the same time,with the change of photoelectric properties,VO₂thin films have potential applications in optoelectronic devices.In this paper,MoS₂thin films with large area and high quality were prepared by controlling the pyrolysis conditions in tubular furnace.Then VO₂thin films with phase transition properties were prepared by magnetron sputtering.Finally,MoS₂/VO₂heterojunction was prepared by PMMA assisted transfer.In this paper,(NH₄)₂MoS₄precursor films were prepared on SiO₂/Sisubstrates,and the effects of solution concentration,different rotation speed and the addition of polyvinyl alcohol(PVA)on the precursor films were studied.Then MoS₂thin films were prepared by pyrolysis in a tubular furnace,and the effects of pyrolysis conditions on the content and crystallinity of MoS₂were studied.During the preparation of(NH₄)₂MoS₄,with the increase of solution concentration and spin coating speed,the(NH₄)₂MoS₄particles on SiO₂/Sisubstrate gradually agglomerate,but it is difficult to form a continuous film.Finally,a continuous film is formed by adding PVA;Then(NH₄)₂MoS₄thin film was pyrolyzed in tubular furnace.In the process of pyrolysis,only MoO₃thin film was obtained by adding10%H₂/Ar in vacuum and O₂in tubular furnace.MoS₂,MoO₂and MoO₃mixed films were obtained by adding 10%H₂/Ar and S powder under atmospheric pressure.High quality MoS₂thin films were obtained by adding 10%H₂/Ar and S powder under normal pressure.Finally,the prepared MoS₂thin films have good crystallinity and layered structure,and can realize large area film transfer.Then VO₂thin films were deposited on SiO₂/Sisubstrates by magnetron sputtering.The crystallinity of VO₂thin films was improved by annealing in tubular furnace.The effects of different targets,oxygen flow rate during sputtering,annealing temperature and time on the preparation of VO₂thin films were studied.The results show that V₂O₅is the main film prepared by metal V target,and the surface is rough after annealing,so it is difficult to obtain single VO₂;Using VO₂target,with the increase of oxygen flow rate,the oxygen content of the film increases,with the increase of annealing temperature,the crystallinity of the film increases,and the film changes from VO₂(B)to VO₂(M).Finally,VO₂(M)film is obtained after annealing at 1 sccm oxygen flow rate,10 Pa vacuum and 500?for 1 h,and the resistivity change before and after phase change is about 2.5 orders of magnitude.Finally,MoS₂/VO₂heterojunction was prepared by PMMA assisted transfer,and Ag electrode was prepared by electron beam evaporation.The I-V characteristic curve of the transferred MoS₂film increases linearly,indicating that the Ag electrode is in good contact with the film and the contact resistance is small;MoS₂/VO₂heterostructures have rectifying properties,which may be due to the relationship between impurities and defects.The rectifying properties of MoS₂/VO₂heterostructures have no obvious influence before and after VO₂phase transition.