Preparation And Electrical Properties Of Two-dimensional SnSe₂ Single-crystal Thin Flakes And Its Field Effect Transistors

Recently,layered two-dimensional materials like graphene have been attracting extensive attention due to their unique structures and excellent performances.As a member of two-dimensional materials,two-dimensional IV-VI compounds have been indicated to be ultra-thin single-layer thickness,adjustable band gaps and novel physical properties,on the other hand,their elements are rich in earth and environmentally friendly.And hence they have exhibited the extensive application prospects for electronics and optoelectronics.SnSe2,as one of the typical IV-VI compounds,is our research object in this thesis,in which SnSe2 single crystal flakes were first synthesized by chemical vapor deposition(CVD)method,and then their morphology,field effect and annealing characteristics were studied and discussed.Firstly,a large area of SnSe2 single crystal flakes are synthesized on the mica substrates by CVD method.Then we investigate the effects of Ar/H2 ratio and reaction pressure on the growth of SnSe2 single crystal,and characterize their surface morphology,crystal structure and quality via the way of optical microscope,atomic force microscope,electron microscope,Raman spectrometer and so on.Secondly,the SnSe2 field effect transistors(FETs)are successfully fabricated on the p-type single crystal silicon substrates deposited with 300nm SiO2 by the UV lithography and electron beam evaporation.Then we measure detailedly their field effect characteristics at room temperature.It is found that the hole carriers are dominant in the as-grown SnSe2 single crystal flakes grown.Furthermore,SnSe2 FETs can be turned off at room temperature that is firstly observed in SnSe2 FETs up to now as is known to all.And besides,its on/off ratio and mobility can be up to about 105 and 40cm2/Vs,respectively.Finally,we discuss the reasons for achieving room temperature shutdown characteristics of SnSe2 FETs.Thirdly,the effects of annealing temperatures on the surface morphology,crystal structure and quality of SnSe2 single crystal flakes as well as the electrical properties of SnSe2 FETs are investigated.After annealing at 300? and 350?,the source-drain current of SnSe2 FETs is reduce by 2-10 times and the on/off ratio increased about an order of magnitude.After annealing at 400?,SnSe2 FETs are changed to be p-type.In addition,the effect of hydrogen annealing on SnSe2 FETs are also initially studied,indicating that the source-drain current increased about an order of magnitude.