Preparation Of Two-dimensional Bismuth Antimonide And Characterization On Its Electrical And Thermoelectric Properties

As a topological insulator,Bi_100-xSb_xhas composition-dependent semiconductor band structure,high conductivity and low thermal conductivity,holding great potential in thermoelectric devices,topological spintronic devices and other fields.When the thickness of Bi_100-xSb_xis below 30 nm,i.e.two-dimensional（2D）Bi_100-xSb_x,intriguing electrical and thermoelectric properties will arise due to the quantum confined effect,and it is expected to be applied in micro-nano electronic devices.However,there is still a lack of cost-effective preparation methods of 2D Bi_100-xSb_x,and its electrical and thermoelectric properties need to be further studied.In this paper,continuous and uniform 2D Bi_100-xSb_xwith high preferred orientation were deposited by electron beam evaporation using home-made Bi_100-xSb_xtarget,its electrical and thermoelectric properties were intensively studied.The main results are as follows:（1）Bi_100-xSb_xtarget were obtained by melting Bi and BiSb particles.2D Bi_100-xSb_x（0≤x≤35）with thickness of 5 nm-47 nm were deposited on SiO₂/Si substrate by electron beam evaporation.The films are continuous and uniform,showing good crystallinity and high（00l）preferred orientation.The electrical conductivity of 17 nm Bi_100-xSb_xshows semiconductor behavior with a bandgap up to 183 meV at room temperature.The 2D Bi₉₃Sb₇FET shows a mobility of 33 cm²V^-1s^-1and p-type nature.The thermoelectric parameters of 2D Bi_100-xSb_xis sensitive to Sb composition.The electrical conductivity is higher than 10⁵S m^-1,the absolute value of the Seebeck coefficient reaches the maximum value(25.4μV K^-1)at x=11,the thermal conductivity reaches the lowest value(0.23 W m^-1k^-1)at x=18,and the maximum value of ZT（0.058）is also obtained in Bi₈₂Sb₁₈.（2）The thermoelectric properties of 2D Bi_100-xSb_xwas tuned by micro-nano morphology.Sublimation occurred in 2D Bi_100-xSb_xafter annealing at 250℃for 1 h,resulting in randomly distributed micropores.Because of the enhanced carrier scattering caused by the boundary of micropores,the electrical conductivity of 2D Bi_100-xSb_xdecreases.At the same time,its Seebeck coefficient is increased due to the energy filtering effect and hybridization of surface state.As for 2D Bi₈₂Sb₁₈,the absolute value of Seebeck coefficient(33.0μV K^-1)increased by84%,and its corresponding ZT value（0.13）increased by 124%.By adjusting the Ar flow rate during annealing,the size and number of sublimated micropores as well as Seebeck coefficient could be tuned,which provides a convenient method to enhance the thermoelectric performance of 2D material.Regular micro-nano morphology was generated by photolithography.Due to the large diameter（>100μm）of the pores derived from the existing process,the thermoelectric properties of 2D Bi_100-xSb_xdid not get significant improvement,and further research is needed.（3）Thickness and substrate have an effect on the the structure,morphology and thermoelectric properties of 2D Bi_100-xSb_x.As the thickness added,the crystallinity,the size of nano grains and grains on the surface of the film gradually become larger.The Seebeck coefficient shows increase trend,but the electrical conductivity does not change monotonically when the thickness increases due to the surface state transport.After annealing,the morphology of samples with different thickness varies a lot.The Seebeck coefficient increases in sample which has obvious micropores,and the calculated power factor increases with the thickness.In addition,the substrate also influences the structure,morphology and thermoelectric parameters of 2D Bi_100-xSb_x.By investigating and improving the electrical and thermoelectric properties of 2D Bi_100-xSb_x,this paper provides an experimental basis for the potential applications in heat dissipation of large-scale integrated circuits,green energy materials,spintronic devices and other fields.