The Optoelectronic Performances And Synthesis Of Post Transition Metal Chalcogenides And Their Heterojunction

Two-dimensional materials,including single-element two-dimensional materials,transition metal chalcogenides(TMDs)and post-transition metal compounds(PTMC),have attracted much attention of researchers owing to their excellent electrical and optoelectronic properties.Among the post-transition metal compounds,In_4/3P₂Se₆ and Sn X₂(X=S,Se)have become potential two-dimensional materials because of their suitable band gap,high light absorption coefficient,earth-abundant,environmental friendliness and high chemical stability.They have been applied in many fields,such as photodetectors,field effect transistors,lithium/sodium ion batteries and catalysis.In addition,two-dimensional vertical heterojunction is easy to prepare.It can combine the advantages of each component and also generate new properties.Related research has strong theoretical vale and practical application.Thus,two-dimensional In_4/3P₂Se₆,Sn X₂ and their heterojunction were synthesized by different methods,and their optoelectronic properties were explored by constructing different types of photodetectors.This article mainly includes the following work.(1)The physical properties of the two-dimensional In_4/3P₂Se₆ and its heterojunction were firstly studied.The In_4/3P₂Se₆ crystal was prepared by the chemical vapor transmission(CVT)method.Then few-layer In_4/3P₂Se₆ nanosheets were exfoliated from the home-made crystals.The structure,optical and optoelectronic characteristics of In_4/3P₂Se₆nanosheets were explored.The uniform In_4/3P₂Se₆ nanosheets are transferred to SnS₂ nanosheets to form In_4/3P₂Se₆-SnS₂ heterojunction.The optoelectronic properties of In_4/3P₂Se₆-SnS₂ heterojunction were studied.The force between the layers of In_4/3P₂Se₆ crystal is weak van der Waals force and it has a hexagonal structure.In_4/3P₂Se₆ is a direct semiconductor material with a band gap of 1.99 e V.In_4/3P₂Se₆ based photodetector exhits a low dark current,good optoelectronic performance and a fast response time.The formed In_4/3P₂Se₆-SnS₂ heterojunction is a type II heterojunction with an obvious photovoltaic phenomenon.The short-circuit current and an open-circuit voltage of In_4/3P₂Se₆-SnS₂heterojunction is 0.12 n A and 0.27 V,respectively.The responsivity of heterojunction is 76.8 m A·W^-1under0 V.Compared with SnS₂,the dark current of In_4/3P₂Se₆-SnS₂heterojunction is very low,so the detectivity is improved by two orders of magnitude.The response time reduced from 9.8/9.6 ms to 1.7/1.6 ms.(2)SnS₂-Mo S₂ vertical heterojunction was synthesized by one-step chemical vapor deposition(CVD)method,and the electronic and optoelectronic properties of the heterojunction were discussed.The growth mechanism is firstly explored.Few-layer Mo S₂ firstly grows on Si O₂/Si substrate.SnS₂ nucleates at the three vertices and the center of the few-layers Mo S₂ triangle,grows gradually along the three sides,and finally covers the Mo S₂ triangle to form a vertical heterojunction.By adjusting the reaction conditions,a large-area diatomic layer SnS₂-Mo S₂heterojunction is obtained.The maximum length of SnS₂-Mo S₂heterojunction can reach 40?m.The interlayer charge separation of SnS₂-Mo S₂heterojunction can be seen.The device of the bilayer heterojunction exihits a high FET on/off ratio of 6.5×10~6.An obvious rectification effect also appeares and the rectification ratio is 114 when no gate voltage is applied.The mobility of SnS₂-Mo S₂ vertical heterojunction is higher than that of a single materials SnS₂ and Mo S₂.Since the formed SnS₂-Mo S₂ vertical heterojunction is a type II heterojunction,it has excellent photovoltaic performance.The short-circuit current and the open-circuit voltage of SnS₂-Mo S₂heterojunction is 0.14 n A and 0.079 V,respectively.The responsivity and the detectivity of SnS₂-Mo S₂heterojunction is 36 m A·W^-1and 1.6×10¹¹ Jones under 0 V.The response speed is also relatively fast.(3)Two-dimensional SnS₂ were firstly used for metal-semiconductor-metal(MSM)devices.Graphene-SnS₂-Au heterojunctions were prepared by a dry transfer method.The electrical and optoelectronic properties of Graphene-SnS₂-Au heterojunctions were explored.Due to the formation of an asymmetric schottky junction,the device demonstrates a good rectification effect and the rectification ratio can reach 1456.Graphene-SnS₂-Au heterojunctions also shows photovoltaic performance.The short-circuit current and the open circuit voltage of Graphene-SnS₂-Au heterojunctions is 9 p A and 0.05 V,respectively.The light responsivity and detectivity of Graphene-SnS₂-Au heterojunctions is 3.6 m A·W^-1 and 5.6×10~9Jones under 0 V.The responsivity of the device is up to 120 A·W^-1 under 1 V.The gate voltage can regulate the light responsivity and the maximum responsivity of 870 A·W^-1 is obtained.(4)SnSe_xS_2-x alloy were synthesized by chemical vapor deposition method and the corresponding optoelectronic properties were explored.The shape of as-obtained products are all semi-hexagonal with uniform size and thickness.A full-component SnSe_xS_2-x alloy is obtained by adjusting the synthesis conditions.Increasing the amount of Se and extending the reaction time can increase Se content of SnSex S2-x alloy and changing S heating temperature will adjust the Se content of SnSex S2-x in a broader range.Correspondingly,the band gap of SnSex S2-x alloy has also been adjusted,continuously changing from 2.24 e V to 1.37 e V.The obtained SnSe_xS_2-x alloy was used for the photoelectrochemical(PEC)detector for the first time.When the x vaule is fixed,the photocurrent of all SnSe_xS_2-x alloys increased with the increasing of voltage.Under the same bias voltage,SnSe_xS_2-x alloys first increased and then decreased with the increasing of Se content.SnSe_0.92S_0.99 alloy exhibits the best photoelectric performance.The maximum photocurrent,responsivity and the detectivity of SnSe_0.92S_0.99 alloy can reach 32.5?A·cm^-2,325?A·W^-1 and 1.45×10~8 Jones,respectively.