Photoelectronic Properties Of MoSi₂N₄ Based Heterostructures

In recent years,two-dimensional materials have attracted much attention due to their excellent properties and broad application prospects,especially after the discovery of graphene,a breakthrough has been made.Van der Waals heterostructures composed of two-dimensional semiconductor materials are widely used because they can retain the properties of two-dimensional materials.Semiconductor heterostructures are an important part of solid-state physics,which can adjust and control the parameters of semiconductor crystals and devices.Electronic devices based on heterostructures are widely used in many fields of life,bringing great important change to our daily life.In this paper,the electrical and optical properties of two vertical van der Waals heterojunctions,Cs Pb I₃/Mo Si₂N₄ and Cs₃Bi₂I₉/Mo Si₂N₄were deeply studied by first-principles calculations.Firstly,this paper studies the Cs Pb I₃/Mo Si₂N₄ heterostructure.In recent years,Cs Pb I₃ inorganic perovskites without any volatile organic components have attracted much attention due to their excellent chemical stability and suitable band gap.Cs Pb I ₃is considered to be one of the most promising photovoltaic materials among all Cs Pb X₃（X=Cl,Br,I）,which has a suitable optical absorption range and excellent optoelectronic properties,which can greatly reduce the thickness to effectively promote the utilization of photons.Despite the excellent performance of the all-inorganic perovskite Cs Pb I₃ device,it still has some properties lower than that of the hybrid perovskite device.Mo Si₂N₄ is an indirect bandgap semiconductor with extraordinary environmental stability and high electron-hole mobility.In this paper,Cs Pb I₃/Mo Si₂N₄ heterostructures with different terminated interfaces（Cs-I terminated and Pb-I terminated）were constructed and systematically studied by first-principles calculations.The stability of the heterostructure is ensured by the calculation of its binding energy,and the results show that the electronic band structures of monolayer Cs Pb I₃ and monolayer Mo Si₂N₄ are almost preserved in the Cs Pb I₃/Mo Si₂N₄heterostructure.The Cs Pb I₃/Mo Si₂N₄ heterostructure with Cs-I and Pb-I as the terminal contact interface has an indirect band gap of 0.60 e V and a direct band gap of0.80 e V,respectively.Both heterostructures exhibit a type II band alignment.It shows that it can effectively promote the spatial separation of photogenerated carriers.Through the study of optical absorption spectrum,it is found that in the Cs Pb I₃/Mo Si₂N₄ heterostructure for Cs-I terminated,the optical absorption coefficient is enhanced in the ultraviolet region;the Cs Pb I₃/Mo Si₂N₄ heterostructure for Pb-I terminated,the optical absorption spectrum is enhanced to varying degrees in the whole region,especially in the visible light region.In conclusion,the Cs Pb I₃/Mo Si₂N₄heterostructure has important potential in the application field of optoelectronic devices.Secondly,this paper studies the Cs₃Bi₂I₉/Mo Si₂N₄ heterostructure.The two-dimensional trivalent metal-based ternary halide perovskite A₃B₂X₉（A=MA,Cs;B=Bi,Sb;X=Cl,Br,I）is considered to be a promising material for high-performance photovoltaic applications.In addition,bismuth-based perovskites exhibit better stability and broader photovoltaic applications.In this paper,the structural stability,electronic properties,charge transport mechanism and optical properties of two-dimensional Cs₃Bi₂I₉/Mo Si₂N₄ van der Waals heterostructures were theoretically investigated by using first-principles calculations.The results show that the two-dimensional Cs₃Bi₂I₉/Mo Si₂N₄ heterostructure has a direct band gap and a type II band alignment,which is due to the built-in electric field caused by the electron transfer from the Mo Si₂N₄ layer to the Cs₃Bi₂I₉ layer,which can prevent the recombination photogenerated electrons and photogenerated holes,thereby,increasing the carrier lifetime.In addition,the heterostructures have enhanced optical absorption in the visible and ultraviolet regions,and their electronic properties can be tuned by in-plane strain with obvious metal-semiconductor transitions.Finally,we explore more A₃B₂X₉/MA₂Z₄ van der Waals heterostructures（where,in A₃B₂X₉,A=Cs;B=In,Sb;X=Cl,Br,I;in MA₂Z₄,A=N,P;M=Cr,Mo,Ti）and found heterostructures of all band alignment types（type I,type II and type III）.Above all,our study provides a comprehensive theoretical understanding of the electrical and optical properties of perovskite-based heterostructures and suggests their potential applications in optoelectronic devices.