First-Principles Study On Optoelectronic Properties Of Hexagonal Boron Nitride With Point Defect And Doping

Hexagonal boron nitride is a two-dimensional III-V nitride semiconductor material.It has excellent advantages such as wide band gap,high hardness,high thermal conductivity and corrosion resistance.It is very useful in the fields of optoelectronic devices,high-frequency communication and power conversion.Great application potential.As a semiconductor material,defects and impurities will have a significant impact on the properties of hexagonal boron nitride.Point defects are the most basic type of defects,and doping is an important means to change the properties of materials,which has great research value.However,the current research on hexagonal boron nitride point defects is not comprehensive,and there is a lack of research on substitution defects.For p-type and n-type doping studies,there is a problem of too few impurity elements being studied.At the same time,there is a lack of research on the effects of defects and impurities on the optical properties of hexagonal boron nitride.This paper studies the electronic and optical properties of ideal hexagonal boron nitride nanosheets with four intrinsic point defects and two types of doping,which provides a richer theoretical basis for the application of hexagonal boron nitride in optoelectronic devices.The research content of this paper includes: In the first-principle calculation software,the plane wave pseudopotential method based on density functional theory is used to respectively contain four kinds of intrinsic point defects,five kinds of p-type doping and five kinds of n-type doping The hexagonal boron nitride nanosheets were structurally optimized to observe their effect on the internal structure of hexagonal boron nitride and calculate the corresponding electronic and optical properties.The four types of intrinsic point defects include: B vacancy(VB),N vacancy(VN),B replacing N(BN)and N replacing B(NB).The five types of p-type impurities include: Li,Na,and Mg replacing B atoms and Si and C instead of N atoms.Among them,Li,Na,and Si are p-type doping of hexagonal boron nitride for the first time.The five types of n-type impurities include: C replacing B atoms and O,S,Se,and Cl replacing N atoms,where Se and Cl are the n-type doping of hexagonal boron nitride for the first time.Electronic properties include: band structure,total state density,partial wave state density,and differential charge density.Optical properties include complex dielectric function,complex refractive index,reflectivity,absorption spectrum and electron energy loss spectrum in two directions parallel and perpendicular to the material plane.In the study of the four intrinsic point defects of hexagonal boron nitride,the calculation results show that: by comparing the formation energy of various point defects in B-rich and N-rich environments,it can be known that replacement defects are always easier to form than vacancy defects,And VN defects are always easier to form than VB defects.VB defects will destroy the flatness of the atomic arrangement,while other defects have no such phenomenon.Intrinsic hexagonal boron nitride is a weak p-type indirect bandgap semiconductor.VN defects will make hexagonal boron nitride exhibit n-type characteristics,and the remaining three defects will enhance the p-type characteristics of the material.The effect of various point defects on hexagonal boron nitride is limited to the direction parallel to the material plane.Intrinsic hexagonal boron nitride has excellent passability for light with a photon energy of 0-6 e V.A higher absorption peak is introduced in the VB defect interval,and the remaining defects have a relatively small effect.The VB defect causes a large oscillation in the reflectivity and refractive index in 0-6 e V.The remaining defects increase the reflectivity and refractive index in this interval slightly.Overall,the VB defect enhances the p-type characteristics of hexagonal boron nitride and significantly improves the ability of hexagonal boron nitride to absorb violet light and nearultraviolet light,and can be used in light detection elements in the corresponding band.The remaining defects have little effect on the optical properties,and can assist n-type or p-type doping in light-emitting elements with frequencies up to the deep ultraviolet band.In the study of the two types of doping of hexagonal boron nitride,the internal structure optimization results show that Li doping will significantly destroy the flatness of the atomic arrangement,thereby reducing the structural stability.C as a p-type impurity or n-type impurity has the smallest effect on the internal structure.The calculation results of various properties show that: among p-type impurities,Li,Na,and C introduce the impurity level closest to the valence band;among n-type impurities,C,Se,and Cl introduce the impurity level closest to the conduction band.Among them,Cl doping will change the energy band structure of the material,making it into a direct band gap semiconductor.The effect of doping on the optical properties of hexagonal boron nitride is reflected in the low energy region of 0-6 e V parallel to the material plane.Among them,Mg and C in p-type impurities and Se and Cl in n-type impurities have the largest influence.Not only does it introduce a higher absorption peak in the low-energy region,but also makes the reflectivity and refractive index in this interval violent.All in all,from the perspective of internal structural stability and energy band structure,Na and C in p-type impurities and Se and Cl in n-type impurities are the most ideal.While obtaining strong doping characteristics,they ensure that Stability of internal structure.These four kinds of doping can be used for light emitting devices in the deep ultraviolet band.In addition,p-type C doping is also suitable for photodetectors in the violet or near-ultraviolet band;n-type Se and Cl are suitable for photodetectors in part of the visible and infrared bands.