Study On The Light Enhancement Mechanism Of Two-dimensional Silicene/gallium Selenide

In recent years,with the successful preparation of graphene,two-dimensional（2D）materials have attracted extensive attention from the scientific community due to their excellent physical and chemical properties.As the silicon equivalent of graphene,silicene has been widely studied because of its better compatibility with today’s silicon-based electronic devices,and has been successfully applied to micro-nano electronic devices.However,the zero bandgap and low optical absorption of silicene severely limit its application in nano-optoelectronic devices.2D GaSe has the same hexagonal symmetric structure as silicene,and is widely used in photodetectors due to its excellent photoelectric properties.However,the large bandgap of2D GaSe limits its light absorption ability for visible light.Based on the first-principles of density functional theory,this paper uses halogen atoms（F,Cl,Br,I）to chemically functionalize silicene and construct 2D GaP/GaSe van der Waals heterojunction（vdWH）,respectively and adjusted the electronic and optical properties of silicene and 2D GaSe respectively,and carried out a detailed theoretical analysis of the electronic and optical properties of halogenated silicene and 2D GaP/GaSe vdWH.The main research contents are as follows:（1）Based on DFT first-principles calculations,this paper uses halogen atoms to chemically functionalize silicene.The calculated electronic properties show that full-and Janus-functionalization successfully open the bandgap of pristine silicene,which varied from0.544 to 1.276 e V by the PBE method,and from 1.390 to 2.123 e V by the HSE06 method.Half-functionalization enables silicene with metallic behavior but retains semiconducting properties with a relatively large bandgap.Importantly,by means of electron density distribution,electron density difference（EDD）and mulliken population analysis,the results of full-and Janus-functionalization suggest that the halogenation weakens the covalent strength of the Si-Si bond in the silicene monolayer but still maintains the covalent character,and chemical bond X1（X2）-Si1（Si2）is predominantly ionic and ionicity decreases with the increasing halogen atomic periodic number.The chemical bond X1（X2）-Si1（Si2）in the half-functionalized monolayers is also dominated by ionicity.The calculated optical properties show that F–Si monolayer reaches a maximum value of 84400 cm^-1 at 4.04 e V.halogenation also has a certain modulation effect on the light absorption of silicene in the energy region of 2.47-4.64 e V,and the modulation is more pronounced in the UV region.（2）Based on DFT first-principles calculations,a 2D GaP/GaSe vdWH with type-II band alignment is constructed in this paper.The results show 2D GaP/GaSe vdWH is an indirect bandgap semiconductor with a bandgap of 1.59 e V and high carrier mobility,which exhibits excellent anisotropy along theΓ-X andΓ-Y directions.The electron and hole mobilities of GaP/GaSe vdWH were calculated to be 5891.42 cm²V^-1S^-1 and 7944.29 cm²V^-1S^-1,respectively.The hole mobility of 2D GaP/GaSe vdWH can achieve 129891.12 cm²V^-1S^-1 at-2%compressive strain.The 2D GaP/GaSe vdWH has a calculated exciton binding energy of 0.35e V and absorbs electromagnetic radiation more widely than both monolayers,especially for infrared light absorption.Therefore,the constructed 2D GaP/GaSe vdWH is a competitive candidate for optoelectric nanodevices.