The Oretical Study Of Nonlinear Optical Propertics Of Graphene-like Silicon Carbide

Nonlinear optics was born after the advent of laser,and its development largely depends on the nonlinear optical materials.Thus,scientists have been looking for materials with excellent nonlinear optical performance for decades.Although graphene is a kind of optical materials with excellent nonlinear properties,it is a zero-bandgap material as well,which limits its application in optoelectronic devices.People have tried to modify the structure of graphene by various ways in order to expand the zero-bandgap.For example,silicon-doped graphene-like silicon carbide structure?g-SiC?shows obvious band gap,monolayer two-dimensional silicon carbide?2d-SiC?with 1:1 Si/C stoichiometry is a semiconductor with a large gap of 2.55 eV.2d-SiC is approximately planar,and the structure has a good?-electron delocalization.Therefore,2d-SiC may have good nonlinear optical properties.In this paper,we studied the nonlinear performance of several typical g-SiC structures by theoretical calculation from the following three parts.1.The effect of stacking and strain on the nonlinear second harmonic generation?SHG?coefficient.We constructured Bernal-stacked 2d-SiC within six layers and the SHG coefficient were studied by using the first-principles calculation.The analysis of physical origin of the SHG process shows that the single-particle transition channel formed by three bands dominates the SHG process of 2d-SiC.The interband motion of electrons is significantly tuned by intraband motion.The angle dependence of the SHG coefficient of2d-SiC is given as a reference for future experiments.A tunable SHG enhancement could be obtained by straining 2d-SiC^[1].2.The theoretical studies of the nonlinear performance of 2d-Si₂C₃,2d-SiC₃ and2d-SiC₄.We selected the most stable structures of 2d-SiC with different stoichiometric compositions?Si:C ratio=2:3,1:3 and 1:4?based on particle-swarm optimization,and studied their nonlinear second harmonic coefficients and third harmonic coefficients.All three structures have?-electron delocalized bands and they show good nonlinear performance especially 2d-SiC₄.Comparing three structures with prime 2d-SiC,the nonlinear optical properties increase with decreasing the proportion of Si atoms in the structure of g-SiC.3.Theoretical studies on the nonlinear third harmonic performance of bilayer silicon carbide?BL-SiC?and trilayer silicon carbide?TL-SiC?.Firstly,we selected monolayer silicon carbide?ML-Si C?,BL-SiC?AB-SiC?,TL-SiC?ABA-CSiC,ABA-SiCSi?and studied the effects of stacking on nonlinear third harmonic coefficients.Stacking makes the nonlinear polarization sharply increased.Secondly,we studied the effects of different stacking methods and stacking order on the nonlinear polarization of few-layers silicon carbide?FL-SiC?by BL-SiC?AA-SiC,AA-CC,AB-SiC,AB-SiSi and AB-CC?and TL-SiC?ABA-CSiC,ABA-SiCSi,ABC-SiSiCC,ABC-CSiCSi,ABC-CSiCC and ABC-SiCSiSi?.Different stacking methods and orders make different opposited atoms of FL-SiC.The interaction between different atoms affects the nonlinear performance of SiC.