Theoretical Study On Electronic Structure And Optoelectronic Properties Of Low Dimensional Semiconductor Materials

In recent years,a large number of two-dimensional(2D)materials,such as graphene,transition metal dichalcogenides(represented by Mo S₂),III-VIA group semiconductors(represented by In Se),black phosphorus(BP),and bismuth-containing ternary compounds(represented by Bi OCl)have been successfully prepared experimentally.These 2D materials show superior physical properties,such as ultra-high carrier mobility,2D superconductivity,metal-insulator transition,2D multiferroicity and other excellent physical properties.They have become an ideal platform for the research of low-dimensional physical properties and attracted extensive attention all over the world.In addition,a new class of layered materials composed of quasi one-dimensional(1D)chains was reported and provide the structural possibility to continue Moore's law,such as group I-VI-VIA semiconductors(represented by Sb Se I),group V-VIA semiconductors(represented by Sb₂Se₃),and group VIA elemental semiconductors(Se and Te).However,researches on this kind of materials are rarely reported.In addition,the design of new low dimensional functional materials is an effective means to improve the performance of materials and realize the specific functionalization of materials.In this case,a deep understanding on the correlations between structural and physical properties is needed for realizing precise design according to desired functional and properties.Therefore,in this thesis,the following research work is carried out for 2D materials and low-dimensional perovskites using first-principles calculations based on density functional theory:1.Revealing the mechanism of the different layer-dependent behavior of the electronic properties of?-Se and Sb₂Se₃.We have systematically studied the variation of the bandgap of quasi-1D layered materials?-Se and Sb₂Se₃ with the number of layers.It is found that the bandgap of?-Se decreases by?1.0 e V when the layer numbers increase from 1 to 6,while the bandgap of Sb₂Se₃ is almost unchanged.The difference of the layer-behavior of electronic properties is originated from the different interlayer/interchain coupling in?-Se and Sb₂Se₃.Strong wavefunction overlap between layer and chain at the band edge of?-Se resulting in strong interlayer/interchain coupling,while the weak wavefunction overlap leads to weak interlayer/interchain coupling of Sb₂Se₃.These results demonstrated that there are significant differences in interlayer/interchain coupling between the two quasi-1D layered materials and revealed the mechanism of its influence on physical properties.2.Demonstrating a more sensitive material,antimonene,for micro-RNA(miRNA)detection.Based on the combination of experiment and theoretical calculation,a surface plasmon resonance(SPR)sensor based on 2D materials antimonene is proved to have great potential for the label free ultra-sensitive detection of clinical biomarkers such as miRNA.The first principles calculations show that the adsorption energy and work function increment of antimony are larger than that of graphene due to the fold structure of antimony and the delocalized of Sb 5s/5p states.As a result,the detection limit reduced to the lowest reported record,which is 2.3-10000times higher than that of existing miRNA sensors.This work attempts to combine exotic sensing materials and SPR architectures as a way to explore ultra-sensitive detection of miRNA and DNA at the first time and provides a promising avenue for early diagnosis,staging and monitoring of cancer.3.Revealing the mechanism of halogen substitution on the luminescence properties of zero-dimensional(0D)hybrid perovskites.A series of 0D(C₉NH₂₀)₉Pb₃Zn₂Br_19(1-x)Cl_19x(x=0-1)compounds with large Stokes shifts and broadband emission were synthesized experimentally.Experimental measurements reveal that the luminescence color of the 0D perovskites change from yellow to green and the photoluminescence quantum yield(PLQY)increase from 8%to 91%after the Br^-substituted by Cl^-.First-principles calculations reveal that the large Stokes shifts arise from self-trapped exciton(STE)and local structural distortion of[Pb₃Br/Cl₁₁]^5-,and the tunable emissions from yellow to green originated from STE emission of[Pb₃(Br/Cl)₁₁]^5-clusters in the different chemical environment.The enhanced electron-phonon interaction and the weakened thermal-assisted de-trapped nonradiative recombination in Cl-ending compound resulting in the enhanced PLQY.This work explains the physical role of halogen ions in the photophysical process and provides a feasible way to improve the photoluminescence properties of low-dimensional hybrid materials.4.Designing tetrahedral bonding layer heterostructuring hybrid semiconductors(TB-LHHSs)functional materials and revealing the roles of organic molecules and inorganic superlattices on properties.Through the hybridization strategy,we designed a series of TB-LHHSs and studied the effects of organic molecules and the thickness of inorganic superlattice on the physical properties of TB-LHHSs.Through the structural stability screening criteria,we found that organic molecules play a decisive role in the stability of TB-LHHSs.For II-VI,III-V binary semiconductors and I-III-VI ternary semiconductors,ethylenediamine is the best filling molecule.By adjusting the thickness of the inorganic superlattice,the bandgap,optical absorption and effective masses of TB-LHHSs can be effectively modeled.Importantly,we found?/?-(In₂As₂)_nen(n=3-5)is an ideal absorbing materials for solar cells with strong absorption intensity,smaller carrier effective mass(0.024 m₀<me<0.11 m₀)and higher“spectroscopic limited maximum efficiency”(SLME)(beyond 30%).The II-VI group based TB-LHHSs,?/?-(Zn₂Se₂)_nen(n=1-6)and?/?-(Zn₂Te₂)_nen(n=1-6),with large bandgap(2.50 e V-4.11 e V)and significant anisotropy transport properties are potential candidates as room temperature detecting and ultraviolet detecting materials.The significant anisotropy of optical absorption and effective masses of thermal stable TB-LHHSs gives potential as optical switches and modulator candidates.This work provides new insights into the design of functional materials and reveals the laws affecting the structural stability and physical properties in TB-LHHSs.