The Structures And Properties Study Of Two-dimensional Materials Based On Group VA Elements

With the emergence of graphene,two-dimensional(2D)atomic-layer materials have gained a wide range of concern.Recently,the mainly found 2D layered nano materials are: siliconene,germaninene,h-BN,Mo S2,WS2,Pb I,Mo Cl,Mn O2,Wo O3,and Mg6Al2(OH)16.Meanwhile,the other 2D layered materials,such as transition metal carbon/nitrogen compound(MXenes),borophene,and phosphorene,are reported one after the other.The emergence of phosphorene has unleashed tremendous interest in 2D group VA materials.In this thesis,focused on group VA2 D materials,based on first-principles calculations density functional theory(DFT),we have studied the structures and properties of phosphorene as well as the atomically thin binary group VA-VA compounds semiconductors.The contents and conclusions of the thesis are listed as follows:1.Using first-principles density functional theory calculations,we investigate the geometries,electronic structures,and thermodynamic stabilities of substitutionally doped phosphorene sheets with group IIIA,IVA,VA,and VIA elements.We find that the electronic properties of phosphorene are drastically modified by the number of valence electrons in dopant atoms.The dopants with an even number of valence electrons enable the doped phosphorenes to have a metallic feature,while the dopants with an odd number of valence electrons retain a semiconducting feature.This even–odd oscillating behavior is attributed to the peculiar bonding characteristics of phosphorene and the strong hybridization of sp orbitals between dopants and phosphorene.Furthermore,the calculated formation energies of various substitutional dopants in phosphorene show that such doped systems can be thermodynamically stable.These results propose an intriguing route to tune the transport properties of electronic and photoelectronic devices based on phosphorene.2.Searching the novel 2D semiconductor is crucial to develop the next-generation low-dimensional electronic device.Using first-principles calculations,we propose a class of unexplored binary VA-VA compound semiconductor(PN,As N,Sb N,As P,Sb P and Sb As)with monolayer black phosphorene(α)and blue phosphorene(β)structure.Our phonon spectra and room-temperature molecular dynamics(MD)calculations indicate that all compounds are very stable.Moreover,most of compounds are found to present a moderate energy gap in the visible frequency range,which can be tuned gradually by in-plane strain.Especially,α-phase VA-VA compounds have a direct gap while β-Sb N,As N,Sb P,and Sb As may be promising candidates of 2D solar cell materials due to a wide gap separating acoustic and optical phonon modes.Furthermore,vertical heterostructures can be also built using lattice matched α(β)-Sb N and phosphorene,and both vd W heterostructures are found to have intriguing direct band gap.The present investigation not only broads the scope of layered group VA semiconductors but also provides an unprecedented route for the potential applications of 2D VA-VA families in optoelectronic and nanoelectronic semiconductor devices.3.Finding novel 2D semiconductors is crucial to develop next-generation low-dimensional electronic devices.Using first-principles calculations,we propose a class of unexplored binary VA-VA compound semiconductors(PN,As N,Sb N,As P,Sb P and Sb As)with monolayer black phosphorene(α)and blue phosphorene(β)structures.Our phonon spectra and room-temperature molecular dynamics(MD)calculations indicate that all compounds are very stable.Moreover,most of compounds are found to present a moderate energy gap in the visible frequency range,which can be tuned gradually by in-plane strain.Especially,α-phase VA-VA compounds have a direct gap,while β-Sb N,As N,Sb P,and Sb As may be promising candidates for 2D solar cell materials due to a wide gap separating acoustic and optical phonon modes.Furthermore,vertical heterostructures can be also built using lattice matched α(β)-Sb N and phosphorene,and both vd W heterostructures are found to have intriguing direct band gaps.The present investigation not only broadens the scope of layered group V semiconductors but also provides an unprecedented route for the potential applications of 2D VA-VA families in optoelectronic and nanoelectronic semiconductor devices.4.Vertical integration of two-dimensional materials has recently emerged as an exciting method for the design of electronic and optoelectronic devices.In this letter,first principles calculations are employed to explore the structural and electronic properties of the Ge Se/phosphorene van der Waals(vd W)p-n heterostructure.Our results suggest that this heterostructure has an intrinsic type II band alignment and indirect band gap.Moreover,we also find that an intriguing indirect-direct and insulator-metal transition can be induced by strain.In addition,spontaneous electron-hole charge separation is expected to occur,implying that the Ge Se/phosphorene heterostructure is a good candidate for applications in optoelectronics.These results provide a route for applications of the Ge Se/phosphorene vd W heterostructure in future flexible electronics,optoelectronics,and semiconductor devices.