Theoretical Design And Performance Study Of Several Tellurium-based One-dimensional Semiconductor Materials

Exfoliation of two-dimensional materials into mono-or few-layer sheets has attracted humongous interest in exploring low-dimensional materials.The concept of layered materials can be extended from two-dimensional materials with weak bonds in one direction to one-dimensional materials with weak bonds in two directions.One-dimensional weak bond materials have an atomic-scale thickness and excellent physical properties.Among many weak bond materials,tellurium is a valuable narrow band gap material that can be exfoliated.Tellurium compounds have unique electrical,optical and mechanical properties.Inspired by the successful stripping of one-dimensional tellurium chains,this project studied the one-dimensional chain structures of three subhalogenated tellurium compounds Te₂Br,Te₂I,and Te₃Cl₂.These telluride crystals are formed by stacking multiple van der Waals chain structures.They can be stripped into one-dimensional single-chain or few-chain structures without destroying the integrity of the crystal.In this paper,through first-principles calculations,the structure,electrical and optical properties of the exfoliated one-dimensional chain are studied.The introduction part of this thesis introduces the research progress of low-dimensional nanomaterials,especially one-dimensional chain crystal materials in one-dimensional nanomaterials.In the second chapter,the theoretical knowledge and calculation methods used in the research of the subject are introduced.Then in Chapter 3 to Chapter 5,the theoretically predicted one-dimensional single-chain and few-chain structures separated from weakly bonded solids Te₂Br,Te₂I and Te₃Cl₂are introduced.The specific content is as follows:(1)Designed one-dimensional single-chain and few-chain structures separated from bulk Te₂Br.The one-dimensional Te₂Br structure has lower peeling energy,indicating that single-chain or less-chain systems can be prepared from bulk.The one-dimensional single-chain Te₂Br structure is a stable direct band gap semiconductor with a band gap value of 1.78 e V.One-dimensional single-chain Te₂Br has good structural flexibility,and the structure can withstand 25%tensile strain or 15^°twisting strain.In addition,we study the structure and energy band properties of one-dimensional double-chain,triple-chain,and quadruple-chain Te₂Br.The energy band results show that as the number of chains increases,the band gap value gradually decreases.The transition from the indirect band gap of the bulk structure to the direct band gap of the one-dimensional structure indicates that the system has a strong quantum confinement effect.These one-dimensional chain Te₂Br structures have moderate band gaps,good mechanical properties,excellent electron mobility and significant light response in the visible light range,making the one-dimensional chain Te₂Br structures have potential applications in flexible electronic and optoelectronic devices.(2)Bulk Te₂I is a quasi-one-dimensional crystal with van der Waals inter-chain interactions,which exhibits direct band gap properties.The binding energy,phonon spectrum and molecular dynamics of the one-dimensional single-chain Te₂I structure separated from the bulk phase confirm that the structure has good stability.One-dimensional single-chain Te₂I is an indirect band gap semiconductor with a band gap of 1.51 e V,which is close to the ideal band gap for solar absorption.When an external electric field is applied,the one-dimensional single-chain Te₂I keeps the indirect band gap unchanged and the band gap value can be adjusted.The absorption spectrum of one-dimensional single-stranded Te₂I shows that it has a good light-trapping ability in the ultraviolet region.In addition,the four one-dimensional few-chain Te₂I structures exhibit the same indirect band gap properties.The band gap value increases with the decrease of the number of chains,indicating that there is a strong quantum confinement effect in the Te₂I system.These results indicate that the one-dimensional chain Te₂I can be used as a candidate material in the field of optoelectronics.(3)In the third work,we study the one-dimensional single-chain Te₃Cl₂ structure,which is a wide indirect band gap semiconductor with a band gap of 2.49 e V.The separation energy of one-dimensional single-chain Te₃Cl₂ from the bulk phase is 115.2 me V/atom,which is much lower than that of one-dimensional tellurium chain.Through binding energy,phonon spectroscopy,molecular dynamics and other methods,it is verified that the one-dimensional Te₃Cl₂ chain structure has good stability.The energy band change of the structure was explored by applying an external electric field to the structure.These results show that under the control of 0.2-0.8 e V/(?)electric field,with the increase of electric field intensity,the band gap value gradually decreases.At0.8 e V/(?),the band gap value is reduced to 1.45 e V,indicating that the electric field can effectively regulate the energy band of the one-dimensional Te₃Cl₂ structure.In addition,it exhibits good light absorption in the ultraviolet region.These results show the application potential of one-dimensional Te₃Cl₂ structure in the field of new optoelectronic devices.