Study On Electronic And Optical Properties Of M/LaAlO₃ Bilayer Thin Films

In recent years,two-dimensional(2D)materials,including graphene,transition metal sulfides,and boron nitride,have made significant research progresses.2D material,which is a kind of surface structure material,or called layered structure material.When the binding force is very small in a certain direction,the material can be simply made into a layered structure by external force to form a 2D material.Nobel Prize winner Kroemer once pointed out that the interface is the device.Actually,the working areas of 3D devices are also in the contact of 2D interface,such as PN junctions,information memories,various sensors.Therefore,the construction of heterostructure interfaces with 3D materials is of great significance to the research and innovation of devices.However,the application of a single 2D material has some serious limitations,and they are also severely restricted by the weakly interacting electrons of s and p orbitals.Therefore,researchers have begun to focus on two aspects of research.On one hand,they continue to search for emerging 2D materials by advanced synthesis methods and techniques,more 2D materials can be prepared on a large scale.On the other hand,two separate 2D materials can be connected to each other by van der Waals force between the layers to achieve the effect of one plus one greater than two.The classic three-dimensional heterostructures have brought researchers huge and novel research results.However,due to the lattice mismatch,it is difficult for a heterojunction to be formed.Van der Waals heterostructures can be a perfect solution to solve this problem for new electronic devices.Therefore,the study of exploring and developing new types of heterostructures is extremely important.This work is based on density functional theory for first-principles calculations and calculated by the VASP package.This paper focuses on modulating the electronic,optical and elastic properties of classical metal oxide perovskite as a 2D materials and corresponding heterostructures.The main contents of this thesis include optimization of structural parameters,confirmation of heterojunction stability,calculations of band structure,dielectric function,and elastic modulus,etc.,which provide theoretical support for exploring and designing new optoelectronic devices.The details are as follows:1.We calculated the stability,lattice constant,band structure diagram,electronic density of state,dielectric function and elastic modulus of metal oxide perovskite LaAlO₃ and SrTiO₃ monolayer structures and their heterostructures.The research results show that when a STO monolayer and a LAO monolayer form a heterojunction,the band structure converts from an indirect bandgap to a direct bandgap,and exhibits a type-I band alignment.Electrons and holes are restricted in a small range of energy,which helps improve the performance in LED devices.In addition,the influence of biaxial strain on the electronic,optical and elastic properties of 2D SrTiO₃/LaAlO₃heterostructures was studied,and we found that biaxial strains can effectively adjust the electronic and optical properties.And the formation of heterojunction can effectively improve the material's performance to provide powerful guarantee for its practical application.2.The structure and electronic properties of bilayer LaAlO₃(111)(LAO111)and monolayer WS₂ are studied by first-principles calculations.The negligible lattice mismatch makes the heterostructures easier and more stable to be formed.Based on this,different stacking models are considered,and the most stable structure can be found and studied in accordance with the formation energy.Focusing on the projected band structure,the electronic density of states,the energy band arrangement and the optical properties of the heterostructure under different biaxial strains,the research results show indicate that the 2D WS₂/LAO111 heterostructure has an indirect band gap of type-? band alignment,which indicates the effective realization of the space separation of electrons and holes,and provides possibilities for its application in high-efficiency solar cells and solar water splitting.