The Effect Of Octahedral Torsion On The Metal Insulator Transition In The Perovskite Iridium Oxide Film

Because the progress of traditional silicon semiconductor technology,the electron component with silicon as it's foundation is gradually approaching the horizon of its operation and storage speed.By contrast,metal oxides are expected to be the cornerstone of the next generation of electronic industrial revolution,witch with more degrees of freedom.The metal-insulator transition is one of the unfading research fields in the transition metal oxide system.While the implement method of the metal-insulator transition includes bandwidth control and band filling,the theory includes mott transformation,Slater transformation and other models based on strong correlation interactions.But with the extension of sample preparation methods and research materials,there were many electronic transportion behaviors that cannot be explanated by strong relevance theory were discovored such as two-dimensional electron gas modulated by interface states in LaA1O₃/SrTiO₃ interface and insulative ground state resulted by spin orbit coupling effects in iridium oxide.The purpose of this paper is to use traditional and new methods to explore metal-insulator transition in non-strong correlation system.So we studied the modulating effect of interface roughness,doping electron concentration and the concentration of oxygen vacancy on the metal-insulator transition in TiO₂ order/disorder homojunction.And we successfully changed temperature of metal-insulator transition in 5d electronic material CaIrO₃ thin film through the extension stress.This thesis consists of six chapters:Chapter 1 We first introduce the knowledge about the origin and control method of two-dimensional electron gas,including ohm contact,band bending,interface polarity,schottky barrier,oxygen vacancy concentration,charge transfer,the properties and related applications of TiO₂.And then we introduces the knowledge about the regulation effect of the spin orbit coupling interaction and crystal structure distortion on metal-insulator transition in 5d metal oxide,including the band structure of the iridium oxide and the effect of the broken symmetry on the band structure,and the lattice structure,transport behavior and the origin of insulating ground state of the common iridium oxide.In the end,we introduce the knowledge of the epitaxial stress and octahedral distortion in the film growth process.Chapter 2 This chapter mainly introduces the growth process and method of perovskite metal oxide film,as well as the representational means of morphology characterization and the measurement of transport behavior,which include the preparation of polycrystalline target material,the use of pulsed laser deposition system,the working principle of atomic force microscope,XRD measurement of single crystal film thickness and reciprocal space,the use of low temperature measurement system and so on.Chapter 3 In this chapter,we control the metal-insulator transition temperature of homogeneous junctions in a wide range by controlling the three variables.Including changing the flatness of the interface by using ratio of monocrystalline and disordered layer thickness;changing the electron concentration with the impurity concentration;changing the oxygen vacancy concentration by oxygen pressure.It is concluded that the oxygen vacancies are the source of the interface carriers and the interface provides the conductive channel,and the flatness of the interface has an impact on the mobility.Chapter 4 we realize the notably regulation of the metal-insulator transition temperature in the CaIrO₃ thin film and conclude that the CaIrO₃ thin film own two different conductive mechanism by changing the kind of the substrate and the film thickness.And we claim that octahedral torsion is the main factor to adjust the bandwidth by measuring the corresponding lattice constant and torsional Angle.After that,we also found the anisotropy of metal insulation transition temperature in CaIrO₃ thin film and proposed the origin of the anisotropic conductive are the specific direction distribution of the degenerate band energy point near the Fermi surface in the Brillouin zone and the nonuniform lift of the band gap.