Epitaxy Growth And Electronic State Tailoring Of Inorganic Semiconductor Materials

Chemistry is a natural science to study the composition,structure and variation of substance.Because the substance is build up of atoms,the microstructure of atomic arrangement within substance determines its macroscopic properties.Chemistry is also an experimental science to creat new substance and metarials.Properties of lattice,orbit,charge and spin in materials are the key factors affecting their microstructure.Under the combined action of these factors,the electronic structure of each material is formed and endows the material with rich physical and chemical properties.Therefore,the creation of new materials heavily depends on tailoring of electronic state.Chemical reaction,the breaking and bonding process at the atomic level,is an available method to tailor electronic states with high accuracy.Besides chemical reaction,creation of solid materials needs “assembly” or crystallization.Exactly,epitaxy growth is the method for “assembly” or manipulation of microscopic particles(atom and molecule)with regular arrangement.It can be used to fabricate crystalline materials with high controllability.So the combination of chemical reaction and epitaxial preparation will be the perfect combination of directional synthesis and precise control.This will have incomparable advantages in the creation of new materials and new substances.Inorganic semiconductor material is the star material to solve the current energy and environmental crisis.Though great progress has be achieved over past years,there are still many problems to be solved.Herein,we select inorganic semiconductor material as the research object.With intensive study on the regulation of electronic states tailoring in the epitaxial growth,we try to provide new research ideas and experimental methods for creation of new substances and materials.The research begins with understanding the epitaxial growth of inorganic semiconductors.Then,a new material based on simple semiconductor is proposed and fabricated with epitaxial growth technique.Finally,the combination of chemical control and epitaxial growth is extended to the complex oxide semiconductor system.The following results are obtained:1.The problem of lattice mismatch in epitaxial growth was solved by surface chemical modification of the substrate.In the growth of GaSb on Si(111)substrates by molecular beam epitaxy,the in-situ monitoring of the growth process was carried out by the reflection high energy electron diffraction instrument.We found that the growth mode of GaSb thin films can be changed by adjusting the arrangement of atoms on the surface of silicon substrate.GaSb thin films adopted the island growth mode on the original Si(111)-(7 ? 7)the surface.This is mainly because the lattice mismatch between Si and GaSb is as high as 12% and the lattice mismatch stress can be effectively released by formation of misfit dislocations at the epitaxial interface.It was confirmed by TEM that there really existed periodic misfit dislocations at the interface.So the crystallinity and surface roughness of the samples needed to be improved.However,the epi-growth of GaSb films on Si(111)-(?3 ? ?3)-Sb and Si(111)-(5?3 ? 5?3)-Sb surface deviated from the normal crystal orientation.Due to the formation of coincidence site lattice,the lattice mismatch stress was released and the edge dislocation was eliminated completely.Correspondingly,crystal quality and surface morphology of the films were improved.But,the crystal quality of the latter was better for its in-plane matching lattice with a higher density at the epitaxial interface.With the perspective of synthetic chemistry,this part of the work solved the problem of lattice mismatch in epitaxial growth.It will have a certain reference value for the epitaxial growth of large lattice mismatched materials.2.Liquid droplet epitaxy was used to fabricate the Ga-GaSb metal-semiconductor heterostructures and their optical absorption properties were tuned.The droplets of low melting point metal Ga were chemically treatmented with Sb in molecular beam epitaxy and Ga-GaSb metal semiconductor heterostructures with specific size and composition were synthesized.Through the analysis of the composition,morphology,phase diagram,the droplet epitaxial growth mechanism from metal to heterojunction product was proposed.When the solid absorption spectra of samples were tested,it was found that the optical absorption properties of the samples were better in the lower size of the heterojunction and the lower proportion of semiconductor.This was mainly because Schottky barrier formed at the interface between metal and semiconductor could effectively accelerate the electron in conduction band to transfer into the Fermi level of metal.Then exciton density was reduced in the system and this could reduce the recombination probability.So,more carriers could be excited.With the valence band spectra data,it was confirmed that there existed charge transfer between the compositions.This part of the work makes full use of the accuracy of epitaxial growth in synthetic chemistry and invents new method for preparing metal-semiconductor heterojunction.And it also provides new ideas about the creation of new materials and the discovery of new matter state.3.For oxygen evolution reaction(OER),the catalytic activity of LaFeO3 films was promoted by oxygen vacancies.Pulsed laser deposition was used to fabricate the single crystal films of LaFeO3 and the in-situ annealing treatment was carried out in vacuum to introduce oxygen vacancies.The average valence of Fe in the vicinity of the surface was reduced.Oxygen vacancies could cause the electronic doping effect and the top valence band moved forward the Fermi level.This meant a higher conductivity.At the same time,the reduction of the valence state of Fe also made the Fe-O bond become longer.This lattice expansion caused the optical band gap narrowing.The spectral response range was extended,so as to enhance the catalytic current of OER.In addition,because the oxygen vacancies existed only in the vicinity of the surface,the valence band shift from bulk to surface could lead to the formation of bulk-surface heterojunction.It would accelerate the kinetics of OER and decrease the overpotential.In this part,the effective combination of epitaxial growth and chemical control is realized.That is to say this method can be used to create more new complex materialsBy studying the relationship between the structure and properties of materials,this paper explores the experimental methods to control the properties of materials.By creatively combining the functional orientation of chemical synthesis with the precise controllability of epitaxial preparation,the scientific connotation of synthesis and preparation is enriched in this process.This offers a new perspective for the development of solid state chemistry.It also provides a new experimental method for the creation of new materials and the discovery of new matter state.