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Characterization for the Structures and Properties of Wide Bandgap Semiconductor In2O3 by First-principle Calculations

Author: SunHongGang
Tutor: ZhaoXian
School: Shandong University
Course: Materials Science
Keywords: In2O3 Optical Properties Semiconductor Photocatalytic Doping Intrinsic defects CASTEP DMol ~ 3 Density functional theory
CLC: O471
Type: Master's thesis
Year: 2009
Downloads: 364
Quote: 1
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Abstract


In recent years, the wide band gap semiconductor matrix material due to its unique physical and chemical properties, making it the field of electronics, chemistry, physics and biology shows the huge potential of the formation of these materials had an active area of ??research. The new features in the experiment was prepared with the excellent performance of the new materials and the development of existing materials is the direction of the efforts of the scientists. On the theoretical side, the quantitative workers committed Quantification Theory based on the use of computer simulation technology, and theoretical study of the electronic structure and optical properties of semiconductor to explore the nature of the semiconductor optoelectronic performance. In this paper, based on first-principles calculation under the framework of the density functional theory, analysis of the the wide forbidden the semiconducting In 2 O 3 of the intrinsic nature of, and to further explore the doped Miscellaneous and defect states in the the In 2 O 3 electronic structure and optical properties of impact. The main contents are as follows: First-principles study pure In 2 O 3 geometry and optical properties. The use of the the CASTEP module, Material Studio software In 2 O 3 of geometry, electronic structure and optical properties of the cubic phase and rhombohedral. The imaginary part of the dielectric function of the optical properties can be calculated by the electronic structure directly, the real part of the dielectric function, Kramer-Kronig dispersion relations. The optical properties of other optical constants such as refractive index, reflectivity and absorption coefficient can be obtained through the dielectric function. The display of the electronic structure and the population analysis, In and O bonding between main function is an ionic bond, but there are still a small amount of covalent components. According to the band density of states, we analyze and determine embodied in the imaginary part of the dielectric function of light absorption and transition corresponds to In 5s states of the conduction band bottom electronic transitions from the valence band O 2p state to its peak in 6eV nearby ; in 9eV nearby peak corresponds to the conduction band In 5s or 5p-state electronic transitions from the valence band O 2p states. Crystal weak absorption in the visible region of 0 ~ 5eV Description In 2 O 3 is a good transparent material. Calculated in good agreement with the experimental results, the study of these properties of great reference value for the In 2 O 3 application. Density functional theory calculations and analysis of N-doped and N: H codoped In 2 O 3 geometry and photocatalytic properties. (A) We construct the N gap and replace doped In 2 O 3 model based on the density functional theory DMol 3 Software N-doped In 2 O 3 geometry and band structure. The calculation results show that the N impurity doping in the form of electronic structure. As can be seen from the diagram of the energy bands and the density of states: replace doping N 2p impurities-state of the formation of impurity states in the valence band above the top of the photoexcited state to the transition between the bottom of conduction band electrons from the N 2p impurities, resulting in doped material absorption edge redshifts; the the gap doping N 0 - structure present in the band gap of the energy band structure of two NO π orbitals (anti-πorbitals) form N0 , mainly contributed by impurities N 2p states. In addition, due to the cubic phase and rhombohedral an In 2 O 3 electron density different, leading to different crystalline phases in the N-doped In 2 O 3 band structure change is different, the cubic phase band the change than rhombohedral's much weaker. (B) In order to understand the role of H atoms in the N doping, we build the N: H co-doped cubic phase In 2 O 3 model, using the first The principle of calculation of the comparative analysis of the pure, N-doped and N: H codoped energy band and density of states changes. The calculation results show that In NH Codoped, the H from the donor role, providing electronic. Replace doping can reduce the energy of the N 2p states, so that the valence band O 2p hybrid, and thereby improve the energy band structure. Doped in the gap to reduce the number of band gap impurity level, so that the band gap of NO anti only a π orbital, and the band gap reduces. Overall, the role of H is the role of the impurity level decreased, and the valence band hybrid enhanced. 3 first-principles calculation and analysis of the cubic phase In 2 O 3 intrinsic defects. Density functional theory we analyze the nature of the in cubic In 2 O 3 in this configuration of the intrinsic defects, the formation energy and electronic structure. Formation energy calculation showed that oxygen vacancies both in excess oxygen or oxygen-depleted conditions, are the most easily formed, while remaining stable, defect structure and the partial pressure of oxygen. Oxygen vacancy causes electrons occupy an energy level in the bottom of the conduction band, forming a donor level Fermi level to move to the bottom of the conduction band. Because of its low formation energy, so it is to make the In 2 O 3 be the main factor of the n-type conductivity material; gap for oxygen to reach a steady state, in the optimization of the configuration After forming a the peroxy structure O 2 2 - , caused by the band gap decreased significantly, and occupied by two anti-π level above the top of the valence band. Indium vacancy has little effect on the electronic structure of the acceptor level near the top of the valence band is of a p-type conductivity defects, but because of its higher formation energy, does not show up in the crystal conductive; indium gap formation two donor levels shallow donor level through the Fermi level occupied by a single electron deep donor level is located below the Fermi level is two single electrons occupy. The calculation results show that, in the variety of the intrinsic defects, oxygen gap can well improve the the In 2 O 3 of light absorption, to increase its photocatalytic activity. From the point of view of literature research, In 2 O 3 research is based on the experimental preparation, the theoretical study of its nature especially its photocatalytic performance studies also very little. Start from the electronic structure, combined with the geometric structure of Mulliken charge population and the analysis of the optical absorption spectrum of N, NH, and the intrinsic defects of In 2 O 3 optical performance the impact of a more reasonable explanation. While we study the use of the principle of Solid State Physics, on the other hand combined with some theoretical chemistry, new progress in this study, In 2 O 3 have a better understanding of the nature of the material.

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