| For several decades, the preparation, characteristics and application of the wide band gap semiconductor oxide materials have attracted more and more attention in many fields. Among them, tin oxide and transition metal doping has have received increasing interest in photovoltaic devices, gas sensors, oxide dilute magnetic semiconductor, transparent electrodes. Optical characterization is a powerful non-destructive detection technology, through which we can obtain the optical constants, lattice vibration, energy band structure, photoluminescence, electronic transitions and other important information for the material. They are closely related to the chemical composition, crystalline quality, impurity level and defects of the material. Unfortunately, no more studies on the optical properties of transition metal (TM) doped SnO2films in a wider photon energy region, especially for optical functions and TM doping effects, have been systematically presented up to now. Therefore, it is necessary to explore the relationship of temperature and preparation conditions (such as the doping level, substrate temperature, oxygen atmosphere) on the optical properties for SnO2semiconductor oxide film material, then provide scientific basis for its application in the field of energy, spinelectronic and optoelectronic devices. The main works of this dissertation are listed as follows:1. The optical functions, infrared active phonon modes, and photoluminescence emission bands of Sn1-xMnxO2(0≤x≤0.15) films on c-plane sapphire substrates in the far-infrared-ultraviolet photon energy range have been studied. The theoretical models are applied to reproduce the experimental transmittance and reflectance spectra well. The effects from the Mn doping on the optical properties have been discussed in detail.Optical properties of Sn1-xMnxO2(x from0.0to0.15) nanocrystalline films grown on c-plane sapphire substrates have been investigated at room temperature by ultraviolet-infrared transmittance, far-infrared reflectance, and photoluminescence spectra. The X-ray diffraction analysis indicate that the films are of tetragonal rutile structure without any Mn compounds,except for5%Mn doping, in which the slight orthorhombic phase appears due to the presence of defects and strain. The dielectric functions are successfully determined from0.025to6.5eV using the Adachi and Lorentz multi-oscillator dispersion models in the high and low photon energy regions, respectively. The fundamental absorption edge is found to shift toward a lower energy side with increasing Mn composition. The refractive index of pure SnO2film is estimated to be the lowest among the Sn1-xMnxO2system. On the other hand, the low Eu transverse optical (TO) phonon frequencies slightly increase with the Mn composition. However, the highestî–›(TO) and A2u(TO) vibration modes present an opposite change trend. Compared with SnO2single crystal, four corresponding longitudinal optical (LO) phonon frequencies decrease for the films owing to the variation of the lattice constants and destruction of the crystal symmetry. Photoluminescence spectra of doped SnO2films show the remarkable intensity changes and a blue-shift trend compared to pure SnO2film. Moreover, a novel emission peak of about1.56eV associated with the Mn dopant can be observed. It can be concluded that the Mn incorporation effects are the main contributions of different optical response, because the replacement of Sn with Mn ion can induce the2p-3d hybridization and result in the electronic band structure modification of the Sn1-xMnx02films.2. Microstructure, Raman scattering, transmittance, reflectance and PL emission measurements of Sn1-xFexO2(0≤x≤0.2) films on c-sapphire substrates have been investigated. The dielectric functions in the far-infrared-ultraviolet photon energy region are extracted by reproducing the experimental spectra with reasonable optical dispersion models. The magnetic composition and temperature effects on the electronic structure, phonon modes, optical band gap, and the excitonic transition features have been discussed in detail.Nanocrystalline iron-doped tin dioxide (Sn1-xFexO2) films with x from0to0.2were prepared on c-sapphire substrates by pulsed laser deposition. X-ray diffraction and Raman scattering analysis show that the films are of the rutile structure at low compositions and an impurity phase related to Fe2O3appears until the x is up to0.2, suggesting the general change of lattice structure due to the Fe ion substitution. The dielectric functions are successfully determined from0.0248to6.5eV using the Lorentz multi-oscillator and Tauc-Lorentz dispersion models in the low and high photon energy regions, respectively. With increasing Fe composition, the highest-frequency transverse optical phonons Eu shifts towards a lower energy side and can be well described by (608-178x) cm-1. From the transmittance spectra, the fundamental absorption edge is found to be decreased with the Fe composition due to the joint contributions from SnO2and Fe2O3. It can be observed that the doped films exhibit evident excitonic excitation features, which are strongly related to the Fe doping. Three electronic transitions can be uniquely assigned. Among them, the6A1gâ†'4T2g transition contributes to the onset of optical absorption. The variation law between electronic transitions and temperature for the20%Fe doped film has been established. Moreover, the remarkable intensity reduction and a red-shift trend with the doping composition, except for the pure film, can be testified by the photoluminescence spectra. One can further find that the room temperature photoluminescence properties strongly depend on the oxygen vacancies, oxygen defects, and doping concentration.3. Comprehensive characterizations are performed to explore the morphology, crystallinity, and the chemical states of the TM (Mn or Fe) doped SnO2films with the compositions of5%(Sn0.95TM0.05O2) prepared under varied Po values. We demonstrate the crucial role of surrounding oxygen on electronic band structures and optical properties by means of infrared reflectance, ultraviolet-near-infrared transmittance, and photoluminescence spectra. The comparative study on the Sno.95Mn0.05O2and Sno.95Feo.05O2films will be presented and oxygen vacancy contribution associated with the3d dopants will be discussed in detail.Transition metal (TM:Mn or Fe) doped tin dioxide (SnO2) films with the compositions of5%(Sn0.95TM0.05O2) have been deposited on sapphire substrates by pulsed laser deposition under oxygen pressure (Po) varied from10-4to1Pa. The X-ray diffraction, scanning electron micros-copy, and infrared spectra analysis show that different TM dopants can affect the variations of crystallization and lattice distortion. Moreover, x-ray photoelectron spectroscopies indicate that the effective Po during the growth does not change the valence state of Sn4+in the Sno.95TM0.05O2films. The spectral behaviors of the films have been investigated in the photon energy range of0.47-6.5eV (2650-190nm). From transmittance spectra, the shoulder structures become more prominent for the Sno.95Fe0.05O2film than those for the Sno.95Mn0.05O2film due to the Fe repelling effect of much stronger p-d hybridization. The refractive index values for the Sn0.95Mno.05O2film are found to be larger than those for the Sn0.95Fe0.05O2film at the photon energy of0.47eV. The main peaks at about1.9and2.2eV in photoluminescence emission spectra for both Sn0.9sMno.o502and Sno.95Fe0.05O2films can be observed, and it could be explained by the fact that the electrons in the conduction band of SnO2relax to defect states and then radiatively recombine with the holes. From direct comparison of PL and transmittance results for the films, the electronic transition energies, the emission peaks’ intensities and positions are shown to present the Po dependent behavior. The distinct trends indicate that the incorporation of Mn and Fe elements can provide a significant difference in the crystalline and electronic band structure. It can be concluded that the oxygen pressure and dopant contributions are responsible for the adjustment of electronic band structures and result in different optical response behaviors for the Sn0.95TM0.05O2films.4. Cuprous oxide (Cu2O) films have been prepared by sol-gel method. The Raman vibration and transmission as a function of temperature have been observed.Anomalous low temperature behaviors in CU2O film grown on quartz substrate have been investigated by temperature-dependent Raman and transmittance spectra. The longitudinal optical components of two Γ15-phonon modes become sharper and more intense at a low temperature. Five electron transitions can be observed and uniquely distinguished in the transmittance. It can be found that the highest-order electronic transition located at6.4eV exhibits a minimum transmittance near200K. Correspondingly, the variations from phonon intensity ratios reveal obvious anomalies with the decreasing temperature, indicating the existence of strong electron-phonon coupling mediated by Frohlich interaction in the CU2O films below the temperature of... |
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