Structural And Optical Properties Of ZnO Films Grown Under Various O₂/Ar Gas Ratios And Hydrogen-implanted ZnO Films

As the third generation of semiconductor, ZnO has many excellent characteristic for its wide direct bandgap (3.37 eV) and extremely large exciton binding energy (60 meV), thus can be applied to new blue and ultraviolet light emitting material. However, ZnO commonly is n-type conductive due to its native defects and hydrogen impurity, the achievement of p-type ZnO is rather difficult. The understanding of the relation between properties of ZnO thin films and growth condition (02/Ar ratio), and the introduction of different hydrogen concentration using advaced ion implantation technique, will contribute to studying influence of defects on their structural and optical properties. We have prepared ZnO thin films by radio frequency (RF) magnetron sputtering, using variable-energy positron beams (VEPAS) which are sensitive to vacancy-type defects, in combination with structural and optical measurements to characterize the transformation of defects or defect complexes in ZnO thin films under variable 02/Ar ratios R and ZnO thin films introduced by hydrogen before and after implantation. This has important significance on the comprehension of native defects in ZnO thin films and preparation of high stable and high qualitied ZnO thin films. Main contents and some new results are summaried as follows:1,Structural, and optical properties of ZnO films grown under various O2/Ar gas ratios. Thin wurtzite (002) textured ZnO thin films were deposited on glass substrates by RF magnetron sputtering under 02/Ar ratios R varying from 0.05 to 1.0 at room temperature. The structure of, and defects in, the films were investigated by XRD, SEM and VEPAS. The XRD spectra showed that ZnO thin films were polycrystalline with hexagonal structure and a good c-axis orientation perpendicular to the substrate. The thickness, grain size and the crystalline quality of the films strongly depended on R; the larger grain size and thicker ZnO films were grown when R was lower. Positron beam Doppler broadening measurements showed that in low R films additional vacancy-type defects (e.g. Zn-related vacancy complexes or clusters) were formed. Photoluminescence spectra found that the film with R= 0.4 had the highest luminescence efficiency, in good agreement with the best c-axis preferential orientation. The transmittance spectra of the films decreased with decreasing R, due to the thickness effect. Correlations between microstructure, defect and optical properties are discussed.2,Structural, and optical properties of hydrogen-implanted ZnO films. ZnO thin films were deposited on glass substrates by RF magnetron sputtering. Adjust O2/Ar ratios R to 0.4 and substrate temperature to 320℃. The (002) surfaces were implanted with 90 keV H+at doses of 1×1015 and 1×1016 H/cm2. The structural, and optical properties of the films were investigated by XRD, SEM, VEPAS, IR, PL and transmittance techniques. The experimental results indicate that, either unimplanted or hydrogen-implanted ZnO films have the similar infrared absorption spectroscopy. It has been suggested that the as-grown sample contains native hydrogen and forms O-H bonds, and more surface O-H bonds and H-I complexes are formed in ZnO thin films after H ion implantation, leading to the increase of IR peak intensity. The VEPAS result indicates that VZn-OH bond complexes are effective positron trapping centers, which induces an increase of S parameter. The XRD, SEM and PL results implies that they can behave as a shallow donor to decrease PL luminescence efficiency and crystallinity, increase the n-type conductivity and the transmittance of ZnO thin films.In addition, the content of this dissertation also contains the work of first-principles calculations on the structural, electronic and optical properties of a complex system where the 0.4 nm carbon nanotubes are confined inside the AlPO4-5 zeolite (AFI) channels. The interaction between the tube and AFI is described within the framework of local density approximation (LDA). Our results indicate that the AFI zeolite cannot be simply regarded as an inert template, and it has real effect on the physical properties of the carbon nanotubes grown inside.