| Zinc oxide (ZnO) is a wide band gap semiconductor material. It is a promising candidate for short wavelength optoelectronic devices.; Single crystalline and nanocrystalline ZnO thin films have been grown by organo-metallic chemical vapor depositions in a pulsed organo-metallic beam epitaxy (POMBE) system. The structural and morphological properties of ZnO films strongly depend on growth conditions. For epitaxially grown ZnO films on sapphire under optimal conditions, excellent crystallinity have been confirmed by X-ray diffraction (XRD) and high resolution transmission electron microscopy (TEM) studies. Nanocrystalline films with columnar-shaped grains are grown with different grain sizes. With decreasing growth temperature, the morphology of POMBE grown ZnO goes through an transition from continuous thin film to nanorods.; Well-aligned ZnO nanorods have been grown using two-step chemical vapor deposition methods. The growth mechanism is based on studies of ZnO nucleation. By controlling substrate temperature and oxygen concentration during the nucleation and growth steps, ZnO nanorods growth is achieved without any catalysts. High-resolution TEM studies show that ZnO nanorods are single crystals. Alignment of these nanorods depends on lattice match between ZnO and substrate. ZnO nanorods with different areal densities can be obtained by varying nucleation time. The photoluminescence (PL) spectra of nonorods have shown band edge emission at 380 nm with full width at half maximum (FWHM) of 106 meV which is comparable to films grown by molecular beam epitaxy (MBE). Green emissions are found to originate from oxygen vacancies and zinc interstitials; while orange-red emissions are attributed to oxygen interstitials.; Optical properties of ZnO thin films and nanostructures are studied. Clear excitonic features observed in different optical measurements have proven good optical qualities of single crystal ZnO films. By alloying with magnesium, band gap of ZnO can be widened. "Random lasing" phenomena are found in ZnO nanocrystalline films. Resonant cavities in random laser are recurrent light loops formed by multiple scattering. The lasing threshold strongly depends on structural properties of the media, such as grain sizes and excitation areas. Ultraviolet ZnO microdisk laser are fabricated on SiO 2/Si wafer to achieve lasing in whispering gallery modes (WGM). |
