Synthesis, Doping And Optical Properties Of ZnO Semiconductor Nanocrystallines

ZnO is a new generationalm ultifunctional II-VI compound semiconductor with a wide and direct band gap. ZnO nanostructures show great promising applications in opto-electric devices surface acoustic wave devices, piezoelectricity materials, field emiters, sensors, ultraviolet Lasers, solar cells and so on.ZnO materials exhibit a wide range of electrical and optical properties that depend sensitively on both shape and size, and are of both fundamental and technological interest. We have demonstrated a simple vapor-phase approach to control growth of ZnO whiskers. Some types of ZnO whiskers with various shape and size, including ZnO nanowires,flower-like,urchin-like and comb-like nanostructures, have been obtained by controlled growth process in our laboratory. The micro morphology ,the phase composition and crystal structure of as prepared samples were analyzed by means of scanning electron microscope (SEM), transmission electron microscopy (TEM),X-ray diffraction(XRD),respectively. The growth mechanisms of various ZnO whiskers are proposed based on our experimental observations.The key for controlling the shape and size is the level of supersautration that controls ZnO nucleation and growth. The supersaturation in the reaction vessel strongly depends on the processing parameters. The formation of ZnO urchin-like nanowires follows a two-step process: one nucleation and another growth, it is found that the formation of the sphere-shaped liquid Zn droplets before adding oxygen is a key factor to control the morphology of the urchin-like nanowires; The formation of the comb-like microbelts follows the process: the microbelt is formed by a vapor-solid (VS) growth mechanism first, then the nanowires on one side are grown by a self-cataly growth parallel to the (0001) polar surface. Photoluminescence (PL) spectrum shows two typical emission peaks at ~390 nm and at ~495 nm were observed, which were assigned to UV emission and green emission, respectively.The micro morphology ,the phase composition and crystal structure of as prepared samples were analyzed by field emission scanning electron microscopy (FSEM)and energy dispersion spectroscopy (EDS). The result shows that Mg has influence on the morphology of ZnO nanostructures which may results from c-axis preferred growth, Mg can be doped into ZnO crystal latic.Different PL spectra are observed for MgxZn1-x0 nanostructures when excited by different wavelengths with the Xe lamp at RT. The wavelengths of the PL peaks are related to the excitation wavelength. The stronger peak is obtained in the blue band, while the weaker peak is obtained in the ultraviolet band. With the increase of the Mg contents, it is found that MgxZn1-x0 nanostructures prepared at different temperature show a slender blue shift of UV emission when the exciting wavelength is identical. Zn0 and MgxZn1-x0 nanostructures show bright excitonic luminescence in UV band. The blue and green peaks of one nanostructure depend on its defects.