ZnO Nanocrystals Hydrothermal Growth And Its Ultraviolet Optoelectrical Regulation

ZnO is a low cost and environmentally friendly semiconductor with a wide direct bandgap(3.37eV) and a large exciton binding energy (60meV) at room temperature, which makes it apromising material for applications in light emitting diodes(LEDs), ultraviolet photodetectors, solarcells, transparent conductive oxide(TCO), field-effect transistors(FETs), sensors, spintronics and soon. Recently, the bandgap engineering of ZnO has been a top theme in the academic field.Thebandgap broadening of ZnO nanomaterials can be achieved by doping particular elements, having avery important application in the ultraviolet photodetectors.In this paper, high-temperature-mixing hydrothermal (HTMH) synthesis of ZnO and Mg-dopedZnO nanocrystals was performed. During the preparation, the magnesium nitrate provides dopant ions,zinc nitrate as raw material, deionized water as the solvent. The obtained samples were characterizedby XRD, SEM, TEM, UV-Vis and fluorescence spectrophotometer. The effects of hydrothermalconditions on structure, morphology, optical properties of ZnO nanocrystals were investigated. Weexplored the band gap varying with the Mg components of doped ZnO nanocrystals obtained with theabove non-doped ZnO optical process parameters.The experimental results showed that highly crystalline ZnO nanocrystals with uniform sphericalmorphology fabricated by HTMH can be formed at alkali concentration and temperature windows aswide as0.1~0.5M and160~200oC, respectively. It was found that surfactants are favor of the ZnOnanorods formation. ZnO photoluminescence spectra contain only near385nm UV emissionoriginating from the near-band-edge(NBE) under different alkalinity, mixing temperature, surfactantconditions.The optimal conditions of ZnO nanocrystals preparation were200℃and0.1mol·L-1.The preparation of MgxZn1-xO by HTMH, Mg(OH)2impurity phase segregated at x≥0.6,where xis the value of Mg/(Mg+Zn). The bandgap can be achieved between3.23and3.39eV with theincreasing of x. There is no segregated impurity phase at x≤0.5.MgxZn1-xO photoluminescence spectra contain only near UV emission originating from thenear-band-edge (NBE) at x≤0.5, which is agree well with the optical bandgap, implying the goodquality of doped nanocrystals in HTMH.In addition, we also try to probe the effects of subsequent UV treatment for highly transparentconductive ZnO films.