Sol-gel Method Synthesis and Characterization of ZnO Nanoparticles for the use in Optoelectronic Devices

Abstract

The precursors used in the preparation were zinc hexahydrate, sodium hydroxide, and methanol (as it is without purification). Citric acid was added during preparation for the sake of molecule disperser purpose and surface modification. ZnO nanoparticles have been successfully synthesized by the sol gel method. The main motivation for this thesis is not only to successfully realize the controllable synthesis of ZnO nanoparticles, but also to investigate the structure, optical and electrical properties in detail by means of scanning electron microscopy (SEM),transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy and X-ray diffraction (XRD) and UV-Vis absorbance in the ZnO nanoparticle is demonstrated. The effect of annealing temperatures on the morphology, optical and electrical properties of the nanoparticles were also systematically studied. Different techniques are used to investigate the performance of ZnO nanoparticles use in optoelectronic devices such as light emitting diodes, laser diodes, and photoconductivity. X- ray diffraction (XRD) indicated that all the grown ZnO nanoparticles produced was crystallize in the wurtzite structure and post growth annealing does not significantly enhance the crystalline quality of the material. The effect of annealing temperatures on the morphology of grown ZnO nano particles was examined by using scanning electron microscope (SEM) and transmission electron microscope (TEM). The optical quality of ZnO nanoparticle was carefully examined using photoluminescence (PL). The PL analysis showed that the nanoparticles have the same characteristics as that of bulk ZnO, except for the stronger contribution from surface related bound excitons in the former case. Surface adsorbed impurities causing depletion and band bending in the near surface region is implied from both UV and PL. Regardless of the annealing environment, annealing at a temperature as low as 300C enhances the UV emission and suppresses defect related deep level emission. However, annealing above 500C is required to out-diffuse hydrogen presence, which is in the low temperature PL spectra of ZnO.