Seed layers for the growth of oriented vertical arrays of ZnO nanorods

Conference Dates

October 1-6, 2017


ZnO is a direct wide bandgap semiconductor crystallizing in the wurtzite structure with a series of unique properties: a large exciton binding energy; good optical transmittance in the visible region; high optical gain; piezoelectricity; room temperature ferromagnetism; mechanical stability given by the high melting point and large cohesive energy; radiation hardness; or biological compatibility. These properties allow for applications of ZnO in UV light-emitting devices and detectors, field-effect transistors, solar cells, piezoelectric nanogenerators, or chemical sensors. For the majority of these applications, upright standing arrays with controlled positioning, sizes, and physical properties are preferred.

Chemical bath deposition (CBD) is a low-cost, low-temperature, surface scalable technique to grow ZnO nanostructures on virtually any substrate with a suitable seed layer. We show how the properties of the seed layer such as the texture, roughness, and porosity affect the nucleation and the alignment of ZnO nanorods (fig. 1a,b). The ZnO seed layers were prepared by electrophoretic deposition of a commercially available solution of ZnO nanoparticles dispersed in ethanol and by the sol-gel method, where the seed layers deposited by dip coating of a chemical precursor solution obtained by dissolving zinc acetate dihydrate and monoethanolamine in 2-methoxyethanol onto a (100) Si substrate. The film thickness, porosity, texture, and the size of the crystallites were controlled by varying the molar concentration of precursors, the withdrawal speed, and the number of dip-coating cycles. The ZnO nanorods were grown by CBD in aqueous solution consisting of zinc nitrate hexahydrate and HMTA in batch and continuous-flow reactors. Periodic arrays of ZnO nanorods were obtained on the seed layers patterned by electron or ion beam lithography (fig. 1c). To study the electric charge transport in the nanorods, electrical contacts were formed by the deposition of colloidal graphite, by metal evaporation and by the deposition of Pt using the gas injection system in the SEM. The transport properties were correlated with the structural and optical properties investigated by x-ray diffraction and low-temperature photoluminescence spectroscopy.

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