Ponente
Descripción
Among semiconductor metallic oxides, zinc oxide (ZnO) is one of the most studied from the scientific community last years, due to its unique chemical and physical properties. Its direct wide band gap (3.37 eV), high exciton binding energy (60 meV), elevated efficiency of radiative recombination and high thermal and mechanical stability at room temperature, make this material an attractive candidate for applications in electronic and optoelectronic devices, such as photodetectors, solar cells and resistive gas sensors. Simple and low-cost deposition techniques, easily scalable to mass production, should be used.
A homemade ultrasonic spray pyrolysis (USP) set-up was developed and nanostructured ZnO thin films were deposited on glass substrates. All deposition parameters were fixed, but the deposition time, thus obtaining films with different thicknesses. Measurements were directed to follow the growth process through time. Films were studied by X-ray Diffraction (XRD), UV–Vis spectroscopy, profilometry and scanning electron microscopy (SEM). Band gap and Urbach energies as well as microstructural parameters were calculated.
The films are polycrystalline with preferential growth in the direction normal to (101) planes and exhibit a single phase hexagonal wurtzite microstructure. Surface reactions of the gas-solid type seems to dominate the deposition. Initially, the films exhibit granular (nanostructured) growth. As thickness increases, granular growth ceases and the formation of grain aggregates begins, thus transforming the film surface from specular to opaque. Therefore, film morphology and optical properties depend on thickness, whereas the microstructural parameters do not show appreciable variations.
