Nanostructural Features and Optical Performance of RF Magnetron Sputtered ZnO Thin Films

Zinc oxide (ZnO) thin films were grown on silicon substrate by RF (radio frequency) magnetron sputtering. Surface topography of these films exhibited a nanostructured granular appearance with the size of individual grains between 50 to 100 nm. Corresponding cross-sectional electron micrographs revealed columnar grains in the form of aggregated nanorods/wires with length of about 500 nm, similar to the thickness of these thin films of ZnO nucleated and grown vertically on the silicon substrate. High resolution lattice scale imaging using high resolution transmission electron microscope (HRTEM) elucidated the single crystalline 100 planes of hexagonal-ZnO constituting the columnar grains with the individual nanorod diameter between 3 and 4 nm. The photoluminescence measurements showed the prominent emission peak at around 460 nm for the blue band, normally attributed to intrinsic defects in particular interstitial zinc (Zn). These films were further characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and electron paramagnetic resonance (EPR) to evaluate various aspects on preferred growth orientations, band structures and vibrational modes originated in such fascinating nano-grained thin films of ZnO. The present investigations inferred that these films are advantageous in various potential applications for fabricating nano-scaled devices.