Structural and optical properties of ZnO thin films grown by RF magnetron sputtering on Si substrates

The structural and optical properties of ZnO thin films grown by a RF magnetron sputtering system on Si substrates were characterized by photoluminescence, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. While no change of the emission properties and the orientation relationship along the a-axis was observed in ZnO films grown on Si (100) and (111) substrates under the same growth conditions, the variation of growth rate caused by RF power and argon/oxygen flow ratio is the key factor for the growth of high-quality ZnO film. In optimized growth conditions, ZnO films showed the strong UV emission of the ZnO band-edge, weak deep-level emission, and an additional peak near 425 nm. Also, the shift of the blue-region peak (410 - 425 nm) was closely related with grain size. In-situ thermal treatment led to improvement of ZnO film quality, showing strong UV emission and the elimination of blue emission.