Optical and structural properties of ZnO for transparent electronics

During the last years there is has been an enormous research effort on the materials and processes for the production of transparent electronic devices grown on flexible polymeric substrates as well as on rigid substrates, such as Si and glass. The deposition of Transparent Conductive Oxides (TCOs) characterized by superior optical and electrical properties, in combination to desirable growth characteristics, compatible to polymeric substrates, is of considerable importance. Among all TCO materials, Zinc Oxide (ZnO) has emerged as one of the most promising materials due to its optical and electrical properties, its high chemical and mechanical stability and, due to its abundance, low cost compared with the most currently used TCO materials. In this work, we study the effect of the deposition parameters of ZnO thin films in terms of their optical, structural and nanomechanical properties by employing Spectroscopic Ellipsometry (SE) in the Vis-fUV spectral region, and X-Ray Diffraction techniques. The SE measurements allowed the determination of the optical properties of the ZnO thin films with deposition time and gas partial pressure, whereas the XRD measurements revealed that the ZnO thin films are preferentially grown parallel to (002) axis, in grains less than 10 nm. Furthermore, nanomechanical testing through nanoindentation indicates a thickness controlled fracture mechanism (pop-in events) affecting the durability of the deposited ZnO thin films.