Sol-Gel and Hydrothermal Derived Mn-doped ZnO Films with Optical and Piezoelectric Properties

In this work, Mn-doped ZnO films obtained by sol-gel (SG) and hydrothermal (HT) methods were
prepared for possible optical and piezoelectric applications. The amount of Mn dopant was 1, 2 and
5at% and the films were deposited on glass and Si/SiO2/Ti/Pt substrates. The comparative
characterization of the films for their structure, morphology, optical and piezoelectric properties was
achieved. SG films exhibit equiaxed nanoparticles, with diameters around 50 nm, while uniform 1D
nanorods, sized about 30 nm diameter and 200-300 nm length, were obtained for the films prepared
by HT method. XRD diffractograms reveal the presence of zincite phase, with an improvement in
crystallinity of the HT films, which present a stronger orientation along (002) plane (c-axis).
Spectroscopic ellipsometry shows that the films obtained by SG are much thinner than the ones
obtained by HT, and that the refractive index is increasing with the percent of dopant. The maximum
transmission is the highest for the undoped ZnO film and decreases with Mn concentration, but
remains over 78% in the visible range. The piezoelectric tests have shown for both SG and HT
derived films low d33 coefficient. The highest value of d33 is obtained for HT film with 2at% dopant.
Based on the obtained results the research directions for the improvement of piezoelectric properties
could be outlined.