Correlation of ZnO thin film surface properties with conductivity

Technological demands for the fabrication of nanostructured active coatings provide renewed motivation for understanding the properties that control the morphology of the thin film surface. With decreasing structure size, the issues of finite size and shape effects become non-negligible including issues of stability against decay and structural rearrangement. The surface of the wide band gap semiconductor ZnO is known to be very active, with a wide variety of absorption and chemisorptions phenomena taking place. These processes can alter the charge carrier distribution in the sub-surface region and locally change the doping levels. There is a limited amount of literature dedicated to systematic and detailed studies on the surface evolution with growth parameters and their effect on the ZnO surface conductivity under reduction/oxidation. Therefore, this work focuses on the analysis of the thin ZnO film surface properties by studying specific surface parameters such as amplitude related parameters (average roughness, the root mean square), mixed parameters (surface area ratio), functional parameters for characterizing bearing and fluid retention (skewness), and spatial parameters (the fractal dimensions) as they correlate with the film conductivity changes under subsequent exposure to UV light (as reductor factor) and ozone (as surface oxidant agent). All ZnO thin films of different thicknesses were grown by the dc planar magnetron sputtering technique under the same sputtering conditions.