Surface roughness and electrical conductivity of the SnO2ultra-thin layers investigated by X-ray reflectivity

Spray pyrolysis technique was applied to deposit two sets of ultra-thin layers of tin dioxide (SnO2). For the first and second sets, 0.01 and 0.05 molar precursor solutions were prepared, respectively. In both sets, utilizing the X-ray reflectivity (XRR) technique, the effect of precursor concentration (PC) and precursor volume (PV) on the layer structure are investigated. The layer thickness of the samples, in each set, is a PV-dependent parameter. For the same PV, samples with higher PC have a larger thickness and higher density. The electron density profiles deduced from XRR data analyses establish a link between measured values of sheet resistance and electron densities. The samples with higher PV and PC show less sheet resistance. The quantum size effect was utilized to show that the surface roughness for layers of more than almost 200 angstrom of samples in set two plays no role in the layer conductivity. Meanwhile, the same effect explains, adequately, the role of the surface roughness in the resistivity of the ultra-thin layers in Set 1.