Selective SnO_x Atomic Layer Deposition Driven by Oxygen Reactants

SnO_x thin films were successfully deposited by the thermal atomic layer deposition (ALD) method using N,N′-tert-butyl-1,1-dimethylethylenediamine stannylene(II) as a precursor and ozone and water as reactants. The growth of SnO and SnO₂ films could be easily controlled by employing different reactants and utilizing different ozone and water concentrations, respectively. The formation of both SnO and SnO₂ films exhibited typical surface-limiting reaction characteristics, although their growth behaviors differ from one another. The combined studies of density functional theory calculations and experimental analyses showed that the difference in growth behavior of the SnO and SnO₂ films can be attributed to the stability of ozone and water on the SnO₂ and SnO films. SnO and SnO₂ films have different crystal structures and both films were crystallized from the amorphous to polycrystalline states following an increase in the deposition temperature. The absorbance and refractive index of the thin films were investigated using ultraviolet-visible spectroscopy (UV-vis) and spectroscopic ellipsometry (SE), respectively. SnO_x films formed using ozone and water as a reactant showed an optical band gap of 3.60-3.17 eV and 2.24-2.30 eV and refractive indices of ∼2.0 and ∼2.6, respectively, which correspond to values typical of SnO₂ and SnO. The bilayer structure of SnO/SnO₂ was successfully fabricated on indium tin oxide (ITO) glass with nickel as a top electrode at 100 °C. The SnO/SnO₂ bilayer exhibited diode characteristics with a current rectification ratio of 15. Our results present a simple but highly versatile growth method for producing multilayer oxide films with electronic properties that can be finely controlled.