Impact of air exposure on growth rate and electrical properties of SnO 2 thin films by atmospheric pressure spatial atomic layer deposition

SnO 2 thin film is one of the most studied transparent conductive materials that can be deposited using vacuum-free techniques such as atmospheric pressure spatial atomic layer deposition (AP-SALD). This work studies SnO 2 thin films prepared from tin(II) acetylacetonate and water vapor, with a particular focus on the impact of air exposure during the AP-SALD process on the growth rate and electrical properties of the films. In-situ resistance measurements and ex-situ Hall effect characterization demonstrated that longer exposure time of the growing film surface to the open air ( t air ) at 240 °C led to conductivity degradation, while the film thickness decreases. The theoretical calculations show that −OH and O 2 dm (oxygen molecule adsorbed on the five-coordinated Sn atom, also called O 2 dimer) are the two most stable surface structures. The formation of O 2 dm is shown as the most thermodynamically favorable oxygen-related species on SnO 2 (110) surface formed when the film is exposed to the open air, giving rise to both the decrease of film thickness (associated with the desorption of −OH surface groups) and the increase of film resistivity versus t air . The optimized polycrystalline SnO 2 sample demonstrated relatively good electrical performance, including an electrical resistivity of 9.3 × 10 −3 Ω.cm, carrier density of 9.2 × 10 19 cm −3 , and Hall mobility of 7.3 cm 2 V −1 s −1 at a growth temperature as low as 240 °C. Our findings reveal the critical impact of processing in the open air on the electrical conductivity of the obtained SnO 2 films by AP-SALD coating technology.