SnO2 is a transparent n-type semiconductor with a wide band gap of 3.6 eV and high conductivity when doped.  It is commonly employed as a transparent conducting layer in thin film solar cells, coating to reflect infrared heat in energy conserving windows, and as thin film detectors in gas sensors.  Requirements in the efficiency of these application are conformity, uniformity, and pin-hole free films; thus atomic layer deposition (ALD) is positioned as the technique of choice. However, wide-spread application has been retarded due to limitations of precursors and lack of mechanistic understanding regarding the deposition processes.   ALD of SnO2 was demonstrated using a tin(II) precursor paired with hydrogen peroxide at low temperatures, useful for coating soft substrates like polymer-based electronics.  Through understanding the oxidation process, we aim to control oxygen deficiencies and conductivity of SnO2 films.  Additionally, presence of a SnO interfacial layer acts as a barrier and inhibits conductance between SnO2 and conductive contact.  Traditional methods for mechanistic investigation are limited in this scope by indirect determination of metal oxidation state and coordination environment, thus direct investigative methods are required.                A novel method to investigate nucleation in ALD; specifically a study of SnO2 as investigated by x-ray absorption techniques, will be discussed.  Reaction of tin(II) precursor on silica, its oxidation by H2O2 to tin(IV) and change in coordination environment during this process was observed by x-ray absorbance spectroscopy.  This data coupled with Raman spectroscopy, x-ray photoelectron spectroscopy, and chemical tests confirm the mechanism and stoichiometric nature of the ALD process.  However, oxidation of the Sn2+ to Sn4+ occurs through reaction of Sn2+ precursor with surface-bound peroxide species rather than oxidation by additional H2O2 of surface Sn2+.  This insight points to using other controlled oxidations for the growth of thin film oxides relevant to electronic materials, catalysis, and energy storage.

X-ray absorption study on nucleation of SnO<sub>2</sub> thin films grown by atomic layer deposition

246th National Meeting (2013)

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X-ray absorption study on nucleation of SnO2 thin films grown by atomic layer deposition

X-ray absorption study on nucleation of SnO₂ thin films grown by atomic layer deposition