Atomic Layer Deposition of CoxOy Films: Oxidants versus Composition

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AbstractCobalt oxides (CoxOy) have shown great potential for applications in catalysts, sensors, and energy storage fields, and their performance remarkably depends on their oxidation states. Herein, CoxOy films with precisely controlled composition are first introduced by atomic layer deposition (ALD) using bis(N,N0‐di‐iso‐propylacetamidinato)cobalt(II) (Co(iPr2‐Me‐AMD)2) as Co precursor and H2O/O3 as oxidants. The results show that the ALD processes using both oxidants exhibit typical self‐limiting characteristic, where cubic‐CoO films, with growth rate of 0.045 nm per cycle, are obtained at 150–200 °C using H2O oxidant, while cubic‐Co3O4 films, with growth rate of 0.05 nm per cycle, can be deposited at 200–225 °C using O3 oxidant. Both CoO and Co3O4 films show dense, smooth microstructure, and good crystallinity with typical columnar crystal feature, where the Co3O4 film shows smaller columnar size because the O3 promotes rapid nucleation with relatively higher density of nucleation sites. The thermodynamic growth mechanism of ALD process is established via density functional theory calculations, which demonstrates that the exothermic reaction path of O3 is more energetically than that of H2O. Both films possess relatively low resistivity of ≈10−1 Ω cm−1 with p‐type semiconductor behavior, which shows promising application potentials of these films.