Oxygen diffusion in zinc-oxide thin films prepared by pulsed-laser deposition

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Oxygen isotopic heterostructural zinc-oxide thin films, i.e., Zn16O/Zn18O/Zn16O, were synthesized. Pulsed-laser deposition was used to deposit the films. First, only 18O2 gas was leaked into the deposition chamber, then 16O-enriched ZnO thin film was deposited, and after this 18O-enriched layer was obtained using 18O radicals as a source of isotopes. Finally, the 16O-enriched layer was deposited by turning off the radical source. The resulting thin films were annealed at various diffusion-annealing temperatures. The change in 18O-diffusion profiles due to annealing was evaluated with secondary ion mass spectrometry (SIMS). The diffusion coefficients were slightly higher near the interface between the thin film and the substrate (inner region) than those near the surface (outer region). The dependencies of oxide ion diffusion on temperature for the outer and inner regions areexpressed as $D_{outer} = 3.2 \times 10^1 \left({_{5.5 \times 10^{-1}}^{1.9 \times 10^3}} \right)\exp \left({-\frac{{397 \pm 42(kJ/mol)}}{{RT}}} \right)cm^2/s$ and $D_{inner} = 6.7 \times 10^1 \left({_{4.2 \times 10^{-5}}^{1.0 \times 10^4}} \right)\exp \left({-\frac{{346 \pm 96(kJ/mol)}}{{RT}}} \right)cm^2/s$. The activation energy is concluded to consist of the enthalpy of the oxygen migration and the oxygen vacancy formation, comparing the present data with the reported theoretical results.
2009-05-01