Microkinetic Model for Oxygen Interstitial Injection from the ZnO(0001) Surface into the Bulk

Semiconductor surfaces provide efficient pathways for injecting native point defects into the underlying bulk. The present work constructs a quantitative microkinetic model for the injection of oxygen interstitial atoms from the polar Zn-terminated ZnO(0001) surface into the bulk. Rate constants for defect interaction with the surface and in the bulk were determined by a global optimization procedure of simulations fitted to self-diffusion profiles from isotopic gas-solid exchange experiments. Key activation barriers are 2.0 eV for injection, 0.62 eV for hopping diffusion, and 1.6 eV for lattice exchange. The injection barrier does not differ greatly from that for nonpolar TiO₂(110), but the coverage of injectable oxygen increases with temperature, in contrast to the behavior of TiO₂ and gas adsorption in general.