Mechanism of creation and destruction of oxygen interstitial atoms by nonpolar zinc oxide(101̄0) surfaces

Oxygen vacancies (V_O) influence many properties of ZnO in semiconductor devices, yet synthesis methods leave behind variable and unpredictable V_Oconcentrations. Oxygen interstitials (O_i) move far more rapidly, so post-synthesis introduction of O_ito control the V_Oconcentration would be desirable. Free surfaces offer such an introduction mechanism if they are free of poisoning foreign adsorbates. Here, isotopic exchange experiments between nonpolar ZnO(101̄0) and O₂gas, together with mesoscale modeling and first-principles calculations, point to an activation barrier for injection only 0.1-0.2 eV higher than for bulk site hopping. The modest barrier for hopping in turn enables diffusion lengths of tens to hundreds of nanometers only slightly above room temperature, which should facilitate defect engineering under very modest conditions. In addition, low hopping barriers coupled with statistical considerations lead to important qualitative manifestations in diffusionviaan interstitialcy mechanism that does not occur for vacancies.