Different defect levels configurations between double layers of nanorods and film in ZnO grown on c-Al2O3 by MOCVD

Epitaxial ZnO structures with inherent two layers of nanorods layer on film layer were fabricated on c-Al2O3 by metal-organic chemical vapor deposition (MOCVD) and studied by photoluminescence. Specially, photoluminescence spectra for the film layer were obtained by rendering the excitation from the substrate side. Different defect levels configurations between nanorods and film were revealed. Zinc vacancies tend to form in top nanorods layer, whereas abundant zinc-oxygen divacancies accumulate in bottom film layer. An acceptor state with activation energy of ~200 meV is exclusive to the film layer. The stacking fault related acceptor and Al introduced donor are present in both layers. Besides, two other defect related donors contained in the nanorods layer perhaps also exist within the film layer.