In-related complex defects and emission of in-doped ZnO nanocrystal films

ZnO nanocrystal (NC) films grown by ultrasonic spray pyrolysis, doped with the In atoms in different concentrations and annealed at 400 °C for 4 h in nitrogen flow have been studied. The scanning electron microscopy (SEM), X ray diffraction (XRD), photoluminescence (PL) and X-ray photo electronic spectroscopy (XPS) have been used. It was shown that the PL intensity of near band edge (NBE) emission enlarges significantly and the PL intensity of green PL band suppresses at small In contents ≤ 2.0 at%. The later confirms the occupation of zinc vacancies by In ions with the formation of the substitutional In_Zn donor defects and ZnO crystal quality improving. At higher In contents the new NBE emission band B (3.034eV) appears in PL spectra and its peak shifts to lower energy with In content increasing. The joint analysis of PL and XRD results permits to suppose that the defects responsible for the PL band B are some complexes, which were formed by the coagulation of the substitutional and interstitial In atoms. Simultaneously, the PL intensity and ZnO film crystallinity falling down and the ZnO crystal lattice parameters increase. To study a nature of the In related complex defects, XPS spectra have been investigated for the films with the different In contents. XPS spectrum varying versus In contents has confirmed the complex In defect nature. The dependence of In_i complex defect formation versus In contents in ZnO NC films is analyzed and discussed. The optimal In concentration range to fabricate the ZnO films with high optical parameters has been estimated.