Photoluminescence and multiphonon resonant Raman scattering in low-temperature grown ZnO nanostructures

Abstract

The authors report on the optical properties of nanocrystalline ZnO grown at 200°C by radio-frequency magnetron sputtering. The nanocrystalline nature of the films was confirmed by cross-sectional transmission electron microscopy. In these films, ZnO nanocrystals with an average size of about 3-5 nm were embedded in an amorphous matrix. The photoluminescence spectra from such nanostructured thin films show the near-band-edge emissions around 3.3 eV. A redshift of about 8-11 cm-1 is observed in the case of first-order longitudinal-optical (LO) phonon of ZnO in such nanostructures when compared to the LO phonon peak of bulk ZnO. The ultraviolet resonant Raman excitation at 77 K shows multiphonon LO modes up to eighth order. © 2006 American Institute of Physics.