No abstract

In this work, we present a detailed Raman scattering study to clarify the origin of the mode at 379 cm −1 which is observed in Raman spectra of the ZnO films grown on c-sapphire substrates and generally attributed to the A 1 -transverse optical (A 1 -TO) mode of ZnO. The studied ZnO films were deposited by metal-organic chemical vapor deposition on c-sapphire and (0001) ZnO substrates. In the z(−,−)z backscattering configuration, the A 1 -TO mode is forbidden, while the 379 cm −1 peak is still observed in the as-deposited film grown on sapphire substrate. However, this mode is not observed in Raman spectra of the as deposited film grown on ZnO substrate. We suggest that the peak at 379 cm −1 is the E 1g mode of the sapphire substrate which is allowed in z(−,−)z backscattering configuration. The effects of annealing, the substrate and the collection cross-section on Raman active modes were analyzed.