Raman spectroscopy of (Mn, Co)-codoped ZnO films

Raman spectra of (Mn, Co)-codoped ZnO films were investigated as functions of laser line and temperature. It is shown that the Raman shifts for different phonon modes exhibit redshift with temperature increasing, which can be attributed to the anharmonic effect in the material. Strong resonant Raman spectra of multi-LO phonons were observed as well for the films with the exciting photon energy higher than the direct band gap. Compared with the Raman spectra for ZnO films, the Mn, Co codoping effect on the spectra is revealed by the presence of additional phonon modes at 275 and 642 cm(-1) and another intensive phonon mode at around 524 cm(-1). With postannealing, Raman intensity of these phonon modes decrease, owing to the incorporation of oxygen into the films. Origins of the different phonon modes in the spectra are discussed as well.