Raman-active Froehlich optical phonon mode in arsenic implanted ZnO

In this letter, using both off-resonant and resonant Raman spectroscopic techniques, the correlation of optical phonons and structural disorder in As+ implanted ZnO single crystals has been investigated. An additional broad peak shoulder at 550 cm-1 between the transverse optical and longitudinal optical (LO) phonons was clarified to be resonant Froehlich optical phonon mode in the framework of effective dielectric function. Under resonance condition, an asymmetric broadening and softening of the LO phonon along with a blueshifted luminescent peak revealed the decreasing phonon coherent length and nanocrystallization with increasing fluence, respectively, in good agreement with the observations of transmission electron microscopy and atomic force microscopy