Study of multiple phonon behavior in Li-doped ZnO thin films fabricated using the sol-gel spin-coating technique

Undoped and lithium-doped zinc oxide (ZnO) thin films have been deposited on sapphire substrates (0001) using the sol-gel method. The effect of doping with various percentages of Li at a particular annealing temperature of 600 A degrees C is studied. The samples are characterized using Xray diffraction (XRD), scanning electron microscopy (SEM), micro-photoluminescence (A mu-PL) and Raman and polarized Raman (PR) spectroscopy. The X-ray diffraction and micro-Raman spectroscopy confirm the presence of lithium substitution for zinc. The wurtzite structure of the lattice is retained, and five multiple phonon Raman modes are observed. The values of the depolarization ratios are calculated from polarized Raman data. Photoluminescence shows a strong emission peak in the near UV at 3.276 eV and negligible visible emission. The PL peak positions in the doped samples nearly coincide with each other, suggesting very similar recombination mechanisms in the nanocrystals.