Photoluminescence of thermal-annealed nanocolumnar ZnO thin films grown by electrodeposition

Nanostructured zinc oxide thin films formed by partially oriented hexagonal columns with dimensions of about 100 nm × 300 nm have been prepared by cathodic electrodeposition on conducting glass substrates. After subsequent thermal annealing in air at different temperatures (100-500 °C), structural information on the films was obtained by means of non-resonant Raman spectroscopy. Increasing the annealing temperature leads to a higher degree of crystallinity. The photoluminescence activity of the samples (at low temperature) also improves for increasing annealing temperatures in two ways: increasing the intensity of the near-band edge emission and decreasing the width of the excitonic peak. No emission band in the visible is detected, which attests the high quality of the ZnO nanocolumnar films.