Phase transformation on zinc selenide thin films deposited by photo-assisted chemical bath method: The effect of annealing temperature

Zinc selenide (ZnSe) thin films have been deposited on glass substrates via photo-assisted chemical bath deposition technique. The films were annealed at different temperatures 100, 150, 200, 250, 300, 350 and 400 degrees C in air for 2 h and were characterized using different techniques. The glancing incidence X-ray diffraction (GIXRD) showed that the as-deposited sample and films annealed from 100 to 200 degrees C contained secondary peaks due to combine effects of ZnSe and unreacted Zn and Se. The films annealed at 250 and 300 degrees C showed pure hexagonal ZnSe phase while those annealed at 350 and 400 degrees C changed to hexagonal ZnO. The estimated crystallite sizes were found to decrease in size with increased annealing temperature. The change in phase was also observed in Raman spectroscopy, scanning electron microscopy and UV-visible spectroscopy. Atomic force micrographs showed decrease in surface roughness with an increase in the annealing temperature. Energy band gap increased with annealing temperature. Three emission bands due to band-edge and defect levels were observed in the photoluminescence spectroscopy. The lifetime decay did not show any ordered dependence on the annealing temperature. The sample annealed at 250 degrees C was considered because its parameters such as the diffraction angle, lattice constants and energy band gap were closest to the bulk ZnSe. The Commision Internationale de L' Eclairage showed blue emission color with color purity between 56 and 97%. The films especially 250 degrees C sample was recommended for lighting applications.