Enhanced violet photoemission of nanocrystalline fluorine doped zinc oxide (FZO) thin films

Abstract

Highly stable fluorine doped nanocrystalline zinc oxide thin films were prepared on corning glass substrates by aerosol assisted chemical vapor deposition (AACVD) at variable deposition temperature of 360°C, 380°C and 420°C. Especially, the optimum deposition temperature was investigated for high intense violet emission. The film crystallinity improved with the increasing deposition temperature and highly textured film was obtained at 420°C. The films exhibited surface morphology variation from spherical to platelets due to deposition temperature effect, analyzed by field emission scanning electron microscope (FE-SEM). Higher growth rate observed at 420°C which leads larger grains and lowest resistivity of ∼5.77Ωcm among the deposited films which may be due to reduction in zinc vacancies and grain boundary area. Zinc vacancies are acts as electron killer centres. UV–visible spectra indicated higher transmittance (83–90%) in the visible region. Red shift of optical absorption edges associated with the increase in particle size consistent well with the XRD results. Reduced E2(high) intensity was observed in Raman spectra, for the film deposited at 380°C which indicates decreased oxygen incorporation confirmed by PL spectra. Especially, enhanced violet emission observed at 3.06eV for the films deposited at 380°C due to electronic transition from the defect level of zinc vacancies to the conduction band, probably attributed to enhanced incorporation of ‘F’ into ‘O’ sites associated with increased Zn vacancies and also decreased oxygen incorporation consistent with the electrical and Raman analyses.