Academe Research Journals

International Journal of Chemistry and Material Science

Full Length Research Paper

Study of green and UV emissions in polycrystalline ZnO thin films and spectroscopic properties

Taj Muhammad Khan* and Babar Hussain

National Institute of Lasers and Optronics (NILOP), P.O. Nilore-45650, Islamabad, Pakistan.

*Corresponding author. E-mail: tajakashne@gmail.com. Tel: +92-51-9248671-6; Fax: +92-51-2208051.

Accepted 26 November, 2014

Abstract

In this paper optical emissions and spectroscopic properties of the polycrystalline ZnO thin film is described. ZnO thin films are produced in oxygen deficit environment and annealed in two different environments with oxygen as common rich element. In oxygen ambient, green emission is quenched and shows no stability, while ultraviolet emission exhibits good stability and enhanced intensity. The green and orange emissions are no longer observed simultaneously, though the orange emission can be obtained at the expense of green emission quenching. Raman spectroscopy demonstrates that intensities of the E2 (high) and E1 (low) modes are strongly dependent on annealing environment. The ratio of E1 (low) modes for the two samples is strongly correlated with the density of oxygen vacancies. Oxygen environment results in smooth morphology and comparatively low roughness. The value of urbach-energy is lower in oxygen ambient compared to those in air. The optical constants (n, k) are calculated using spectroscopic ellipsometry in the wavelength regime of 300–1100 nm. A comparison of energy bandgap, roughness and grain size determined by different techniques is made. These properties have manifested compatibility and promising structural and optical properties of polycrystalline ZnO thin films annealed in oxygen compared to air and can be useful in the fabrication of shorter-wavelength light-emitting devices.

Key words: Nanostructured zinc oxide (ZnO), urbach energy, raman spectroscopy, photoluminescence, thin film, optical properties.