A Study on Effect of Sol Aging Time on Optical Properties of ZnO Thin Films: Spectroscopic Ellipsometry Method

Abstract

Background: Due to wide band gap and large excitonic binding energy, being inexpensive, abundance in nature and easy synthesis ZnO is a promising candidate in many applications such as solar cells. Experimental: In the current work a series of ZnO thin films were deposited on glass substrates using sol-gel method to investigate the change in optical behavior of the film with sol aging time (asprepared, 8, 16, 24 and 32 hours) and the annealing temperature (300ᵒC and 500ᵒC). The optical properties of thin films were explored using spectroscopic ellipsometry method including the real and imaginary part of refractive index, real and imaginary part of dielectric function and band gap energy of the layers in the 300-900 nanometer wavelength range. Results: It can be deduced from the results that sol aging time and annealing temperature, affect the optical properties of the samples. Using single oscillator energy model of Wemple and Di Domenico parameters such as free charge carrier concentration ratio to effective mass, and plasma frequency, were calculated. Conclusion: The films prepared using 24 h aged solution, had the highest transmittance and the largest band gap energy.