Optical band gap and refractive index dispersion parameters of boron-doped ZnO thin films: A novel derived mathematical model from the experimental transmission spectra

Abstract

We report on optical properties of undoped ZnO and Boron doped ZnO (B-ZnO) thin films prepared by sol-gel dip coating technique. Optical transmittance and reflectance were investigated to get a deeper insight into the optical properties and optoelectronic behavior of B-ZnO thin films. The main aim of this work is to resolve the major challenge facing researchers working on thin films of finding the proper physical model that explains the correlations between the film thickness and the optical band gap. We propose a novel derived mathematical model to interpret the experimental transmittance as a function of wavelength (λ) of amorphous and crystal semiconductors and dielectric thin films. The proposed model reproduces the values of the optical band gap energy of the investigated thin films that are in good agreement with Tauc plot method and other optical models. We found that optical band gap of B-ZnO has decreased from 3.434 eV to 3.256 eV as boron concentration in ZnO films is increased from 0% to 10%. In addition, we found that Urbach energy values have drastically decreased as the concentration of boron introduced into ZnO thin films was increased. We implemented the newly derived model to reproduce optical properties such as the refractive index dispersion and oscillator parameters that were investigated using other different optical models such as Cauchy, Wemple Di-Domenico, Sellemeier, Spitzer-Fan and Drude. Our results indicate that optical parameters of (B-ZnO) thin films are strongly dependent on boron concentration.