The effects of Co/Ce co-doped ZnO thin films: an optical and defect study

Abstract

Abstract Ce-doped ZnCoO (Zn0.99-xCo0.01CexO) thin films (with x = 0.00 to 0.05 in increments of 0.01) were grown using the sol–gel technique to investigate the influence of defects on their optical properties. By applying a Double Facet Coated Substrate (DFCS) theoretical transmittance model to analyze the optical transmittance data, the thickness, absorption loss, extinction coefficient, and refractive index of the thin films were determined. The films’ thicknesses and refractive indices ranged from $$350$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>350</mml:mn> </mml:mrow> </mml:math> to $$455$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>455</mml:mn> </mml:mrow> </mml:math> nm and $$1.71$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>1.71</mml:mn> </mml:mrow> </mml:math> to $$2.02$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>2.02</mml:mn> </mml:mrow> </mml:math> , respectively. The optical band gap fluctuates as the Ce concentration increases from 0.00 to 0.05, and the extinction coefficient fluctuates with Ce concentration, and a maximum occurs at the 4% Ce concentration following the Sellmeier dispersion relation. However, the highest Urbach energy, $$904\pm 613$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>904</mml:mn> <mml:mo>±</mml:mo> <mml:mn>613</mml:mn> </mml:mrow> </mml:math> meV, was observed for the 2% Ce-doped film. The photoluminescence (PL) spectra of Co/Ce co-doped ZnO thin films reveal the relative contributions of defects, namely Zni (zinc interstitials), VZₙ (zinc vacancies), and Oi (oxygen interstitials). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to analyze the structural properties and surface morphology of the films. Additionally, energy-dispersive spectroscopy (EDS) was used to determine the elemental composition of the thin films. This study demonstrates the effective use of the DFCS model to accurately determine the refractive index and extinction coefficient, two critical parameters for modeling photolithographic processes in the semiconductor industry.