Improved opto-electrical properties of spray deposited ytterbium doped cadmium oxide thin films

Abstract

Transparent conducting metal oxides (TCOs) associate the properties of high optical transparency and electrical conductivity, which makes them suitable for variety of applications such as window layer in liquid crystal and electroluminescent display devices as well as in solar cells. Among different TCO’s, cadmium oxide (CdO) has received tremendous attention as a potential alternative to Sn-doped In2O3 (ITO) due to its high intrinsic dopability coupled with outstanding mobility and high electrical conductivity. In the present study, for first time the doping of ytterbium (Yb) into CdO films prepared using a simple and effective spray pyrolysis technique demonstrated. The structural, morphological and optoelectronic properties of Yb doped CdO thin films as a function of Yb concentration (1–3 at.%) have been studied. X-ray diffraction, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, optical absorption spectroscopy, luminescence measurements and for electrical properties Hall effect set up in van der Pauw configuration have been employed to study the properties of Yb-doped CdO thin films. Yb doped CdO thin films exhibit excellent optical transparency, with an average transmittance over 75% in the visible region. It is found that Yb doping widens the optical band gap from 2.63 to 2.88 eV, via a Moss–Burstein shift and further decreases to 2.77 eV. The maximum reflectivity of 97.24% achieved for 2.5 at.% Yb:CdO film. The better values of resistivity, carrier concentration, mobility and figure of merit have been obtained for 2.5 at.% Yb:CdO, which are 2.6 × 10−4 Ω cm, 13.9 × 1020 cm−3, 17.39 cm2/Vs and 45.87 × 10−3 (Ω)−1 respectively. The obtained results revealed that Yb dopant has a significant influence on the optoelectronic properties of CdO-based TCO compound.