Characterization of cadmium doped zinc oxide (Cd : ZnO) thin films prepared by spray pyrolysis method

Abstract

Thin films of cadmium doped zinc oxide (Cd : ZnO) with different cadmium concentrations have been prepared by the spray pyrolysis method on different substrates at 400 °C. The physical properties of the films were studied as a function of increasing cadmium dopant concentration (up to 25 wt%). The films were characterized by different methods to understand their structural, optical and electrical properties. Energy dispersive x-ray diffraction spectroscopy analysis showed that the Cd concentration in the solid film is slightly lower than that of the starting solution. The x-ray diffraction analysis revealed that the films are polycrystalline in nature having a hexagonal wurtzite type crystal structure with a preferred grain orientation in the (0 0 2) direction. Due to Cd doping, the degrees of polycrystallinity increased simultaneously and the orientation of the grains in the (0 0 2) axis is found to be deteriorated. Atomic force microscopy measurements reveal that the surface morphology of the films changes continuously with a decrease in the grain size due to Cd doping. Both photoluminescence and optical measurements showed that the band gap decreases from 3.12 to 2.96 eV with increasing Cd concentration. Increasing the Cd concentration also leads to the broadening of the emission peak and degrading the crystalline quality. The films are highly transparent in the visible region and the absorption edge showed a red shift. The sheet resistance of pure ZnO has been determined as 650 Ω sq−1 cm−1 and is decreased for higher concentrations of Cd doping. The characterization studies clearly indicate the incorporation of Cd into ZnO; hence the observed decrease in the optical band gap and electrical resistivity can be directly attributed to the effect of Cd ion incorporation into the ZnO lattice.

Growth of Zn1−x CdxO nanocrystalline thin films by sol-gel method and their characterization for optoelectronic applications

“…This emission, also explained by the first principle study of native point defects in ZnO, may be due to oxygen anti-site defects [23]. Recently, S. Vijayalakhmi et al [20] reported that the near band edge emission peak vanished at 25 % Cd doping, but in the present study NBE peaks with low intensity have been clearly observed.…”

“…Broad low intense shoulder is observed at 650 nm. This hump of low intensity may be due to oxygen vacancy created during the growth of the samples [20]. From Fig.…”

Effect Cd Doping on the Structural and Optical Properties of ZnO Thin Films

“…Variations in crystallite size with doping concentration may be explained in a number of ways: First, the decrease in crystallite size could be due to an increase in number of Cd atoms, which would exert drag forces on boundary motion and grain growth. Second, the increase in the number of dopant atoms may lead to increased numbers of point defects, which would give rise to higher grain boundary mobility and grain growth rates [1,34].…”

“…The spray pyrolysis method is used for preparing large numbers of pure and doped thin films because the method is simple, inexpensive, and easy to apply for growing uniform films and allows the coating of large areas [1,24]. This work aims to study the effects of doping concentration and annealing on the structural, morphological, and optical properties of Cd-doped ZnO thin films.…”

Effect of cadmium incorporation on the properties of zinc oxide thin films

“…The ZnO (hexagonal) and CdO (cubic) have very different crystal structure, and also, low thermodynamic solubility (~ 2 mol.%) of CdO in CdO-ZnO system make it very difficult to grow single-phase hexagonal Cd x Zn 1−x O thin films with high Cd concentration (Ishihara et al 2006). Different methods can be employed to grow mixed Cd x Zn 1−x O thin films, such as molecular beam epitaxy (Wang et al 2006), sputtering (Ma et al 2011), pulsed laser deposition (Makino et al 2013) and spray pyrolysis (Vijayalakshmi et al 2008). Compared to different methods, the spray pyrolysis method is simplest industrially applicable method to produce metal oxide thin films.…”