Synthesis and characterization of nanocrystalline CdZnO thin films prepared by sol-gel dip-coating process

doi:10.1016/j.tsf.2011.06.075

Thin Solid Films

Volume 520, Issue 4, 1 December 2011, Pages 1228-1232

https://doi.org/10.1016/j.tsf.2011.06.075 Get rights and content

Abstract

Nanocrystalline Cd_xZn_1 − xO thin films with different Cd volume ratios in solution (x = 0, 0.25, 0.50, 0.75 and 1) have been deposited on glass substrate by sol-gel dip-coating method. The as-deposited films were subjected to drying and annealing temperatures of 275 °C and 450 °C in air, respectively. The prepared films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV–vis spectroscopy and dc-electrical measurements. The results show that the samples are polycrystalline and the crystallinity of the films enhanced with x. The average grain size is in the range of 20–53 nm. The atomic percent of Cd:Zn was found to be 9.50:1.04, 6.20:3.77 and 4.42:6.61 for x = 0.75, 0.50 and 0.25, respectively. It was observed that the transmittance and the band gap decreased as x increased. All the films exhibit n-type electrical conductivity. The resistivity (ρ) and mobility (μ) are in the range of 3.3 × 10² − 3.4 × 10^− 3 Ω cm, and 1.5 − 45 cm² V^− 1 s^− 1 respectively. The electron density lies between 1.26 × 10¹⁶ and 0.2 × 10²⁰ cm^− 3.

Introduction

In recent years, the structural, optical and electronic properties of wide band gap metal oxides such as In₂O₃, SnO₂, ZnO, and CdO have attracted significant research interests. Those are very important materials due to their high transparency in the visible region and also for having a very high conductivity. CdO is an n-type semiconductor, with a direct band gap of approximately 2.5 eV [1] which is lower than that of ZnO (~ 3.3 eV [2]); however CdO thin films show low resistivity due to the defects of oxygen vacancies and cadmium interstitials [3]. Thin films of ZnO have been applied in many optoelectronic devices such as laser diodes or short wavelength light emitting diodes because of its large exciton binding energy of 60 meV [4]. Generally, ZnO exhibits luminescence bands in the UV and visible regions [5], [6]. To have luminescence from UV to blue and green light spectra, the optical band gap of ZnO should be tuned. CdO has been considered as a suitable material for band gap engineering [7]. The incorporation of Cd into ZnO is very useful for the fabrication of ZnO/ZnCdO heterojunctions and super lattices, which are key elements in ZnO based light emitters and detectors [8], [9], [10]. Several techniques have been used to prepare CdO–ZnO alloy films like electrodeposition [11], molecular beam epitaxy [12], sol-gel [13] and spray pyrolysis [14]. In the present study, we have reported the compositional, structural, morphological, optical and electrical properties of the Cd_xZn_1 − xO nanocrystalline thin films by different solution volume ratios, deposited by facile and inexpensive sol-gel dip-coating method.

Section snippets

Preparations of films by sol-gel

CdZnO thin films have been deposited on glass substrates using sol-gel dip coating process. Cadmium acetate dihydrate [Cd(COOCH₃)₂⋅2H₂O] and zinc acetate dihydrate [Zn(COOCH₃)₂⋅2H₂O] have been taken as the source cadmium and zinc, respectively. 2-methoxyethanol (C₃H₈O₂) and monoethanolamine (C₂H₇NO, MEA) were used as a solvent and stabilizer, respectively. At first, zinc acetate dihydrate and cadmium acetate dihydrate of 0.5 M were prepared separately. In order to prepare ZnO precursor solution,

Structural, morphological and compositional studies

Fig. 1 shows the XRD patterns of the Cd_xZn_1 − xO thin films. It can be distinguished from Fig. 1 that all samples are polycrystalline. The diffraction peaks in the XRD pattern consist of the diffraction peaks of ZnO and CdO. The observed diffraction peaks (100), (002) and (101) for ZnO and (111), (200) and (220) for CdO are in good agreement with the reported data [16], [17]. It is also illustrating that the Cd_xZn_1 − xO thin films are a binary mixture composed of a NaCl cubic structure (CdO) and a

Conclusion

Cd_xZn_1 − xO thin films were deposited on glass substrates by sol-gel dip-coating method. The variation of the structural, morphological, compositional, optical and electrical properties of the films was investigated as a function of x (Cd volume ratio in solution). The structural investigation revealed that the films are polycrystalline and the phase transition occurs from wurtzite to cubical as x varies from 0 to 1. The grain size of nanostructured CdZnO thin films increases with increasing of

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Synthesis and characterization of nanocrystalline CdZnO thin films prepared by sol-gel dip-coating process

Abstract

Introduction

Section snippets

Preparations of films by sol-gel

Structural, morphological and compositional studies

Conclusion

Solid State Commun.

Electrochem. Commun.

Thin Solid Films

J. Luminescence

Chem. Phys. Lett.

Inorg. Chem. Commun.

J. Crys. Growth

Sol. Energ. Mater. Sol. Cells

J. Comput. Phys.

Chem. Phys. Lett.

Thin Solid Films

Sensors Actuat B

Appl. Surf. Sci.

Sol. Energy

Int. J. Hydrogen Energ.

J. Alloy Compd.

Phys. B

Nat. Mater.