Tunable Semiconducting Behavior and Linear-Nonlinear Optical Properties of Ag-Sn Dual-Doped Nanocrystalline CdO Thin Films for Optoelectronics

Abstract

Semiconductor-based thin films have a great impact on determining the anticipated optoelectronic device construction and the advancement of cutting-edge applications. Herein, Ag and Sn dual-doped nanocrystalline transparent conducting CdO thin films were prepared on glass substrates using a cost-effective spray coating method, and their structural, morphological, optical, and semiconducting behaviors were investigated. The successful incorporation of Ag and Sn resulted in the polycrystalline nature of the deposited films without the additional peaks, as verified by X-ray diffraction (XRD) analysis. The XRD report also revealed the enhanced crystallinity (65%) at the higher doping level (3 wt % Ag and Sn-doped CdO film). All the deposited CdO films exhibited homogeneous, spherical, or round-shaped grains, with agglomeration revealed by scanning electron microscopy analysis. UV-visible spectroscopy was utilized to determine the linear and nonlinear optical properties of the deposited CdO thin films, and a reduction in the band gap from 3.891 to 3.772 eV was observed. A significant enhancement in the first- and third-order nonlinear susceptibility and nonlinear refractive index of the doped CdO films was also observed with increasing doping concentration. Hall effect data were collected at room temperature to investigate the electrical properties of all of the CdO films. The charge carrier concentration of CdO thin films was increased from 142.08 × 10¹⁸ to 169.10 × 10¹⁸ cm^-3, and the highest conductivity was found to be 192 s/cm on doping 3 wt % Ag-Sn. All the CdO thin films exhibited n-type conductivity, while an incredible n-type to p-type charge carrier transition was noticed at a higher doping level (3 wt % Ag-Sn). The findings of the current work are expected to advance the synthesis of semiconductor thin films through cost-effective spray coating methods for optoelectronic device applications.

1

(a) Schematic diagram of the experimental setup for the deposition of CdO thin films and (b) photographs of the deposited pure CdO, CAS-1, CAS-2, and CAS-3 thin films.

2

X-ray diffraction (XRD) patterns of CdO and CAS films.

3

Variation of the (a) dislocation density and lattice strain, and (b) crystallinity and crystal size of the deposited pure and Ag–Sn dual-doped CdO thin films as a function of doping concentrations.

4

Scanning electron microscopy images of the (a) pure CdO, (b) CAS-1, (c) CAS-2, and (d) CAS-3 films.

5

Histogram images with average particle size of the (a) pure CdO, (b) CAS-1, (c) CAS-2, and (d) CAS-3 films.

6

Energy dispersive spectrum of the pure CdO and CAS thin films.

7

Variation of (a) optical transmittance, (b) extinction coefficient, (c) reflectance, (d) optical band gap with photon energy, and (e) refractive index of pure and Ag–Sn dual-doped CdO thin films.

8

Variation of (a) optical dielectric constant, ε₁, (b) first-order nonlinear susceptibility, χ⁽¹⁾, (c) third-order nonlinear susceptibility, χ⁽³⁾, and (d) nonlinear refractive index, n ₂ of pure and Ag–Sn dual-doped CdO thin films.

9

Variations of (a) conductivity and resistivity, and (b) Hall mobility (μ_H) and carrier concentrations (n) of pure and Ag–Sn dual-doped CdO thin films.